C backend: support coroutines

classlib/src/main/java/org/teavm/classlib/java/lang/TObject.java

@@ -15,21 +15,24 @@
  */
 package org.teavm.classlib.java.lang;
 
+import org.teavm.classlib.PlatformDetector;
 import org.teavm.dependency.PluggableDependency;
 import org.teavm.interop.Address;
 import org.teavm.interop.Async;
+import org.teavm.interop.AsyncCallback;
 import org.teavm.interop.DelegateTo;
 import org.teavm.interop.Rename;
 import org.teavm.interop.Structure;
 import org.teavm.interop.Superclass;
 import org.teavm.interop.Sync;
+import org.teavm.interop.Unmanaged;
 import org.teavm.jso.browser.TimerHandler;
 import org.teavm.platform.Platform;
 import org.teavm.platform.PlatformObject;
 import org.teavm.platform.PlatformQueue;
 import org.teavm.platform.PlatformRunnable;
-import org.teavm.platform.async.AsyncCallback;
 import org.teavm.runtime.Allocator;
+import org.teavm.runtime.EventQueue;
 import org.teavm.runtime.RuntimeArray;
 import org.teavm.runtime.RuntimeClass;
 import org.teavm.runtime.RuntimeObject;
@@ -39,25 +42,26 @@ public class TObject {
     Monitor monitor;
 
     static class Monitor {
+        static final int MASK = 0x80000000;
+
         PlatformQueue<PlatformRunnable> enteringThreads;
         PlatformQueue<NotifyListener> notifyListeners;
         TThread owner;
         int count;
+        int id;
 
-        public Monitor() {
+        Monitor() {
             this.owner = TThread.currentThread();
-            enteringThreads = Platform.createQueue();
-            notifyListeners = Platform.createQueue();
         }
     }
 
-    interface NotifyListener extends PlatformRunnable {
+    interface NotifyListener extends PlatformRunnable, EventQueue.Event {
         boolean expired();
     }
 
     static void monitorEnterSync(TObject o) {
         if (o.monitor == null) {
-            o.monitor = new Monitor();
+            createMonitor(o);
         }
         if (o.monitor.owner == null) {
             o.monitor.owner = TThread.currentThread();
@@ -83,7 +87,7 @@ public class TObject {
 
     static void monitorEnter(TObject o, int count) {
         if (o.monitor == null) {
-            o.monitor = new Monitor();
+           createMonitor(o);
         }
         if (o.monitor.owner == null) {
             o.monitor.owner = TThread.currentThread();
@@ -95,13 +99,23 @@ public class TObject {
         }
     }
 
+    private static void createMonitor(TObject o) {
+        if (PlatformDetector.isLowLevel()) {
+            int hashCode = hashCodeLowLevel(o);
+            o.monitor = new Monitor();
+            o.monitor.id = hashCode;
+        } else {
+            o.monitor = new Monitor();
+        }
+    }
+
     @Async
     static native void monitorEnterWait(TObject o, int count);
 
-    static void monitorEnterWait(final TObject o, final int count, final AsyncCallback<Void> callback) {
+    static void monitorEnterWait(TObject o, int count, AsyncCallback<Void> callback) {
-        final TThread thread = TThread.currentThread();
+        TThread thread = TThread.currentThread();
         if (o.monitor == null) {
-            o.monitor = new Monitor();
+            createMonitor(o);
             TThread.setCurrentThread(thread);
             o.monitor.count += count;
             callback.complete(null);
@@ -113,7 +127,12 @@ public class TObject {
             callback.complete(null);
             return;
         }
-        o.monitor.enteringThreads.add(() -> {
+
+        Monitor monitor = o.monitor;
+        if (monitor.enteringThreads == null) {
+            monitor.enteringThreads = Platform.createQueue();
+        }
+        monitor.enteringThreads.add(() -> {
             TThread.setCurrentThread(thread);
             o.monitor.owner = thread;
             o.monitor.count += count;
@@ -122,47 +141,73 @@ public class TObject {
     }
 
     @Sync
-    static void monitorExit(final TObject o) {
+    static void monitorExit(TObject o) {
         monitorExit(o, 1);
     }
 
     @Sync
-    static void monitorExit(final TObject o, int count) {
+    static void monitorExit(TObject o, int count) {
         if (o.isEmptyMonitor() || o.monitor.owner != TThread.currentThread()) {
             throw new TIllegalMonitorStateException();
         }
-        o.monitor.count -= count;
+
-        if (o.monitor.count > 0) {
+        Monitor monitor = o.monitor;
+        monitor.count -= count;
+        if (monitor.count > 0) {
             return;
         }
 
-        o.monitor.owner = null;
+        monitor.owner = null;
-        if (!o.monitor.enteringThreads.isEmpty()) {
+        if (monitor.enteringThreads != null && !monitor.enteringThreads.isEmpty()) {
-            Platform.postpone(() -> {
+            if (PlatformDetector.isLowLevel()) {
-                if (o.isEmptyMonitor() || o.monitor.owner != null) {
+                EventQueue.offer(() -> waitForOtherThreads(o));
-                    return;
+            } else {
-                }
+                Platform.postpone(() -> waitForOtherThreads(o));
-                if (!o.monitor.enteringThreads.isEmpty()) {
+            }
-                    o.monitor.enteringThreads.remove().run();
-                }
-            });
         } else {
             o.isEmptyMonitor();
         }
     }
 
+    private static void waitForOtherThreads(TObject o) {
+        if (o.isEmptyMonitor() || o.monitor.owner != null) {
+            return;
+        }
+        Monitor monitor = o.monitor;
+        if (monitor.enteringThreads != null && !monitor.enteringThreads.isEmpty()) {
+            PlatformQueue<PlatformRunnable> enteringThreads = monitor.enteringThreads;
+            PlatformRunnable r = enteringThreads.remove();
+            if (enteringThreads == null) {
+                monitor.enteringThreads = null;
+            }
+            r.run();
+        }
+    }
+
     boolean isEmptyMonitor() {
+        Monitor monitor = this.monitor;
         if (monitor == null) {
             return true;
         }
-        if (monitor.owner == null && monitor.enteringThreads.isEmpty() && monitor.notifyListeners.isEmpty()) {
+        if (monitor.owner == null
-            monitor = null;
+                && (monitor.enteringThreads == null || monitor.enteringThreads.isEmpty())
+                && (monitor.notifyListeners == null || monitor.notifyListeners.isEmpty())) {
+            deleteMonitor();
             return true;
         } else {
             return false;
         }
     }
 
+    private void deleteMonitor() {
+        if (PlatformDetector.isLowLevel()) {
+            int id = monitor.id;
+            setHashCodeLowLevel(this, id);
+        } else {
+            monitor = null;
+        }
+    }
+
     static boolean holdsLock(TObject o) {
         return o.monitor != null && o.monitor.owner == TThread.currentThread();
     }
@@ -200,8 +245,25 @@ public class TObject {
         return getClass().getName() + "@" + TInteger.toHexString(identity());
     }
 
-    @DelegateTo("identityLowLevel")
     int identity() {
+        if (PlatformDetector.isLowLevel()) {
+            Monitor monitor = this.monitor;
+            if (monitor == null) {
+                int hashCode = hashCodeLowLevel(this);
+                if (hashCode == 0) {
+                    hashCode = identityLowLevel();
+                    setHashCodeLowLevel(this, hashCode);
+                }
+                return hashCode;
+            } else {
+                int hashCode = monitor.id;
+                if (hashCode == 0) {
+                    hashCode = identityLowLevel();
+                    monitor.id = hashCode;
+                }
+                return hashCode;
+            }
+        }
         PlatformObject platformThis = Platform.getPlatformObject(this);
         if (platformThis.getId() == 0) {
             platformThis.setId(Platform.nextObjectId());
@@ -209,19 +271,48 @@ public class TObject {
         return Platform.getPlatformObject(this).getId();
     }
 
-    @SuppressWarnings("unused")
+    @DelegateTo("hashCodeLowLevelImpl")
-    private static int identityLowLevel(RuntimeObject object) {
+    private static native int hashCodeLowLevel(TObject obj);
-        int result = object.hashCode;
+
+    @Unmanaged
+    private static int hashCodeLowLevelImpl(RuntimeObject obj) {
+        return obj.hashCode;
+    }
+
+    @DelegateTo("setHashCodeLowLevelImpl")
+    private static native void setHashCodeLowLevel(TObject obj, int value);
+
+    @Unmanaged
+    private static void setHashCodeLowLevelImpl(RuntimeObject obj, int value) {
+        obj.hashCode = value;
+    }
+
+    @Unmanaged
+    private static int identityLowLevel() {
+        int result = RuntimeObject.nextId++;
         if (result == 0) {
             result = RuntimeObject.nextId++;
-            if (result == 0) {
+            if (result == Monitor.MASK) {
-                result = RuntimeObject.nextId++;
+                result = 1;
             }
-            object.hashCode = result;
         }
         return result;
     }
 
+    @DelegateTo("identityOrMonitorLowLevel")
+    private native int identityOrMonitor();
+
+    private static int identityOrMonitorLowLevel(RuntimeObject object) {
+        return object.hashCode;
+    }
+
+    @DelegateTo("setIdentityLowLevel")
+    native void setIdentity(int id);
+
+    private static void setIdentityLowLevel(RuntimeObject object, int id) {
+        object.hashCode = id;
+    }
+
     @Override
     @DelegateTo("cloneLowLevel")
     @PluggableDependency(ObjectDependencyPlugin.class)
@@ -264,13 +355,23 @@ public class TObject {
             throw new TIllegalMonitorStateException();
         }
         PlatformQueue<NotifyListener> listeners = monitor.notifyListeners;
+        if (listeners == null) {
+            return;
+        }
         while (!listeners.isEmpty()) {
             NotifyListener listener = listeners.remove();
             if (!listener.expired()) {
-                Platform.postpone(listener);
+                if (PlatformDetector.isLowLevel()) {
+                    EventQueue.offer(listener);
+                } else {
+                    Platform.postpone(listener);
+                }
                 break;
             }
         }
+        if (listeners.isEmpty()) {
+            monitor.notifyListeners = null;
+        }
     }
 
     @Sync
@@ -280,12 +381,20 @@ public class TObject {
             throw new TIllegalMonitorStateException();
         }
         PlatformQueue<NotifyListener> listeners = monitor.notifyListeners;
+        if (listeners == null) {
+            return;
+        }
         while (!listeners.isEmpty()) {
             NotifyListener listener = listeners.remove();
             if (!listener.expired()) {
-                Platform.postpone(listener);
+                if (PlatformDetector.isLowLevel()) {
+                    EventQueue.offer(listener);
+                } else {
+                    Platform.postpone(listener);
+                }
             }
         }
+        monitor.notifyListeners = null;
     }
 
     @Rename("wait")
@@ -309,17 +418,23 @@ public class TObject {
     private native void waitImpl(long timeout, int nanos) throws TInterruptedException;
 
     public final void waitImpl(long timeout, int nanos, AsyncCallback<Void> callback) {
+        Monitor monitor = this.monitor;
         final NotifyListenerImpl listener = new NotifyListenerImpl(this, callback, monitor.count);
+        if (monitor.notifyListeners == null) {
+            monitor.notifyListeners = Platform.createQueue();
+        }
         monitor.notifyListeners.add(listener);
         TThread.currentThread().interruptHandler = listener;
         if (timeout > 0 || nanos > 0) {
-            listener.timerId = Platform.schedule(listener, timeout >= Integer.MAX_VALUE ? Integer.MAX_VALUE
+            int timeoutToSchedule = timeout >= Integer.MAX_VALUE ? Integer.MAX_VALUE : (int) timeout;
-                    : (int) timeout);
+            listener.timerId = PlatformDetector.isLowLevel()
+                    ? EventQueue.offer(listener, timeoutToSchedule + System.currentTimeMillis())
+                    : Platform.schedule(listener, timeoutToSchedule);
         }
         monitorExit(this, monitor.count);
     }
 
-    private static class NotifyListenerImpl implements NotifyListener, TimerHandler, PlatformRunnable,
+    static class NotifyListenerImpl implements NotifyListener, TimerHandler, PlatformRunnable,
             TThreadInterruptHandler {
         final TObject obj;
         final AsyncCallback<Void> callback;
@@ -329,7 +444,7 @@ public class TObject {
         boolean performed;
         int lockCount;
 
-        public NotifyListenerImpl(TObject obj, AsyncCallback<Void> callback, int lockCount) {
+        NotifyListenerImpl(TObject obj, AsyncCallback<Void> callback, int lockCount) {
             this.obj = obj;
             this.callback = callback;
             this.lockCount = lockCount;
@@ -344,11 +459,19 @@ public class TObject {
 
         @Override
         public void onTimer() {
-            Platform.postpone(() -> {
+            if (PlatformDetector.isLowLevel()) {
-                if (!expired()) {
+                EventQueue.offer(() -> {
-                    run();
+                    if (!expired()) {
-                }
+                        run();
-            });
+                    }
+                });
+            } else {
+                Platform.postpone(() -> {
+                    if (!expired()) {
+                        run();
+                    }
+                });
+            }
         }
 
         @Override
@@ -358,7 +481,11 @@ public class TObject {
             }
             performed = true;
             if (timerId >= 0) {
-                Platform.killSchedule(timerId);
+                if (PlatformDetector.isLowLevel()) {
+                    EventQueue.kill(timerId);
+                } else {
+                    Platform.killSchedule(timerId);
+                }
                 timerId = -1;
             }
             TThread.setCurrentThread(currentThread);
@@ -372,10 +499,18 @@ public class TObject {
             }
             performed = true;
             if (timerId >= 0) {
-                Platform.killSchedule(timerId);
+                if (PlatformDetector.isLowLevel()) {
+                    EventQueue.kill(timerId);
+                } else {
+                    Platform.killSchedule(timerId);
+                }
                 timerId = -1;
             }
-            Platform.postpone(() -> callback.error(new TInterruptedException()));
+            if (PlatformDetector.isLowLevel()) {
+                EventQueue.offer(() -> callback.error(new TInterruptedException()));
+            } else {
+                Platform.postpone(() -> callback.error(new TInterruptedException()));
+            }
         }
     }
 

classlib/src/main/java/org/teavm/classlib/java/lang/TThread.java

@@ -15,10 +15,13 @@
  */
 package org.teavm.classlib.java.lang;
 
+import org.teavm.classlib.PlatformDetector;
 import org.teavm.interop.Async;
+import org.teavm.interop.AsyncCallback;
 import org.teavm.platform.Platform;
 import org.teavm.platform.PlatformRunnable;
-import org.teavm.platform.async.AsyncCallback;
+import org.teavm.runtime.EventQueue;
+import org.teavm.runtime.Fiber;
 
 public class TThread extends TObject implements TRunnable {
     private static TThread mainThread = new TThread("main");
@@ -56,20 +59,26 @@ public class TThread extends TObject implements TRunnable {
     }
 
     public void start() {
-        Platform.startThread(() -> {
+        if (PlatformDetector.isLowLevel()) {
-            try {
+            EventQueue.offer(() -> Fiber.start(this::runThread));
-                activeCount++;
+        } else {
-                setCurrentThread(TThread.this);
+            Platform.startThread(this::runThread);
-                TThread.this.run();
+        }
-            } finally {
+    }
-                synchronized (finishedLock) {
+
-                    finishedLock.notifyAll();
+    private void runThread() {
-                }
+        try {
-                alive = false;
+            activeCount++;
-                activeCount--;
+            setCurrentThread(TThread.this);
-                setCurrentThread(mainThread);
+            TThread.this.run();
+        } finally {
+            synchronized (finishedLock) {
+                finishedLock.notifyAll();
             }
-        });
+            alive = false;
+            activeCount--;
+            setCurrentThread(mainThread);
+        }
     }
 
     static void setCurrentThread(TThread thread) {
@@ -130,10 +139,17 @@ public class TThread extends TObject implements TRunnable {
     static native void switchContext(TThread thread);
 
     private static void switchContext(final TThread thread, final AsyncCallback<Void> callback) {
-        Platform.postpone(() -> {
+        if (PlatformDetector.isLowLevel()) {
-            setCurrentThread(thread);
+            EventQueue.offer(() -> {
-            callback.complete(null);
+                setCurrentThread(thread);
-        });
+                callback.complete(null);
+            });
+        } else {
+            Platform.postpone(() -> {
+                setCurrentThread(thread);
+                callback.complete(null);
+            });
+        }
     }
 
     public void interrupt() {
@@ -176,19 +192,24 @@ public class TThread extends TObject implements TRunnable {
 
     private static void sleep(long millis, final AsyncCallback<Void> callback) {
         final TThread current = currentThread();
-        int intMillis = millis < Integer.MAX_VALUE ? (int) millis : Integer.MAX_VALUE;
         SleepHandler handler = new SleepHandler(current, callback);
-        handler.scheduleId = Platform.schedule(handler, intMillis);
+        if (PlatformDetector.isLowLevel()) {
-        current.interruptHandler = handler;
+            handler.scheduleId = EventQueue.offer(handler, System.currentTimeMillis() + millis);
+            current.interruptHandler = handler;
+        } else {
+            int intMillis = millis < Integer.MAX_VALUE ? (int) millis : Integer.MAX_VALUE;
+            handler.scheduleId = Platform.schedule(handler, intMillis);
+            current.interruptHandler = handler;
+        }
     }
 
-    private static class SleepHandler implements PlatformRunnable, TThreadInterruptHandler {
+    static class SleepHandler implements PlatformRunnable, EventQueue.Event, TThreadInterruptHandler {
         private TThread thread;
         private AsyncCallback<Void> callback;
         private boolean isInterrupted;
         int scheduleId;
 
-        public SleepHandler(TThread thread, AsyncCallback<Void> callback) {
+        SleepHandler(TThread thread, AsyncCallback<Void> callback) {
             this.thread = thread;
             this.callback = callback;
         }
@@ -197,8 +218,13 @@ public class TThread extends TObject implements TRunnable {
         public void interrupted() {
             thread.interruptedFlag = false;
             isInterrupted = true;
-            Platform.killSchedule(scheduleId);
+            if (PlatformDetector.isLowLevel()) {
-            Platform.postpone(() -> callback.error(new TInterruptedException()));
+                EventQueue.kill(scheduleId);
+                EventQueue.offer(() -> callback.error(new TInterruptedException()));
+            } else {
+                Platform.killSchedule(scheduleId);
+                Platform.postpone(() -> callback.error(new TInterruptedException()));
+            }
         }
 
         @Override

classlib/src/main/java/org/teavm/classlib/java/net/impl/TXHRURLConnection.java

@@ -27,10 +27,10 @@ import java.util.Map;
 import org.teavm.classlib.java.net.THttpURLConnection;
 import org.teavm.classlib.java.net.TURL;
 import org.teavm.interop.Async;
+import org.teavm.interop.AsyncCallback;
 import org.teavm.jso.ajax.XMLHttpRequest;
 import org.teavm.jso.typedarrays.ArrayBuffer;
 import org.teavm.jso.typedarrays.Int8Array;
-import org.teavm.platform.async.AsyncCallback;
 
 public class TXHRURLConnection extends THttpURLConnection {
     private XMLHttpRequest xhr;

classlib/src/main/java/org/teavm/classlib/java/util/concurrent/TArrayBlockingQueue.java

@@ -20,6 +20,7 @@ import java.util.Arrays;
 import java.util.Collection;
 import java.util.NoSuchElementException;
 import java.util.Objects;
+import org.teavm.classlib.PlatformDetector;
 import org.teavm.classlib.java.lang.TInterruptedException;
 import org.teavm.classlib.java.lang.TThread;
 import org.teavm.classlib.java.lang.TThreadInterruptHandler;
@@ -27,11 +28,12 @@ import org.teavm.classlib.java.util.TAbstractQueue;
 import org.teavm.classlib.java.util.TCollection;
 import org.teavm.classlib.java.util.TIterator;
 import org.teavm.interop.Async;
+import org.teavm.interop.AsyncCallback;
 import org.teavm.interop.Sync;
 import org.teavm.platform.Platform;
 import org.teavm.platform.PlatformQueue;
 import org.teavm.platform.PlatformRunnable;
-import org.teavm.platform.async.AsyncCallback;
+import org.teavm.runtime.EventQueue;
 
 public class TArrayBlockingQueue<E> extends TAbstractQueue<E> implements TBlockingQueue<E> {
     private Object[] array;
@@ -418,7 +420,11 @@ public class TArrayBlockingQueue<E> extends TAbstractQueue<E> implements TBlocki
         if (waitHandlers != null) {
             while (!waitHandlers.isEmpty()) {
                 WaitHandler handler = waitHandlers.remove();
-                Platform.postpone(() -> handler.changed());
+                if (PlatformDetector.isLowLevel()) {
+                    EventQueue.offer(handler::changed);
+                } else {
+                    Platform.postpone(handler::changed);
+                }
             }
             waitHandlers = null;
         }
@@ -436,7 +442,9 @@ public class TArrayBlockingQueue<E> extends TAbstractQueue<E> implements TBlocki
         waitHandlers.add(handler);
         if (timeLimit > 0) {
             int timeout = Math.max(0, (int) (timeLimit - System.currentTimeMillis()));
-            handler.timerId = Platform.schedule(handler, timeout);
+            handler.timerId = PlatformDetector.isLowLevel()
+                    ? EventQueue.offer(handler, timeLimit)
+                    : Platform.schedule(handler, timeout);
         } else {
             handler.timerId = -1;
         }
@@ -444,7 +452,7 @@ public class TArrayBlockingQueue<E> extends TAbstractQueue<E> implements TBlocki
         TThread.currentThread().interruptHandler = handler;
     }
 
-    class WaitHandler implements PlatformRunnable, TThreadInterruptHandler {
+    class WaitHandler implements PlatformRunnable, TThreadInterruptHandler, EventQueue.Event {
         AsyncCallback<Boolean> callback;
         boolean complete;
         int timerId;
@@ -475,7 +483,11 @@ public class TArrayBlockingQueue<E> extends TAbstractQueue<E> implements TBlocki
             }
             complete = true;
             if (timerId >= 0) {
-                Platform.killSchedule(timerId);
+                if (PlatformDetector.isLowLevel()) {
+                    EventQueue.kill(timerId);
+                } else {
+                    Platform.killSchedule(timerId);
+                }
                 timerId = -1;
             }
             TThread.currentThread().interruptHandler = null;

core/src/main/java/org/teavm/backend/c/CTarget.java

@@ -33,6 +33,7 @@ import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Set;
 import java.util.stream.Collectors;
+import org.teavm.ast.InvocationExpr;
 import org.teavm.ast.decompilation.Decompiler;
 import org.teavm.backend.c.analyze.CDependencyListener;
 import org.teavm.backend.c.generate.BufferedCodeWriter;
@@ -51,6 +52,7 @@ import org.teavm.backend.c.intrinsic.FunctionIntrinsic;
 import org.teavm.backend.c.intrinsic.GCIntrinsic;
 import org.teavm.backend.c.intrinsic.IntegerIntrinsic;
 import org.teavm.backend.c.intrinsic.Intrinsic;
+import org.teavm.backend.c.intrinsic.IntrinsicContext;
 import org.teavm.backend.c.intrinsic.IntrinsicFactory;
 import org.teavm.backend.c.intrinsic.LongIntrinsic;
 import org.teavm.backend.c.intrinsic.MutatorIntrinsic;
@@ -61,6 +63,7 @@ import org.teavm.backend.c.intrinsic.PlatformObjectIntrinsic;
 import org.teavm.backend.c.intrinsic.RuntimeClassIntrinsic;
 import org.teavm.backend.c.intrinsic.ShadowStackIntrinsic;
 import org.teavm.backend.c.intrinsic.StructureIntrinsic;
+import org.teavm.backend.lowlevel.transform.CoroutineTransformation;
 import org.teavm.dependency.ClassDependency;
 import org.teavm.dependency.DependencyAnalyzer;
 import org.teavm.dependency.DependencyListener;
@@ -96,8 +99,11 @@ import org.teavm.model.lowlevel.NullCheckTransformation;
 import org.teavm.model.lowlevel.ShadowStackTransformer;
 import org.teavm.model.transformation.ClassInitializerInsertionTransformer;
 import org.teavm.model.transformation.ClassPatch;
+import org.teavm.model.util.AsyncMethodFinder;
 import org.teavm.runtime.Allocator;
+import org.teavm.runtime.EventQueue;
 import org.teavm.runtime.ExceptionHandling;
+import org.teavm.runtime.Fiber;
 import org.teavm.runtime.RuntimeArray;
 import org.teavm.runtime.RuntimeClass;
 import org.teavm.runtime.RuntimeObject;
@@ -121,6 +127,7 @@ public class CTarget implements TeaVMTarget, TeaVMCHost {
     private ExportDependencyListener exportDependencyListener = new ExportDependencyListener();
     private int minHeapSize = 32 * 1024 * 1024;
     private List<IntrinsicFactory> intrinsicFactories = new ArrayList<>();
+    private Set<MethodReference> asyncMethods;
 
     public void setMinHeapSize(int minHeapSize) {
         this.minHeapSize = minHeapSize;
@@ -201,6 +208,30 @@ public class CTarget implements TeaVMTarget, TeaVMCHost {
                 dependencyAnalyzer.linkField(field.getReference());
             }
         }
+
+        dependencyAnalyzer.linkMethod(new MethodReference(Fiber.class, "isResuming", boolean.class)).use();
+        dependencyAnalyzer.linkMethod(new MethodReference(Fiber.class, "isSuspending", boolean.class)).use();
+        dependencyAnalyzer.linkMethod(new MethodReference(Fiber.class, "current", Fiber.class)).use();
+        dependencyAnalyzer.linkMethod(new MethodReference(Fiber.class, "startMain", void.class)).use();
+        dependencyAnalyzer.linkMethod(new MethodReference(EventQueue.class, "process", void.class)).use();
+        dependencyAnalyzer.linkMethod(new MethodReference(Thread.class, "setCurrentThread", Thread.class,
+                void.class)).use();
+
+        ClassReader fiberClass = dependencyAnalyzer.getClassSource().get(Fiber.class.getName());
+        for (MethodReader method : fiberClass.getMethods()) {
+            if (method.getName().startsWith("pop") || method.getName().equals("push")) {
+                dependencyAnalyzer.linkMethod(method.getReference()).use();
+            }
+        }
+    }
+
+    @Override
+    public void analyzeBeforeOptimizations(ListableClassReaderSource classSource) {
+        AsyncMethodFinder asyncFinder = new AsyncMethodFinder(controller.getDependencyInfo().getCallGraph(),
+                controller.getDiagnostics());
+        asyncFinder.find(classSource);
+        asyncMethods = new HashSet<>(asyncFinder.getAsyncMethods());
+        asyncMethods.addAll(asyncFinder.getAsyncFamilyMethods());
     }
 
     @Override
@@ -214,6 +245,8 @@ public class CTarget implements TeaVMTarget, TeaVMCHost {
         classInitializerEliminator.apply(program);
         classInitializerTransformer.transform(program);
         nullCheckTransformation.apply(program, method.getResultType());
+        new CoroutineTransformation(controller.getUnprocessedClassSource(), asyncMethods)
+                .apply(program, method.getReference());
         shadowStackTransformer.apply(program, method);
     }
 
@@ -242,6 +275,7 @@ public class CTarget implements TeaVMTarget, TeaVMCHost {
         intrinsics.add(new ExceptionHandlingIntrinsic());
         intrinsics.add(new FunctionIntrinsic(characteristics, exportDependencyListener.getResolvedMethods()));
         intrinsics.add(new RuntimeClassIntrinsic());
+        intrinsics.add(new FiberIntrinsic());
         intrinsics.add(new LongIntrinsic());
         intrinsics.add(new IntegerIntrinsic());
 
@@ -250,7 +284,7 @@ public class CTarget implements TeaVMTarget, TeaVMCHost {
 
         GenerationContext context = new GenerationContext(vtableProvider, characteristics,
                 controller.getDependencyInfo(), stringPool, nameProvider, controller.getDiagnostics(), classes,
-                intrinsics, generators);
+                intrinsics, generators, asyncMethods::contains);
 
         BufferedCodeWriter codeWriter = new BufferedCodeWriter();
         copyResource(codeWriter, "runtime.c");
@@ -425,7 +459,7 @@ public class CTarget implements TeaVMTarget, TeaVMCHost {
         writer.println("initStaticFields();");
         generateStaticInitializerCalls(context, writer, classes);
         writer.println(context.getNames().forClassInitializer("java.lang.String") + "();");
-        generateCallToMainMethod(context, writer);
+        generateFiberStart(context, writer);
 
         writer.outdent().println("}");
     }
@@ -481,10 +515,49 @@ public class CTarget implements TeaVMTarget, TeaVMCHost {
         writer.outdent().println("}");
     }
 
-    private void generateCallToMainMethod(GenerationContext context, CodeWriter writer) {
+    private void generateFiberStart(GenerationContext context, CodeWriter writer) {
+        String startName = context.getNames().forMethod(new MethodReference(Fiber.class, "startMain", void.class));
+        String processName = context.getNames().forMethod(new MethodReference(EventQueue.class, "process", void.class));
+        writer.println(startName + "();");
+        writer.println(processName + "();");
+    }
+
+    class FiberIntrinsic implements Intrinsic {
+        @Override
+        public boolean canHandle(MethodReference method) {
+            if (!method.getClassName().equals(Fiber.class.getName())) {
+                return false;
+            }
+            switch (method.getName()) {
+                case "runMain":
+                case "setCurrentThread":
+                    return true;
+                default:
+                    return false;
+            }
+        }
+
+        @Override
+        public void apply(IntrinsicContext context, InvocationExpr invocation) {
+            switch (invocation.getMethod().getName()) {
+                case "runMain":
+                    generateCallToMainMethod(context.names(), context.writer());
+                    break;
+                case "setCurrentThread":
+                    String methodName = context.names().forMethod(new MethodReference(Thread.class,
+                            "setCurrentThread", Thread.class, void.class));
+                    context.writer().print(methodName).print("(");
+                    context.emit(invocation.getArguments().get(0));
+                    context.writer().print(")");
+                    break;
+            }
+        }
+    }
+
+    private void generateCallToMainMethod(NameProvider names, CodeWriter writer) {
         TeaVMEntryPoint entryPoint = controller.getEntryPoints().get("main");
         if (entryPoint != null) {
-            String mainMethod = context.getNames().forMethod(entryPoint.getMethod());
+            String mainMethod = names.forMethod(entryPoint.getMethod());
             writer.println(mainMethod + "(NULL);");
         }
     }
@@ -496,6 +569,6 @@ public class CTarget implements TeaVMTarget, TeaVMCHost {
 
     @Override
     public boolean isAsyncSupported() {
-        return false;
+        return true;
     }
 }

core/src/main/java/org/teavm/backend/c/generate/ClassGenerator.java

@@ -194,7 +194,6 @@ public class ClassGenerator {
         codeGenerator.generateMethodSignature(forwardDeclarationsWriter, method.getReference(),
                 method.hasModifier(ElementModifier.STATIC), false);
         forwardDeclarationsWriter.println(";");
-
     }
 
     private void generateInitializer(ClassHolder cls) {

core/src/main/java/org/teavm/backend/c/generate/CodeGenerationVisitor.java

@@ -65,14 +65,17 @@ import org.teavm.model.AnnotationReader;
 import org.teavm.model.AnnotationValue;
 import org.teavm.model.ClassReader;
 import org.teavm.model.ElementModifier;
+import org.teavm.model.FieldReference;
 import org.teavm.model.MethodReader;
 import org.teavm.model.MethodReference;
 import org.teavm.model.ValueType;
 import org.teavm.model.classes.VirtualTable;
 import org.teavm.runtime.Allocator;
 import org.teavm.runtime.ExceptionHandling;
+import org.teavm.runtime.Fiber;
 import org.teavm.runtime.RuntimeArray;
 import org.teavm.runtime.RuntimeClass;
+import org.teavm.runtime.RuntimeObject;
 
 public class CodeGenerationVisitor implements ExprVisitor, StatementVisitor {
     private static final MethodReference ALLOC_METHOD = new MethodReference(Allocator.class,
@@ -83,6 +86,14 @@ public class CodeGenerationVisitor implements ExprVisitor, StatementVisitor {
             "allocateMultiArray", RuntimeClass.class, Address.class, int.class, RuntimeArray.class);
     private static final MethodReference THROW_EXCEPTION_METHOD = new MethodReference(ExceptionHandling.class,
             "throwException", Throwable.class, void.class);
+    private static final MethodReference MONITOR_ENTER = new MethodReference(Object.class, "monitorEnter",
+            Object.class, void.class);
+    private static final MethodReference MONITOR_EXIT = new MethodReference(Object.class, "monitorExit",
+            Object.class, void.class);
+    private static final MethodReference MONITOR_ENTER_SYNC = new MethodReference(Object.class, "monitorEnterSync",
+            Object.class, void.class);
+    private static final MethodReference MONITOR_EXIT_SYNC = new MethodReference(Object.class, "monitorExitSync",
+            Object.class, void.class);
 
     private GenerationContext context;
     private NameProvider names;
@@ -91,6 +102,9 @@ public class CodeGenerationVisitor implements ExprVisitor, StatementVisitor {
     private int[] maxTemporaryVariableLevel = new int[5];
     private MethodReference callingMethod;
     private Set<? super String> includes;
+    private int currentPart;
+    private boolean end;
+    private boolean async;
 
     public CodeGenerationVisitor(GenerationContext context, CodeWriter writer, Set<? super String> includes) {
         this.context = context;
@@ -99,6 +113,10 @@ public class CodeGenerationVisitor implements ExprVisitor, StatementVisitor {
         this.includes = includes;
     }
 
+    public void setAsync(boolean async) {
+        this.async = async;
+    }
+
     public int[] getTemporaries() {
         return maxTemporaryVariableLevel;
     }
@@ -539,16 +557,31 @@ public class CodeGenerationVisitor implements ExprVisitor, StatementVisitor {
 
     @Override
     public void visit(QualificationExpr expr) {
+        FieldReference field = expr.getField();
+        if (isMonitorField(field)) {
+            String tmp = allocTemporaryVariable(CVariableType.INT);
+            writer.print("(" + tmp + " = FIELD(");
+            expr.getQualified().acceptVisitor(this);
+            field = new FieldReference(RuntimeObject.class.getName(), "hashCode");
+            writer.print(", ").print(names.forClass(field.getClassName()) + ", "
+                    + names.forMemberField(field) + ")");
+            writer.print(", UNPACK_MONITOR(" + tmp + "))");
+            return;
+        }
+
         if (expr.getQualified() != null) {
             writer.print("FIELD(");
             expr.getQualified().acceptVisitor(this);
-            writer.print(", ").print(names.forClass(expr.getField().getClassName()) + ", "
+            writer.print(", ").print(names.forClass(field.getClassName()) + ", " + names.forMemberField(field) + ")");
-                    + names.forMemberField(expr.getField()) + ")");
         } else {
-            writer.print(names.forStaticField(expr.getField()));
+            writer.print(names.forStaticField(field));
         }
     }
 
+    private boolean isMonitorField(FieldReference field) {
+        return field.getClassName().equals("java.lang.Object") && field.getFieldName().equals("monitor");
+    }
+
     @Override
     public void visit(NewExpr expr) {
         allocObject(expr.getConstructedClass());
@@ -630,11 +663,30 @@ public class CodeGenerationVisitor implements ExprVisitor, StatementVisitor {
     @Override
     public void visit(AssignmentStatement statement) {
         if (statement.getLeftValue() != null) {
+            if (statement.getLeftValue() instanceof QualificationExpr) {
+                QualificationExpr qualification = (QualificationExpr) statement.getLeftValue();
+                FieldReference field = qualification.getField();
+                if (isMonitorField(field)) {
+                    writer.print("FIELD(");
+                    qualification.getQualified().acceptVisitor(this);
+                    field = new FieldReference(RuntimeObject.class.getName(), "hashCode");
+                    writer.print(", ").print(names.forClass(field.getClassName()) + ", "
+                            + names.forMemberField(field) + ") = PACK_MONITOR(");
+                    statement.getRightValue().acceptVisitor(this);
+                    writer.println(");");
+                    return;
+                }
+            }
+
             statement.getLeftValue().acceptVisitor(this);
             writer.print(" = ");
         }
         statement.getRightValue().acceptVisitor(this);
         writer.println(";");
+
+        if (statement.isAsync()) {
+            emitSuspendChecker();
+        }
     }
 
     @Override
@@ -643,9 +695,17 @@ public class CodeGenerationVisitor implements ExprVisitor, StatementVisitor {
     }
 
     private void visitMany(List<Statement> statements) {
-        for (Statement statement : statements) {
+        if (statements.isEmpty()) {
-            statement.acceptVisitor(this);
+            return;
         }
+        boolean oldEnd = end;
+        for (int i = 0; i < statements.size() - 1; ++i) {
+            end = false;
+            statements.get(i).acceptVisitor(this);
+        }
+        end = oldEnd;
+        statements.get(statements.size() - 1).acceptVisitor(this);
+        end = oldEnd;
     }
 
     @Override
@@ -688,8 +748,12 @@ public class CodeGenerationVisitor implements ExprVisitor, StatementVisitor {
             }
 
             writer.indent();
-            visitMany(clause.getBody());
+            boolean oldEnd = end;
-            writer.println("break;");
+            for (Statement part : clause.getBody()) {
+                end = false;
+                part.acceptVisitor(this);
+            }
+            end = oldEnd;
             writer.outdent();
         }
 
@@ -716,7 +780,12 @@ public class CodeGenerationVisitor implements ExprVisitor, StatementVisitor {
         }
         writer.println(") {").indent();
 
-        visitMany(statement.getBody());
+        boolean oldEnd = end;
+        for (Statement part : statement.getBody()) {
+            end = false;
+            part.acceptVisitor(this);
+        }
+        end = oldEnd;
 
         if (statement.getId() != null) {
             writer.outdent().println("cnt_" + statement.getId() + ":;").indent();
@@ -779,7 +848,6 @@ public class CodeGenerationVisitor implements ExprVisitor, StatementVisitor {
 
     @Override
     public void visit(TryCatchStatement statement) {
-
     }
 
     @Override
@@ -788,10 +856,21 @@ public class CodeGenerationVisitor implements ExprVisitor, StatementVisitor {
 
     @Override
     public void visit(MonitorEnterStatement statement) {
+        writer.print(names.forMethod(async ? MONITOR_ENTER : MONITOR_ENTER_SYNC)).print("(");
+        statement.getObjectRef().acceptVisitor(this);
+        writer.println(");");
     }
 
     @Override
     public void visit(MonitorExitStatement statement) {
+        writer.print(names.forMethod(async ? MONITOR_EXIT : MONITOR_EXIT_SYNC)).print("(");
+        statement.getObjectRef().acceptVisitor(this);
+        writer.println(");");
+    }
+
+    public void emitSuspendChecker() {
+        String suspendingName = names.forMethod(new MethodReference(Fiber.class, "isSuspending", boolean.class));
+        writer.println("if (" + suspendingName + "(fiber)) goto exit_loop;");
     }
 
     private IntrinsicContext intrinsicContext = new IntrinsicContext() {

core/src/main/java/org/teavm/backend/c/generate/CodeGenerator.java

@@ -16,6 +16,7 @@
 package org.teavm.backend.c.generate;
 
 import java.util.Set;
+import org.teavm.ast.MethodNode;
 import org.teavm.ast.RegularMethodNode;
 import org.teavm.ast.VariableNode;
 import org.teavm.model.ElementModifier;
@@ -43,16 +44,21 @@ public class CodeGenerator {
         writer.print(" {").indent().println();
 
         localsWriter = writer.fragment();
-
+        CodeGenerationVisitor visitor = generateMethodBody(methodNode);
-        CodeGenerationVisitor visitor = new CodeGenerationVisitor(context, writer, includes);
-        visitor.setCallingMethod(methodNode.getReference());
-        methodNode.getBody().acceptVisitor(visitor);
-
         generateLocals(methodNode, visitor.getTemporaries());
 
         writer.outdent().println("}");
     }
 
+
+    private CodeGenerationVisitor generateMethodBody(RegularMethodNode methodNode) {
+        CodeGenerationVisitor visitor = new CodeGenerationVisitor(context, writer, includes);
+        visitor.setAsync(context.isAsync(methodNode.getReference()));
+        visitor.setCallingMethod(methodNode.getReference());
+        methodNode.getBody().acceptVisitor(visitor);
+        return visitor;
+    }
+
     public void generateMethodSignature(CodeWriter writer, MethodReference methodRef, boolean isStatic,
             boolean withNames) {
         writer.print("static ");
@@ -91,7 +97,7 @@ public class CodeGenerator {
         }
     }
 
-    private void generateLocals(RegularMethodNode methodNode, int[] temporaryCount) {
+    private void generateLocals(MethodNode methodNode, int[] temporaryCount) {
         int start = methodNode.getReference().parameterCount() + 1;
         for (int i = start; i < methodNode.getVariables().size(); ++i) {
             VariableNode variableNode = methodNode.getVariables().get(i);

core/src/main/java/org/teavm/backend/c/generate/GenerationContext.java

@@ -19,6 +19,7 @@ import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.function.Predicate;
 import org.teavm.backend.c.generators.Generator;
 import org.teavm.backend.c.intrinsic.Intrinsic;
 import org.teavm.dependency.DependencyInfo;
@@ -39,10 +40,12 @@ public class GenerationContext {
     private List<Intrinsic> intrinsics;
     private List<Generator> generators;
     private Map<MethodReference, Intrinsic> intrinsicCache = new HashMap<>();
+    private Predicate<MethodReference> asyncMethods;
 
     public GenerationContext(VirtualTableProvider virtualTableProvider, Characteristics characteristics,
             DependencyInfo dependencies, StringPool stringPool, NameProvider names, Diagnostics diagnostics,
-            ClassReaderSource classSource, List<Intrinsic> intrinsics, List<Generator> generators) {
+            ClassReaderSource classSource, List<Intrinsic> intrinsics, List<Generator> generators,
+            Predicate<MethodReference> asyncMethods) {
         this.virtualTableProvider = virtualTableProvider;
         this.characteristics = characteristics;
         this.dependencies = dependencies;
@@ -52,6 +55,7 @@ public class GenerationContext {
         this.classSource = classSource;
         this.intrinsics = new ArrayList<>(intrinsics);
         this.generators = new ArrayList<>(generators);
+        this.asyncMethods = asyncMethods;
     }
 
     public void addIntrinsic(Intrinsic intrinsic) {
@@ -99,4 +103,8 @@ public class GenerationContext {
         }
         return null;
     }
+
+    public boolean isAsync(MethodReference method) {
+        return asyncMethods.test(method);
+    }
 }

core/src/main/java/org/teavm/backend/c/intrinsic/PlatformIntrinsic.java

@@ -30,7 +30,6 @@ public class PlatformIntrinsic implements Intrinsic {
         switch (method.getName()) {
             case "getPlatformObject":
             case "asJavaClass":
-            case "createQueue":
                 return true;
         }
         return false;
@@ -43,9 +42,6 @@ public class PlatformIntrinsic implements Intrinsic {
             case "asJavaClass":
                 context.emit(invocation.getArguments().get(0));
                 break;
-            case "createQueue":
-                context.writer().print("NULL");
-                break;
         }
     }
 }

core/src/main/java/org/teavm/backend/lowlevel/transform/CoroutineTransformation.java

@@ -0,0 +1,502 @@
+/*
+ *  Copyright 2018 Alexey Andreev.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.teavm.backend.lowlevel.transform;
+
+import com.carrotsearch.hppc.IntIntHashMap;
+import com.carrotsearch.hppc.IntIntMap;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.BitSet;
+import java.util.Collections;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import org.teavm.common.Graph;
+import org.teavm.common.GraphSplittingBackend;
+import org.teavm.common.GraphUtils;
+import org.teavm.model.BasicBlock;
+import org.teavm.model.ClassReader;
+import org.teavm.model.ClassReaderSource;
+import org.teavm.model.Instruction;
+import org.teavm.model.MethodDescriptor;
+import org.teavm.model.MethodReader;
+import org.teavm.model.MethodReference;
+import org.teavm.model.Program;
+import org.teavm.model.TextLocation;
+import org.teavm.model.TryCatchBlock;
+import org.teavm.model.ValueType;
+import org.teavm.model.Variable;
+import org.teavm.model.instructions.BranchingCondition;
+import org.teavm.model.instructions.BranchingInstruction;
+import org.teavm.model.instructions.DoubleConstantInstruction;
+import org.teavm.model.instructions.ExitInstruction;
+import org.teavm.model.instructions.FloatConstantInstruction;
+import org.teavm.model.instructions.InitClassInstruction;
+import org.teavm.model.instructions.IntegerConstantInstruction;
+import org.teavm.model.instructions.InvocationType;
+import org.teavm.model.instructions.InvokeInstruction;
+import org.teavm.model.instructions.JumpInstruction;
+import org.teavm.model.instructions.LongConstantInstruction;
+import org.teavm.model.instructions.MonitorEnterInstruction;
+import org.teavm.model.instructions.NullConstantInstruction;
+import org.teavm.model.instructions.SwitchInstruction;
+import org.teavm.model.instructions.SwitchTableEntry;
+import org.teavm.model.util.BasicBlockMapper;
+import org.teavm.model.util.BasicBlockSplitter;
+import org.teavm.model.util.DefinitionExtractor;
+import org.teavm.model.util.LivenessAnalyzer;
+import org.teavm.model.util.PhiUpdater;
+import org.teavm.model.util.ProgramUtils;
+import org.teavm.model.util.TransitionExtractor;
+import org.teavm.model.util.TypeInferer;
+import org.teavm.model.util.UsageExtractor;
+import org.teavm.model.util.VariableType;
+import org.teavm.runtime.Fiber;
+
+public class CoroutineTransformation {
+    private ClassReaderSource classSource;
+    private LivenessAnalyzer livenessAnalysis = new LivenessAnalyzer();
+    private TypeInferer variableTypes = new TypeInferer();
+    private Set<MethodReference> asyncMethods;
+    private Program program;
+    private Variable fiberVar;
+    private BasicBlockSplitter splitter;
+    private SwitchInstruction resumeSwitch;
+    private int parameterCount;
+    private ValueType returnType;
+
+    public CoroutineTransformation(ClassReaderSource classSource, Set<MethodReference> asyncMethods) {
+        this.classSource = classSource;
+        this.asyncMethods = asyncMethods;
+    }
+
+    public void apply(Program program, MethodReference methodReference) {
+        if (methodReference.getClassName().equals(Fiber.class.getName())) {
+            return;
+        }
+
+        boolean hasJob = false;
+        for (BasicBlock block : program.getBasicBlocks()) {
+            if (hasSplitInstructions(block)) {
+                hasJob = true;
+            }
+        }
+        if (!hasJob) {
+            return;
+        }
+
+        this.program = program;
+        parameterCount = methodReference.parameterCount();
+        returnType = methodReference.getReturnType();
+        variableTypes.inferTypes(program, methodReference);
+        livenessAnalysis.analyze(program);
+        splitter = new BasicBlockSplitter(program);
+        int basicBlockCount = program.basicBlockCount();
+        createSplitPrologue();
+        for (int i = 1; i <= basicBlockCount; ++i) {
+            processBlock(program.basicBlockAt(i));
+        }
+        splitter.fixProgram();
+        processIrreducibleCfg();
+    }
+
+    private void createSplitPrologue() {
+        fiberVar = program.createVariable();
+        fiberVar.setLabel("fiber");
+
+        BasicBlock firstBlock = program.basicBlockAt(0);
+        BasicBlock continueBlock = splitter.split(firstBlock, null);
+        BasicBlock switchStateBlock = program.createBasicBlock();
+        TextLocation location = continueBlock.getFirstInstruction().getLocation();
+
+        InvokeInstruction getFiber = new InvokeInstruction();
+        getFiber.setType(InvocationType.SPECIAL);
+        getFiber.setMethod(new MethodReference(Fiber.class, "current", Fiber.class));
+        getFiber.setReceiver(fiberVar);
+        getFiber.setLocation(location);
+        firstBlock.add(getFiber);
+
+        InvokeInstruction isResuming = new InvokeInstruction();
+        isResuming.setType(InvocationType.SPECIAL);
+        isResuming.setMethod(new MethodReference(Fiber.class, "isResuming", boolean.class));
+        isResuming.setInstance(fiberVar);
+        isResuming.setReceiver(program.createVariable());
+        isResuming.setLocation(location);
+        firstBlock.add(isResuming);
+
+        BranchingInstruction jumpIfResuming = new BranchingInstruction(BranchingCondition.NOT_EQUAL);
+        jumpIfResuming.setOperand(isResuming.getReceiver());
+        jumpIfResuming.setConsequent(switchStateBlock);
+        jumpIfResuming.setAlternative(continueBlock);
+        firstBlock.add(jumpIfResuming);
+
+        InvokeInstruction popInt = new InvokeInstruction();
+        popInt.setType(InvocationType.SPECIAL);
+        popInt.setMethod(new MethodReference(Fiber.class, "popInt", int.class));
+        popInt.setInstance(fiberVar);
+        popInt.setReceiver(program.createVariable());
+        popInt.setLocation(location);
+        switchStateBlock.add(popInt);
+
+        resumeSwitch = new SwitchInstruction();
+        resumeSwitch.setDefaultTarget(continueBlock);
+        resumeSwitch.setCondition(popInt.getReceiver());
+        resumeSwitch.setLocation(location);
+        switchStateBlock.add(resumeSwitch);
+    }
+
+    private void processBlock(BasicBlock block) {
+        Map<Instruction, BitSet> splitInstructions = collectSplitInstructions(block);
+        List<Instruction> instructionList = new ArrayList<>(splitInstructions.keySet());
+        Collections.reverse(instructionList);
+        for (Instruction instruction : instructionList) {
+            BasicBlock intermediate = splitter.split(block, instruction.getPrevious());
+            BasicBlock next = splitter.split(intermediate, instruction);
+            createSplitPoint(block, intermediate, next, splitInstructions.get(instruction));
+            block = next;
+        }
+    }
+
+    private Map<Instruction, BitSet> collectSplitInstructions(BasicBlock block) {
+        if (!hasSplitInstructions(block)) {
+            return Collections.emptyMap();
+        }
+
+        BitSet live = new BitSet();
+        TransitionExtractor transitionExtractor = new TransitionExtractor();
+        block.getLastInstruction().acceptVisitor(transitionExtractor);
+        for (BasicBlock successor : transitionExtractor.getTargets()) {
+            live.or(livenessAnalysis.liveIn(successor.getIndex()));
+        }
+        for (TryCatchBlock tryCatch : block.getTryCatchBlocks()) {
+            live.or(livenessAnalysis.liveIn(tryCatch.getHandler().getIndex()));
+        }
+
+        Map<Instruction, BitSet> result = new LinkedHashMap<>();
+        UsageExtractor use = new UsageExtractor();
+        DefinitionExtractor def = new DefinitionExtractor();
+        for (Instruction instruction = block.getLastInstruction(); instruction != null;
+                instruction = instruction.getPrevious()) {
+            instruction.acceptVisitor(def);
+            if (def.getDefinedVariables() != null) {
+                for (Variable var : def.getDefinedVariables()) {
+                    live.clear(var.getIndex());
+                }
+            }
+            instruction.acceptVisitor(use);
+            if (use.getUsedVariables() != null) {
+                for (Variable var : use.getUsedVariables()) {
+                    live.set(var.getIndex());
+                }
+            }
+
+            if (isSplitInstruction(instruction)) {
+                result.put(instruction, (BitSet) live.clone());
+            }
+        }
+        return result;
+    }
+
+    private boolean hasSplitInstructions(BasicBlock block) {
+        for (Instruction instruction : block) {
+            if (isSplitInstruction(instruction)) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    private boolean isSplitInstruction(Instruction instruction) {
+        if (instruction instanceof InvokeInstruction) {
+            InvokeInstruction invoke = (InvokeInstruction) instruction;
+            MethodReference method = findRealMethod(invoke.getMethod());
+            if (method.getClassName().equals(Fiber.class.getName())) {
+                return false;
+            }
+            return asyncMethods.contains(method);
+        } else if (instruction instanceof InitClassInstruction) {
+            return isSplittingClassInitializer(((InitClassInstruction) instruction).getClassName());
+        } else {
+            return instruction instanceof MonitorEnterInstruction;
+        }
+    }
+
+    private void createSplitPoint(BasicBlock block, BasicBlock intermediate, BasicBlock next, BitSet liveVars) {
+        int stateNumber = resumeSwitch.getEntries().size();
+        Instruction splitInstruction = intermediate.getFirstInstruction();
+
+        JumpInstruction jumpToIntermediate = new JumpInstruction();
+        jumpToIntermediate.setTarget(intermediate);
+        jumpToIntermediate.setLocation(splitInstruction.getLocation());
+        block.add(jumpToIntermediate);
+
+        BasicBlock restoreBlock = program.createBasicBlock();
+        BasicBlock saveBlock = program.createBasicBlock();
+
+        SwitchTableEntry switchTableEntry = new SwitchTableEntry();
+        switchTableEntry.setCondition(stateNumber);
+        switchTableEntry.setTarget(restoreBlock);
+        resumeSwitch.getEntries().add(switchTableEntry);
+
+        InvokeInstruction isSuspending = new InvokeInstruction();
+        isSuspending.setType(InvocationType.SPECIAL);
+        isSuspending.setMethod(new MethodReference(Fiber.class, "isSuspending", boolean.class));
+        isSuspending.setInstance(fiberVar);
+        isSuspending.setReceiver(program.createVariable());
+        isSuspending.setLocation(splitInstruction.getLocation());
+        intermediate.add(isSuspending);
+
+        BranchingInstruction branchIfSuspending = new BranchingInstruction(BranchingCondition.NOT_EQUAL);
+        branchIfSuspending.setOperand(isSuspending.getReceiver());
+        branchIfSuspending.setConsequent(saveBlock);
+        branchIfSuspending.setAlternative(next);
+        branchIfSuspending.setLocation(splitInstruction.getLocation());
+        intermediate.add(branchIfSuspending);
+
+        restoreBlock.addAll(restoreState(liveVars));
+        JumpInstruction doneRestoring = new JumpInstruction();
+        doneRestoring.setTarget(intermediate);
+        restoreBlock.add(doneRestoring);
+        for (Instruction instruction : restoreBlock) {
+            instruction.setLocation(splitInstruction.getLocation());
+        }
+
+        for (Instruction instruction : saveState(liveVars)) {
+            instruction.setLocation(splitInstruction.getLocation());
+            saveBlock.add(instruction);
+        }
+        for (Instruction instruction : saveStateNumber(stateNumber)) {
+            instruction.setLocation(splitInstruction.getLocation());
+            saveBlock.add(instruction);
+        }
+        createReturnInstructions(splitInstruction.getLocation(), saveBlock);
+    }
+
+    private List<Instruction> saveState(BitSet vars) {
+        List<Instruction> instructions = new ArrayList<>();
+        for (int var = vars.nextSetBit(0); var >= 0; var = vars.nextSetBit(var + 1)) {
+            saveVariable(var, instructions);
+        }
+
+        return instructions;
+    }
+
+    private List<Instruction> saveStateNumber(int number) {
+        IntegerConstantInstruction constant = new IntegerConstantInstruction();
+        constant.setReceiver(program.createVariable());
+        constant.setConstant(number);
+
+        InvokeInstruction invoke = new InvokeInstruction();
+        invoke.setType(InvocationType.SPECIAL);
+        invoke.setMethod(new MethodReference(Fiber.class, "push", int.class, void.class));
+        invoke.setInstance(fiberVar);
+        invoke.setArguments(constant.getReceiver());
+
+        return Arrays.asList(constant, invoke);
+    }
+
+    private List<Instruction> restoreState(BitSet vars) {
+        List<Instruction> instructions = new ArrayList<>();
+        int[] varArray = new int[vars.cardinality()];
+        int j = 0;
+        for (int i = vars.nextSetBit(0); i >= 0; i = vars.nextSetBit(i + 1)) {
+            varArray[j++] = i;
+        }
+
+        for (int i = varArray.length - 1; i >= 0; --i) {
+            restoreVariable(varArray[i], instructions);
+        }
+
+        return instructions;
+    }
+
+    private void saveVariable(int var, List<Instruction> instructions) {
+        VariableType type = variableTypes.typeOf(var);
+        InvokeInstruction invoke = new InvokeInstruction();
+        invoke.setType(InvocationType.SPECIAL);
+        invoke.setInstance(fiberVar);
+        invoke.setArguments(program.variableAt(var));
+
+        switch (type) {
+            case INT:
+                invoke.setMethod(new MethodReference(Fiber.class, "push", int.class, void.class));
+                break;
+            case LONG:
+                invoke.setMethod(new MethodReference(Fiber.class, "push", long.class, void.class));
+                break;
+            case FLOAT:
+                invoke.setMethod(new MethodReference(Fiber.class, "push", float.class, void.class));
+                break;
+            case DOUBLE:
+                invoke.setMethod(new MethodReference(Fiber.class, "push", double.class, void.class));
+                break;
+            default:
+                invoke.setMethod(new MethodReference(Fiber.class, "push", Object.class, void.class));
+                break;
+        }
+
+        instructions.add(invoke);
+    }
+
+    private void restoreVariable(int var, List<Instruction> instructions) {
+        VariableType type = variableTypes.typeOf(var);
+        InvokeInstruction invoke = new InvokeInstruction();
+        invoke.setType(InvocationType.SPECIAL);
+        invoke.setInstance(fiberVar);
+        invoke.setReceiver(program.variableAt(var));
+
+        switch (type) {
+            case INT:
+                invoke.setMethod(new MethodReference(Fiber.class, "popInt", int.class));
+                break;
+            case LONG:
+                invoke.setMethod(new MethodReference(Fiber.class, "popLong", long.class));
+                break;
+            case FLOAT:
+                invoke.setMethod(new MethodReference(Fiber.class, "popFloat", float.class));
+                break;
+            case DOUBLE:
+                invoke.setMethod(new MethodReference(Fiber.class, "popDouble", double.class));
+                break;
+            default:
+                invoke.setMethod(new MethodReference(Fiber.class, "popObject", Object.class));
+                break;
+        }
+
+        instructions.add(invoke);
+    }
+
+    private boolean isSplittingClassInitializer(String className) {
+        ClassReader cls = classSource.get(className);
+        if (cls == null) {
+            return false;
+        }
+
+        MethodReader method = cls.getMethod(new MethodDescriptor("<clinit>", ValueType.VOID));
+        return method != null && asyncMethods.contains(method.getReference());
+    }
+
+    private MethodReference findRealMethod(MethodReference method) {
+        String clsName = method.getClassName();
+        while (clsName != null) {
+            ClassReader cls = classSource.get(clsName);
+            if (cls == null) {
+                break;
+            }
+            MethodReader methodReader = cls.getMethod(method.getDescriptor());
+            if (methodReader != null) {
+                return new MethodReference(clsName, method.getDescriptor());
+            }
+            clsName = cls.getParent();
+            if (clsName != null && clsName.equals(cls.getName())) {
+                break;
+            }
+        }
+        return method;
+    }
+
+    private void createReturnInstructions(TextLocation location, BasicBlock block) {
+        ExitInstruction exit = new ExitInstruction();
+        exit.setLocation(location);
+        if (returnType == ValueType.VOID) {
+            block.add(exit);
+            return;
+        }
+        exit.setValueToReturn(program.createVariable());
+        Instruction returnValue = createReturnValueInstruction(exit.getValueToReturn());
+        returnValue.setLocation(location);
+        block.add(returnValue);
+        block.add(exit);
+    }
+
+    private Instruction createReturnValueInstruction(Variable target) {
+        if (returnType instanceof ValueType.Primitive) {
+            switch (((ValueType.Primitive) returnType).getKind()) {
+                case BOOLEAN:
+                case BYTE:
+                case CHARACTER:
+                case SHORT:
+                case INTEGER: {
+                    IntegerConstantInstruction instruction = new IntegerConstantInstruction();
+                    instruction.setReceiver(target);
+                    return instruction;
+                }
+                case LONG: {
+                    LongConstantInstruction instruction = new LongConstantInstruction();
+                    instruction.setReceiver(target);
+                    return instruction;
+                }
+                case FLOAT: {
+                    FloatConstantInstruction instruction = new FloatConstantInstruction();
+                    instruction.setReceiver(target);
+                    return instruction;
+                }
+                case DOUBLE: {
+                    DoubleConstantInstruction instruction = new DoubleConstantInstruction();
+                    instruction.setReceiver(target);
+                    return instruction;
+                }
+            }
+        }
+
+        NullConstantInstruction instruction = new NullConstantInstruction();
+        instruction.setReceiver(target);
+        return instruction;
+    }
+
+    private void processIrreducibleCfg() {
+        Graph graph = ProgramUtils.buildControlFlowGraph(program);
+        if (!GraphUtils.isIrreducible(graph)) {
+            return;
+        }
+
+        SplittingBackend splittingBackend = new SplittingBackend();
+        int[] weights = new int[graph.size()];
+        for (int i = 0; i < program.basicBlockCount(); ++i) {
+            weights[i] = program.basicBlockAt(i).instructionCount();
+        }
+        GraphUtils.splitIrreducibleGraph(graph, weights, splittingBackend);
+        new PhiUpdater().updatePhis(program, parameterCount + 1);
+    }
+
+    class SplittingBackend implements GraphSplittingBackend {
+        @Override
+        public int[] split(int[] domain, int[] nodes) {
+            int[] copies = new int[nodes.length];
+            IntIntMap map = new IntIntHashMap();
+            for (int i = 0; i < nodes.length; ++i) {
+                int node = nodes[i];
+                BasicBlock block = program.basicBlockAt(node);
+                BasicBlock blockCopy = program.createBasicBlock();
+                ProgramUtils.copyBasicBlock(block, blockCopy);
+                copies[i] = blockCopy.getIndex();
+                map.put(nodes[i], copies[i] + 1);
+            }
+            BasicBlockMapper copyBlockMapper = new BasicBlockMapper((int block) -> {
+                int mappedIndex = map.get(block);
+                return mappedIndex == 0 ? block : mappedIndex - 1;
+            });
+            for (int copy : copies) {
+                copyBlockMapper.transform(program.basicBlockAt(copy));
+            }
+            for (int domainNode : domain) {
+                copyBlockMapper.transform(program.basicBlockAt(domainNode));
+            }
+            return copies;
+        }
+    }
+}

core/src/main/java/org/teavm/model/lowlevel/ExceptionHandlingShadowStackContributor.java

@@ -51,6 +51,8 @@ import org.teavm.model.instructions.InvocationType;
 import org.teavm.model.instructions.InvokeInstruction;
 import org.teavm.model.instructions.JumpInstruction;
 import org.teavm.model.instructions.LongConstantInstruction;
+import org.teavm.model.instructions.MonitorEnterInstruction;
+import org.teavm.model.instructions.MonitorExitInstruction;
 import org.teavm.model.instructions.NullConstantInstruction;
 import org.teavm.model.instructions.RaiseInstruction;
 import org.teavm.model.instructions.SwitchInstruction;
@@ -258,7 +260,8 @@ public class ExceptionHandlingShadowStackContributor {
     private boolean isCallInstruction(Instruction insn) {
         if (insn instanceof InitClassInstruction || insn instanceof ConstructInstruction
                 || insn instanceof ConstructArrayInstruction || insn instanceof ConstructMultiArrayInstruction
-                || insn instanceof CloneArrayInstruction || insn instanceof RaiseInstruction) {
+                || insn instanceof CloneArrayInstruction || insn instanceof RaiseInstruction
+                || insn instanceof MonitorEnterInstruction || insn instanceof MonitorExitInstruction) {
             return true;
         } else if (insn instanceof InvokeInstruction) {
             MethodReference method = ((InvokeInstruction) insn).getMethod();

core/src/main/java/org/teavm/model/lowlevel/GCShadowStackContributor.java

@@ -50,6 +50,8 @@ import org.teavm.model.instructions.InitClassInstruction;
 import org.teavm.model.instructions.IntegerConstantInstruction;
 import org.teavm.model.instructions.InvocationType;
 import org.teavm.model.instructions.InvokeInstruction;
+import org.teavm.model.instructions.MonitorEnterInstruction;
+import org.teavm.model.instructions.MonitorExitInstruction;
 import org.teavm.model.instructions.RaiseInstruction;
 import org.teavm.model.util.DefinitionExtractor;
 import org.teavm.model.util.GraphColorer;
@@ -155,7 +157,8 @@ public class GCShadowStackContributor {
                 if (insn instanceof InvokeInstruction || insn instanceof InitClassInstruction
                         || insn instanceof ConstructInstruction || insn instanceof ConstructArrayInstruction
                         || insn instanceof ConstructMultiArrayInstruction
-                        || insn instanceof CloneArrayInstruction || insn instanceof RaiseInstruction) {
+                        || insn instanceof CloneArrayInstruction || insn instanceof RaiseInstruction
+                        || insn instanceof MonitorEnterInstruction || insn instanceof MonitorExitInstruction) {
                     if (insn instanceof InvokeInstruction
                             && !characteristics.isManaged(((InvokeInstruction) insn).getMethod())) {
                         continue;

core/src/main/java/org/teavm/model/util/AsyncMethodFinder.java

@@ -40,6 +40,7 @@ import org.teavm.model.MethodReference;
 import org.teavm.model.ProgramReader;
 import org.teavm.model.VariableReader;
 import org.teavm.model.instructions.AbstractInstructionReader;
+import org.teavm.runtime.Fiber;
 
 public class AsyncMethodFinder {
     private Set<MethodReference> asyncMethods = new HashSet<>();
@@ -142,6 +143,10 @@ public class AsyncMethodFinder {
     }
 
     private void add(MethodReference methodRef, CallStack stack) {
+        if (methodRef.getClassName().equals(Fiber.class.getName())) {
+            return;
+        }
+
         if (!asyncMethods.add(methodRef)) {
             return;
         }

core/src/main/java/org/teavm/model/util/BasicBlockSplitter.java

@@ -67,7 +67,7 @@ public class BasicBlockSplitter {
     public BasicBlock split(BasicBlock block, Instruction afterInstruction) {
         initIfNecessary();
 
-        if (afterInstruction.getBasicBlock() != block) {
+        if (afterInstruction != null && afterInstruction.getBasicBlock() != block) {
             throw new IllegalArgumentException();
         }
 
@@ -88,10 +88,18 @@ public class BasicBlockSplitter {
         isLastInSequence.add((byte) 1);
 
         splitBlock.getTryCatchBlocks().addAll(ProgramUtils.copyTryCatches(block, program));
-        while (afterInstruction.getNext() != null) {
+        if (afterInstruction != null) {
-            Instruction nextInstruction = afterInstruction.getNext();
+            while (afterInstruction.getNext() != null) {
-            nextInstruction.delete();
+                Instruction nextInstruction = afterInstruction.getNext();
-            splitBlock.add(nextInstruction);
+                nextInstruction.delete();
+                splitBlock.add(nextInstruction);
+            }
+        } else {
+            while (block.getFirstInstruction() != null) {
+                Instruction instruction = block.getFirstInstruction();
+                instruction.delete();
+                splitBlock.add(instruction);
+            }
         }
 
         return splitBlock;

core/src/main/java/org/teavm/runtime/EventQueue.java

@@ -0,0 +1,147 @@
+/*
+ *  Copyright 2018 Alexey Andreev.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.teavm.runtime;
+
+import java.util.Arrays;
+import org.teavm.interop.Import;
+import org.teavm.interop.StaticInit;
+
+@StaticInit
+public final class EventQueue {
+    private static Node[] data = new Node[16];
+    private static int size;
+    private static boolean finished;
+    private static int idGenerator;
+
+    private EventQueue() {
+    }
+
+    public static int offer(Event action) {
+        return offer(action, System.currentTimeMillis());
+    }
+
+    public static int offer(Event action, long time) {
+        ensureCapacity(size + 1);
+        int current = size;
+        while (current > 0) {
+            int parent = (current - 1) / 2;
+            if (time < data[parent].time) {
+                data[current] = data[parent];
+                current = parent;
+            } else {
+                break;
+            }
+        }
+        int id = idGenerator++;
+        data[current] = new Node(id, action, time);
+        ++size;
+        if (current == 0) {
+            interrupt();
+        }
+        return id;
+    }
+
+    public static void kill(int id) {
+        for (int i = 0; i < data.length; ++i) {
+            if (data[i].id == id) {
+                remove(i);
+                break;
+            }
+        }
+    }
+
+    public static void process() {
+        while (!finished) {
+            next();
+        }
+    }
+
+    static void stop() {
+        finished = true;
+    }
+
+    private static void next() {
+        while (data.length == 0) {
+            waitUntil(System.currentTimeMillis() + 1000);
+        }
+        Node node = data[0];
+        waitUntil(node.time);
+        if (node.time <= System.currentTimeMillis()) {
+            remove(0);
+            node.event.run();
+        }
+    }
+
+    private static void remove(int index) {
+        Node item = data[size - 1];
+        while (true) {
+            int left = index * 2 + 1;
+            int right = left + 1;
+            int next;
+            if (left >= size) {
+                break;
+            } else if (right >= size || data[left].time < data[right].time) {
+                next = left;
+            } else {
+                next = right;
+            }
+            if (item.time <= data[next].time) {
+                break;
+            }
+            data[index] = data[next];
+            index = next;
+        }
+        data[index] = item;
+    }
+
+    private static void waitUntil(long time) {
+        long diff = time - System.currentTimeMillis();
+        if (diff <= 0) {
+            return;
+        }
+        waitFor(diff);
+    }
+
+    @Import(name = "teavm_waitFor")
+    private static native void waitFor(long time);
+
+    @Import(name = "teavm_interrupt")
+    private static native void interrupt();
+
+    private static void ensureCapacity(int capacity) {
+        if (data.length >= capacity) {
+            return;
+        }
+        capacity = Math.max(capacity, data.length * 3 / 2);
+        data = Arrays.copyOf(data, capacity);
+    }
+
+    static class Node {
+        final int id;
+        final Event event;
+        final long time;
+
+        Node(int id, Event event, long time) {
+            this.id = id;
+            this.event = event;
+            this.time = time;
+        }
+    }
+
+    public interface Event {
+        void run();
+    }
+}

core/src/main/java/org/teavm/runtime/Fiber.java

@@ -0,0 +1,243 @@
+/*
+ *  Copyright 2018 Alexey Andreev.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.teavm.runtime;
+
+import java.util.Arrays;
+import org.teavm.interop.AsyncCallback;
+import org.teavm.interop.StaticInit;
+import org.teavm.interop.Unmanaged;
+
+@StaticInit
+public class Fiber {
+    public static final int STATE_RUNNING = 0;
+    public static final int STATE_SUSPENDING = 1;
+    public static final int STATE_RESUMING = 2;
+
+    private int[] intValues;
+    private int intTop;
+    private long[] longValues;
+    private int longTop;
+    private float[] floatValues;
+    private int floatTop;
+    private double[] doubleValues;
+    private int doubleTop;
+    private Object[] objectValues;
+    private int objectTop;
+    private int state;
+    private FiberRunner runner;
+    private Object result;
+    private Throwable exception;
+
+    private static Fiber current;
+
+    private Fiber(FiberRunner runner) {
+        this.runner = runner;
+    }
+
+    public void push(int value) {
+        if (intValues == null) {
+            intValues = new int[4];
+        } else if (intTop + 1 == intValues.length) {
+            intValues = Arrays.copyOf(intValues, intValues.length * 3 / 2);
+        }
+        intValues[intTop++] = value;
+    }
+
+    public void push(long value) {
+        if (longValues == null) {
+            longValues = new long[4];
+        } else if (longTop + 1 == longValues.length) {
+            longValues = Arrays.copyOf(longValues, longValues.length * 3 / 2);
+        }
+        longValues[longTop++] = value;
+    }
+
+    public void push(float value) {
+        if (floatValues == null) {
+            floatValues = new float[4];
+        } else if (floatTop + 1 == floatValues.length) {
+            floatValues = Arrays.copyOf(floatValues, floatValues.length * 3 / 2);
+        }
+        floatValues[floatTop++] = value;
+    }
+
+    public void push(double value) {
+        if (doubleValues == null) {
+            doubleValues = new double[4];
+        } else if (doubleTop + 4 == doubleValues.length) {
+            doubleValues = Arrays.copyOf(doubleValues, doubleValues.length * 3 / 2);
+        }
+        doubleValues[doubleTop++] = value;
+    }
+
+    public void push(Object value) {
+        if (objectValues == null) {
+            objectValues = new Object[4];
+        } else if (objectTop + 4 == objectValues.length) {
+            objectValues = Arrays.copyOf(objectValues, objectValues.length * 3 / 2);
+        }
+        objectValues[objectTop++] = value;
+    }
+
+    @Unmanaged
+    public int popInt() {
+        return intValues[--intTop];
+    }
+
+    @Unmanaged
+    public long popLong() {
+        return longValues[--longTop];
+    }
+
+    @Unmanaged
+    public float popFloat() {
+        return floatValues[--floatTop];
+    }
+
+    @Unmanaged
+    public double popDouble() {
+        return doubleValues[--doubleTop];
+    }
+
+    @Unmanaged
+    public Object popObject() {
+        Object result = objectValues[--objectTop];
+        objectValues[objectTop] = null;
+        return result;
+    }
+
+    @Unmanaged
+    public static Fiber current() {
+        return current;
+    }
+
+    @Unmanaged
+    public boolean isSuspending() {
+        return state == STATE_SUSPENDING;
+    }
+
+    @Unmanaged
+    public boolean isResuming() {
+        return state == STATE_RESUMING;
+    }
+
+    @Unmanaged
+    public static boolean getBoolean(Object v) {
+        return v != null ? (Boolean) v : false;
+    }
+
+    @Unmanaged
+    public static byte getByte(Object v) {
+        return v != null ? (Byte) v : 0;
+    }
+
+    @Unmanaged
+    public static short getShort(Object v) {
+        return v != null ? (Short) v : 0;
+    }
+
+    @Unmanaged
+    public static int getInt(Object v) {
+        return v != null ? (Integer) v : 0;
+    }
+
+    @Unmanaged
+    public static char getChar(Object v) {
+        return v != null ? (Character) v : 0;
+    }
+
+    @Unmanaged
+    public static long getLong(Object v) {
+        return v != null ? (Long) v : 0;
+    }
+
+    @Unmanaged
+    public static float getFloat(Object v) {
+        return v != null ? (Float) v : 0;
+    }
+
+    @Unmanaged
+    public static double getDouble(Object v) {
+        return v != null ? (Double) v : 0;
+    }
+
+    public static Object suspend(AsyncCall call) throws Throwable {
+        Fiber fiber = current();
+        Thread javaThread = Thread.currentThread();
+        if (fiber.isResuming()) {
+            fiber.state = STATE_RUNNING;
+            if (fiber.exception != null) {
+                throw fiber.exception;
+            }
+            return fiber.result;
+        }
+
+        fiber.state = STATE_SUSPENDING;
+        call.run(new AsyncCallback<Object>() {
+            @Override
+            public void complete(Object result) {
+                setCurrentThread(javaThread);
+                fiber.result = result;
+                fiber.resume();
+            }
+
+            @Override
+            public void error(Throwable e) {
+                setCurrentThread(javaThread);
+                fiber.exception = e;
+                fiber.resume();
+            }
+        });
+        return null;
+    }
+
+    static native void setCurrentThread(Thread thread);
+
+    public static void start(FiberRunner runner) {
+        new Fiber(runner).start();
+    }
+
+    static void startMain() {
+        start(() -> {
+            runMain();
+            if (!current().isSuspending()) {
+                EventQueue.stop();
+            }
+        });
+    }
+
+    static native void runMain();
+
+    private void start() {
+        Fiber former = current;
+        current = this;
+        runner.run();
+        current = former;
+    }
+
+    private void resume() {
+        state = STATE_RESUMING;
+        start();
+    }
+
+    public interface FiberRunner {
+        void run();
+    }
+
+    public interface AsyncCall {
+        void run(AsyncCallback<?> callback);
+    }
+}

core/src/main/java/org/teavm/vm/TeaVM.java

@@ -24,6 +24,7 @@ import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.LinkedHashMap;
+import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Properties;
@@ -377,6 +378,10 @@ public class TeaVM implements TeaVMHost, ServiceRepository {
             return;
         }
 
+        target.analyzeBeforeOptimizations(new ListableClassReaderSourceAdapter(
+                dependencyAnalyzer.getClassSource(),
+                new LinkedHashSet<>(dependencyAnalyzer.getReachableClasses())));
+
         boolean isLazy = optimizationLevel == TeaVMOptimizationLevel.SIMPLE;
         ListableClassHolderSource classSet;
         if (isLazy) {
@@ -869,4 +874,24 @@ public class TeaVM implements TeaVMHost, ServiceRepository {
             return classNames;
         }
     }
+
+    static class ListableClassReaderSourceAdapter implements ListableClassReaderSource {
+        private ClassReaderSource classSource;
+        private Set<String> classes;
+
+        ListableClassReaderSourceAdapter(ClassReaderSource classSource, Set<String> classes) {
+            this.classSource = classSource;
+            this.classes = Collections.unmodifiableSet(classes);
+        }
+
+        @Override
+        public Set<String> getClassNames() {
+            return classes;
+        }
+
+        @Override
+        public ClassReader get(String name) {
+            return classes.contains(name) ? classSource.get(name) : null;
+        }
+    }
 }

core/src/main/java/org/teavm/vm/TeaVMTarget.java

@@ -21,6 +21,7 @@ import org.teavm.dependency.DependencyAnalyzer;
 import org.teavm.dependency.DependencyListener;
 import org.teavm.model.ClassHolderTransformer;
 import org.teavm.model.ListableClassHolderSource;
+import org.teavm.model.ListableClassReaderSource;
 import org.teavm.model.MethodReader;
 import org.teavm.model.Program;
 import org.teavm.vm.spi.TeaVMHostExtension;
@@ -38,6 +39,9 @@ public interface TeaVMTarget {
 
     void contributeDependencies(DependencyAnalyzer dependencyAnalyzer);
 
+    default void analyzeBeforeOptimizations(ListableClassReaderSource classSource) {
+    }
+
     void beforeOptimizations(Program program, MethodReader method);
 
     void afterOptimizations(Program program, MethodReader method);

core/src/main/resources/org/teavm/backend/c/runtime.c

@@ -13,6 +13,7 @@
 #include <stdalign.h>
 #include <unistd.h>
 #include <sys/mman.h>
+#include <signal.h>
 #endif
 
 #ifdef _MSC_VER
@@ -29,6 +30,8 @@ typedef struct JavaArray JavaArray;
 typedef struct JavaClass JavaClass;
 typedef struct JavaString JavaString;
 
+static void* gc_heapAddress = NULL;
+
 #define PACK_CLASS(cls) ((int32_t) ((uintptr_t) ((char*) (cls) - TeaVM_beforeClasses) >> 3))
 #define UNPACK_CLASS(cls) ((JavaClass*) (TeaVM_beforeClasses + ((cls) << 3)))
 #define CLASS_OF(obj) (UNPACK_CLASS(((JavaObject*) (obj))->header))
@@ -42,6 +45,11 @@ typedef struct JavaString JavaString;
 #define TO_SHORT(i) ((((i) << 16) >> 16))
 #define TO_CHAR(i) ((char16_t) (i))
 
+#define PACK_MONITOR(ref) (((int32_t) ((uintptr_t) (ref) - (uintptr_t) gc_heapAddress) / sizeof(int)) | 0x80000000)
+#define UNPACK_MONITOR(ref) ((ref & 0x80000000) != 0 \
+  ? (void*) (((uintptr_t) ((ref & 0x7FFFFFFF) * sizeof(int)) + (uintptr_t) gc_heapAddress)) \
+  : NULL)
+
 static inline int32_t compare_i32(int32_t a, int32_t b) {
     return a > b ? INT32_C(1) : a < b ? INT32_C(-1) : INT32_C(0);
 }
@@ -100,7 +108,6 @@ static void** stackTop;
 
 static void* gc_gcStorageAddress = NULL;
 static int32_t gc_gcStorageSize = INT32_C(0);
-static void* gc_heapAddress = NULL;
 static void* gc_regionsAddress = NULL;
 static int32_t gc_regionSize = INT32_C(32768);
 static int32_t gc_regionMaxCount = INT32_C(0);
@@ -156,8 +163,31 @@ static inline void* teavm_lookupResourceValue(TeaVM_ResourceMap *map, JavaString
 
 static JavaArray* teavm_resourceMapKeys(TeaVM_ResourceMap *);
 
+
+#ifdef __GNUC__
+static timer_t teavm_queueTimer;
+#endif
+
 static void TeaVM_beforeInit() {
     srand(time(NULL));
+
+    #ifdef __GNUC__
+    struct sigaction sigact;
+    sigact.sa_flags = 0;
+    sigact.sa_handler = NULL;
+    sigaction(SIGRTMIN, &sigact, NULL);
+
+    sigset_t signals;
+    sigemptyset(&signals );
+    sigaddset(&signals, SIGRTMIN);
+    sigprocmask(SIG_BLOCK, &signals, NULL);
+
+    struct sigevent sev;
+    sev.sigev_notify = SIGEV_SIGNAL;
+    sev.sigev_signo = SIGRTMIN;
+    timer_create(CLOCK_REALTIME, &sev, &teavm_queueTimer);
+
+    #endif
 }
 
 #ifdef __GNUC__
@@ -295,3 +325,26 @@ static inline float teavm_reinterpretIntToFloat(int32_t v) {
     conv.intValue = v;
     return conv.floatValue;
 }
+
+#ifdef __GNUC__
+
+static void teavm_waitFor(int64_t timeout) {
+    struct itimerspec its = {0};
+    its.it_value.tv_sec = timeout / 1000;
+    its.it_value.tv_nsec = (timeout % 1000) * 1000000L;
+    timer_settime(teavm_queueTimer, 0, &its, NULL);
+
+    sigset_t signals;
+    sigemptyset(&signals);
+    sigaddset(&signals, SIGRTMIN);
+    siginfo_t actualSignal;
+    sigwaitinfo(&signals, &actualSignal);
+}
+
+static void teavm_interrupt() {
+    struct itimerspec its = {0};
+    timer_settime(teavm_queueTimer, 0, &its, NULL);
+    raise(SIGRTMIN);
+}
+
+#endif

interop/core/src/main/java/org/teavm/interop/AsyncCallback.java

@@ -1,5 +1,5 @@
 /*
- *  Copyright 2015 Alexey Andreev.
+ *  Copyright 2018 Alexey Andreev.
  *
  *  Licensed under the Apache License, Version 2.0 (the "License");
  *  you may not use this file except in compliance with the License.
@@ -13,13 +13,8 @@
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  */
-package org.teavm.platform.async;
+package org.teavm.interop;
 
-/**
- *
- * @author Alexey Andreev
- * @param <T>
- */
 public interface AsyncCallback<T> {
     void complete(T result);
 

platform/src/main/java/org/teavm/platform/LowLevelQueue.java

@@ -0,0 +1,47 @@
+/*
+ *  Copyright 2019 konsoletyper.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.teavm.platform;
+
+import java.util.ArrayDeque;
+import java.util.Queue;
+
+public class LowLevelQueue<T> extends PlatformQueue<T> {
+    Queue<T> q = new ArrayDeque<>();
+
+    @Override
+    public int getLength() {
+        return q.size();
+    }
+
+    @Override
+    void push(PlatformObject obj) {
+    }
+
+    @Override
+    PlatformObject shift() {
+        return null;
+    }
+
+    @Override
+    public void add(T e) {
+        q.add(e);
+    }
+
+    @Override
+    public T remove() {
+        return q.remove();
+    }
+}

platform/src/main/java/org/teavm/platform/Platform.java

@@ -21,6 +21,8 @@ import org.teavm.backend.javascript.spi.InjectedBy;
 import org.teavm.dependency.PluggableDependency;
 import org.teavm.interop.Address;
 import org.teavm.interop.DelegateTo;
+import org.teavm.interop.PlatformMarker;
+import org.teavm.interop.PlatformMarkers;
 import org.teavm.interop.Unmanaged;
 import org.teavm.jso.JSBody;
 import org.teavm.jso.JSObject;
@@ -193,7 +195,16 @@ public final class Platform {
     }
 
     @JSBody(script = "return [];")
-    public static native <T> PlatformQueue<T> createQueue();
+    public static <T> PlatformQueue<T> createQueue() {
+        if (isLowLevel()) {
+            return new LowLevelQueue<>();
+        } else {
+            return createQueueJs();
+        }
+    }
+
+    @JSBody(script = "return [];")
+    private static native  <T> PlatformQueue<T> createQueueJs();
 
     public static PlatformString stringFromCharCode(int charCode) {
         return JSString.fromCharCode(charCode).cast();
@@ -230,4 +241,9 @@ public final class Platform {
     public static String getName(PlatformClass cls) {
         return cls.getMetadata().getName();
     }
+
+    @PlatformMarker(PlatformMarkers.LOW_LEVEL)
+    private static boolean isLowLevel() {
+        return false;
+    }
 }

platform/src/main/java/org/teavm/platform/PlatformQueue.java

@@ -33,11 +33,11 @@ public abstract class PlatformQueue<T> implements JSObject {
 
     abstract PlatformObject shift();
 
-    public final void add(T e) {
+    public void add(T e) {
         push(wrap(e));
     }
 
-    public final T remove() {
+    public T remove() {
         return unwrap(shift());
     }
 

platform/src/main/java/org/teavm/platform/plugin/AsyncCallClass.java

@@ -0,0 +1,20 @@
+/*
+ *  Copyright 2018 Alexey Andreev.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.teavm.platform.plugin;
+
+@interface AsyncCallClass {
+    String value();
+}

platform/src/main/java/org/teavm/platform/plugin/AsyncCallbackWrapper.java

@@ -15,7 +15,7 @@
  */
 package org.teavm.platform.plugin;
 
-import org.teavm.platform.async.AsyncCallback;
+import org.teavm.interop.AsyncCallback;
 
 class AsyncCallbackWrapper<T> implements AsyncCallback<T> {
     private AsyncCallback<T> realAsyncCallback;

platform/src/main/java/org/teavm/platform/plugin/AsyncLowLevelDependencyListener.java

@@ -0,0 +1,230 @@
+/*
+ *  Copyright 2018 Alexey Andreev.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.teavm.platform.plugin;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+import org.teavm.dependency.AbstractDependencyListener;
+import org.teavm.dependency.DependencyAgent;
+import org.teavm.dependency.MethodDependency;
+import org.teavm.interop.Async;
+import org.teavm.interop.AsyncCallback;
+import org.teavm.model.AnnotationReader;
+import org.teavm.model.BasicBlock;
+import org.teavm.model.ClassHolder;
+import org.teavm.model.ElementModifier;
+import org.teavm.model.FieldHolder;
+import org.teavm.model.FieldReference;
+import org.teavm.model.MethodHolder;
+import org.teavm.model.MethodReader;
+import org.teavm.model.MethodReference;
+import org.teavm.model.Program;
+import org.teavm.model.ValueType;
+import org.teavm.model.Variable;
+import org.teavm.model.instructions.ExitInstruction;
+import org.teavm.model.instructions.GetFieldInstruction;
+import org.teavm.model.instructions.InvocationType;
+import org.teavm.model.instructions.InvokeInstruction;
+import org.teavm.model.instructions.PutFieldInstruction;
+import org.teavm.runtime.Fiber;
+
+public class AsyncLowLevelDependencyListener extends AbstractDependencyListener {
+    private Set<String> generatedClassNames = new HashSet<>();
+
+    @Override
+    public void methodReached(DependencyAgent agent, MethodDependency method) {
+        if (method.getMethod() != null && method.getMethod().getAnnotations().get(Async.class.getName()) != null) {
+            ClassHolder cls = generateCall(method.getMethod());
+            if (cls != null) {
+                agent.submitClass(cls);
+            }
+        }
+    }
+
+    private ClassHolder generateCall(MethodReader method) {
+        ClassHolder cls = generateClassDecl(method);
+        if (cls == null) {
+            return null;
+        }
+        cls.addMethod(generateConstructor(method, cls.getName()));
+        cls.addMethod(generateRun(method, cls.getName()));
+        return cls;
+    }
+
+    private ClassHolder generateClassDecl(MethodReader method) {
+        AnnotationReader annot = method.getAnnotations().get(AsyncCallClass.class.getName());
+        String className = annot.getValue("value").getString();
+        if (!generatedClassNames.add(className)) {
+            return null;
+        }
+        ClassHolder cls = new ClassHolder(className);
+
+        cls.getInterfaces().add(Fiber.class.getName() + "$AsyncCall");
+
+        List<ValueType> types = new ArrayList<>();
+        if (!method.hasModifier(ElementModifier.STATIC)) {
+            types.add(ValueType.object(method.getOwnerName()));
+            FieldHolder field = new FieldHolder("instance");
+            field.setType(ValueType.object(method.getOwnerName()));
+            cls.addField(field);
+        }
+        ValueType[] parameterTypes = method.getParameterTypes();
+        for (int i = 0; i < parameterTypes.length; ++i) {
+            types.add(parameterTypes[i]);
+            FieldHolder field = new FieldHolder("param" + i);
+            field.setType(parameterTypes[i]);
+            cls.addField(field);
+        }
+        types.add(ValueType.VOID);
+        MethodHolder constructor = new MethodHolder("<init>", types.toArray(new ValueType[0]));
+        cls.addMethod(constructor);
+        return cls;
+    }
+
+    private MethodHolder generateConstructor(MethodReader method, String className) {
+        List<ValueType> types = new ArrayList<>();
+        if (!method.hasModifier(ElementModifier.STATIC)) {
+            types.add(ValueType.object(method.getOwnerName()));
+        }
+        Collections.addAll(types, method.getParameterTypes());
+        types.add(ValueType.VOID);
+        MethodHolder constructor = new MethodHolder("<init>", types.toArray(new ValueType[0]));
+
+        Program program = new Program();
+        constructor.setProgram(program);
+        BasicBlock block = program.createBasicBlock();
+        Variable instance = program.createVariable();
+
+        if (!method.hasModifier(ElementModifier.STATIC)) {
+            PutFieldInstruction putField = new PutFieldInstruction();
+            putField.setValue(program.createVariable());
+            putField.setField(new FieldReference(className, "instance"));
+            putField.setFieldType(ValueType.object(method.getOwnerName()));
+            putField.setInstance(instance);
+            block.add(putField);
+        }
+
+        for (int i = 0; i < method.parameterCount(); ++i) {
+            PutFieldInstruction putField = new PutFieldInstruction();
+            putField.setValue(program.createVariable());
+            putField.setField(new FieldReference(className, "param" + i));
+            putField.setFieldType(method.parameterType(i));
+            putField.setInstance(instance);
+            block.add(putField);
+        }
+
+        block.add(new ExitInstruction());
+        return constructor;
+    }
+
+    private MethodHolder generateRun(MethodReader method, String className) {
+        MethodHolder runMethod = new MethodHolder("run", ValueType.parse(AsyncCallback.class), ValueType.VOID);
+        Program program = new Program();
+        runMethod.setProgram(program);
+        BasicBlock block = program.createBasicBlock();
+        Variable instance = program.createVariable();
+        Variable callback = program.createVariable();
+
+        InvokeInstruction call = new InvokeInstruction();
+        call.setType(InvocationType.SPECIAL);
+        List<ValueType> types = new ArrayList<>();
+        ValueType[] parameterTypes = method.getParameterTypes();
+        List<Variable> arguments = new ArrayList<>(call.getArguments());
+
+        if (!method.hasModifier(ElementModifier.STATIC)) {
+            GetFieldInstruction getField = new GetFieldInstruction();
+            getField.setReceiver(program.createVariable());
+            getField.setInstance(instance);
+            getField.setField(new FieldReference(className, "instance"));
+            getField.setFieldType(ValueType.object(method.getOwnerName()));
+            block.add(getField);
+            call.setInstance(getField.getReceiver());
+        }
+        for (int i = 0; i < parameterTypes.length; ++i) {
+            GetFieldInstruction getField = new GetFieldInstruction();
+            getField.setReceiver(program.createVariable());
+            getField.setInstance(instance);
+            getField.setField(new FieldReference(className, "param" + i));
+            getField.setFieldType(parameterTypes[i]);
+            block.add(getField);
+            arguments.add(getField.getReceiver());
+            types.add(parameterTypes[i]);
+        }
+
+        types.add(ValueType.parse(AsyncCallback.class));
+        arguments.add(callback);
+
+        types.add(ValueType.VOID);
+        call.setMethod(new MethodReference(method.getOwnerName(), method.getName(), types.toArray(new ValueType[0])));
+        call.setArguments(arguments.toArray(new Variable[0]));
+        block.add(call);
+
+        if (method.getResultType() == ValueType.VOID) {
+            block.add(new ExitInstruction());
+        } else {
+            Variable result = program.createVariable();
+            call.setReceiver(result);
+            ExitInstruction exit = new ExitInstruction();
+            exit.setValueToReturn(castToObject(block, result, method.getResultType()));
+            block.add(exit);
+        }
+
+        return runMethod;
+    }
+
+    private Variable castToObject(BasicBlock block, Variable value, ValueType type) {
+        if (type instanceof ValueType.Primitive) {
+            InvokeInstruction invoke = new InvokeInstruction();
+            invoke.setType(InvocationType.SPECIAL);
+            invoke.setArguments(value);
+            invoke.setReceiver(block.getProgram().createVariable());
+            switch (((ValueType.Primitive) type).getKind()) {
+                case BOOLEAN:
+                    invoke.setMethod(new MethodReference(Boolean.class, "valueOf", boolean.class, Boolean.class));
+                    break;
+                case BYTE:
+                    invoke.setMethod(new MethodReference(Byte.class, "valueOf", byte.class, Byte.class));
+                    break;
+                case SHORT:
+                    invoke.setMethod(new MethodReference(Short.class, "valueOf", short.class, Short.class));
+                    break;
+                case CHARACTER:
+                    invoke.setMethod(new MethodReference(Character.class, "valueOf", char.class, Character.class));
+                    break;
+                case INTEGER:
+                    invoke.setMethod(new MethodReference(Integer.class, "valueOf", int.class, Integer.class));
+                    break;
+                case LONG:
+                    invoke.setMethod(new MethodReference(Long.class, "valueOf", long.class, Long.class));
+                    break;
+                case FLOAT:
+                    invoke.setMethod(new MethodReference(Float.class, "valueOf", float.class, Float.class));
+                    break;
+                case DOUBLE:
+                    invoke.setMethod(new MethodReference(Double.class, "valueOf", double.class, Double.class));
+                    break;
+            }
+
+            block.add(invoke);
+            return invoke.getReceiver();
+        }
+
+        return value;
+    }
+}

platform/src/main/java/org/teavm/platform/plugin/AsyncMethodGenerator.java

@@ -24,13 +24,13 @@ import org.teavm.backend.javascript.spi.VirtualMethodContributorContext;
 import org.teavm.dependency.DependencyAgent;
 import org.teavm.dependency.DependencyPlugin;
 import org.teavm.dependency.MethodDependency;
+import org.teavm.interop.AsyncCallback;
 import org.teavm.model.ClassReader;
 import org.teavm.model.ElementModifier;
 import org.teavm.model.MethodDescriptor;
 import org.teavm.model.MethodReader;
 import org.teavm.model.MethodReference;
 import org.teavm.model.ValueType;
-import org.teavm.platform.async.AsyncCallback;
 
 public class AsyncMethodGenerator implements Generator, DependencyPlugin, VirtualMethodContributor {
     private static final MethodDescriptor completeMethod = new MethodDescriptor("complete", Object.class, void.class);

platform/src/main/java/org/teavm/platform/plugin/AsyncMethodProcessor.java

@@ -15,8 +15,14 @@
  */
 package org.teavm.platform.plugin;
 
+import java.util.ArrayList;
+import java.util.List;
 import org.teavm.backend.javascript.spi.GeneratedBy;
 import org.teavm.interop.Async;
+import org.teavm.interop.AsyncCallback;
+import org.teavm.model.AnnotationHolder;
+import org.teavm.model.AnnotationValue;
+import org.teavm.model.BasicBlock;
 import org.teavm.model.CallLocation;
 import org.teavm.model.ClassHolder;
 import org.teavm.model.ClassHolderTransformer;
@@ -24,12 +30,27 @@ import org.teavm.model.ClassHolderTransformerContext;
 import org.teavm.model.ElementModifier;
 import org.teavm.model.MethodDescriptor;
 import org.teavm.model.MethodHolder;
+import org.teavm.model.MethodReference;
+import org.teavm.model.Program;
 import org.teavm.model.ValueType;
-import org.teavm.platform.async.AsyncCallback;
+import org.teavm.model.Variable;
+import org.teavm.model.instructions.CastInstruction;
+import org.teavm.model.instructions.ConstructInstruction;
+import org.teavm.model.instructions.ExitInstruction;
+import org.teavm.model.instructions.InvocationType;
+import org.teavm.model.instructions.InvokeInstruction;
+import org.teavm.runtime.Fiber;
 
 public class AsyncMethodProcessor implements ClassHolderTransformer {
+    private boolean lowLevel;
+
+    public AsyncMethodProcessor(boolean lowLevel) {
+        this.lowLevel = lowLevel;
+    }
+
     @Override
     public void transformClass(ClassHolder cls, ClassHolderTransformerContext context) {
+        int suffix = 0;
         for (MethodHolder method : cls.getMethods()) {
             if (method.hasModifier(ElementModifier.NATIVE)
                     && method.getAnnotations().get(Async.class.getName()) != null
@@ -50,7 +71,112 @@ public class AsyncMethodProcessor implements ClassHolderTransformer {
                                 method.getReference(), asyncMethod.getReference());
                     }
                 }
+
+                if (lowLevel) {
+                    generateLowLevelCall(method, suffix++);
+                }
             }
         }
     }
+
+    private void generateLowLevelCall(MethodHolder method, int suffix) {
+        String className = method.getOwnerName() + "$" + method.getName() + "$" + suffix;
+        AnnotationHolder classNameAnnot = new AnnotationHolder(AsyncCallClass.class.getName());
+        classNameAnnot.getValues().put("value", new AnnotationValue(className));
+        method.getAnnotations().add(classNameAnnot);
+
+        method.getModifiers().remove(ElementModifier.NATIVE);
+
+        Program program = new Program();
+        method.setProgram(program);
+        BasicBlock block = program.createBasicBlock();
+
+        InvokeInstruction constructorInvocation = new InvokeInstruction();
+        constructorInvocation.setType(InvocationType.SPECIAL);
+        List<ValueType> signature = new ArrayList<>();
+
+        Variable instanceVar = program.createVariable();
+        List<Variable> arguments = new ArrayList<>(constructorInvocation.getArguments());
+        if (!method.hasModifier(ElementModifier.STATIC)) {
+            arguments.add(instanceVar);
+            signature.add(ValueType.object(method.getOwnerName()));
+        }
+        for (int i = 0; i < method.parameterCount(); ++i) {
+            arguments.add(program.createVariable());
+            signature.add(method.parameterType(i));
+        }
+        signature.add(ValueType.VOID);
+
+        ConstructInstruction newInstruction = new ConstructInstruction();
+        newInstruction.setReceiver(program.createVariable());
+        newInstruction.setType(className);
+        block.add(newInstruction);
+
+        constructorInvocation.setInstance(newInstruction.getReceiver());
+        constructorInvocation.setMethod(new MethodReference(className, "<init>", signature.toArray(new ValueType[0])));
+        constructorInvocation.setArguments(arguments.toArray(new Variable[0]));
+        block.add(constructorInvocation);
+
+        InvokeInstruction suspendInvocation = new InvokeInstruction();
+        suspendInvocation.setType(InvocationType.SPECIAL);
+        suspendInvocation.setMethod(new MethodReference(Fiber.class, "suspend", Fiber.AsyncCall.class, Object.class));
+        suspendInvocation.setArguments(newInstruction.getReceiver());
+        suspendInvocation.setReceiver(program.createVariable());
+        block.add(suspendInvocation);
+
+        Variable result = suspendInvocation.getReceiver();
+        ExitInstruction exitInstruction = new ExitInstruction();
+        ValueType returnType = method.getResultType();
+        if (returnType instanceof ValueType.Primitive) {
+            switch (((ValueType.Primitive) returnType).getKind()) {
+                case BOOLEAN:
+                    result = castPrimitive(block, result, "Boolean", returnType);
+                    break;
+                case BYTE:
+                    result = castPrimitive(block, result, "Byte", returnType);
+                    break;
+                case SHORT:
+                    result = castPrimitive(block, result, "Short", returnType);
+                    break;
+                case CHARACTER:
+                    result = castPrimitive(block, result, "Char", returnType);
+                    break;
+                case INTEGER:
+                    result = castPrimitive(block, result, "Int", returnType);
+                    break;
+                case FLOAT:
+                    result = castPrimitive(block, result, "Float", returnType);
+                    break;
+                case LONG:
+                    result = castPrimitive(block, result, "Long", returnType);
+                    break;
+                case DOUBLE:
+                    result = castPrimitive(block, result, "Double", returnType);
+                    break;
+            }
+        } else if (returnType == ValueType.VOID) {
+            result = null;
+        } else {
+            CastInstruction cast = new CastInstruction();
+            cast.setValue(result);
+            cast.setTargetType(returnType);
+            cast.setReceiver(program.createVariable());
+            block.add(cast);
+            result = cast.getReceiver();
+        }
+
+        exitInstruction.setValueToReturn(result);
+        block.add(exitInstruction);
+    }
+
+    private Variable castPrimitive(BasicBlock block, Variable value, String name, ValueType type) {
+        InvokeInstruction invoke = new InvokeInstruction();
+        invoke.setType(InvocationType.SPECIAL);
+        invoke.setMethod(new MethodReference(Fiber.class.getName(), "get" + name,
+                ValueType.object("java.lang.Object"), type));
+        invoke.setArguments(value);
+        invoke.setReceiver(block.getProgram().createVariable());
+        block.add(invoke);
+        return invoke.getReceiver();
+    }
 }

platform/src/main/java/org/teavm/platform/plugin/PlatformPlugin.java

@@ -56,6 +56,7 @@ public class PlatformPlugin implements TeaVMPlugin {
                 return method.getAnnotations().get(Async.class.getName()) != null
                         ? new AsyncMethodGenerator() : null;
             });
+            host.add(new AsyncDependencyListener());
             jsHost.addVirtualMethods(new AsyncMethodGenerator());
         } else if (!isBootstrap()) {
             host.add(new StringAmplifierTransformer());
@@ -101,12 +102,15 @@ public class PlatformPlugin implements TeaVMPlugin {
             }
         }
 
-        host.add(new AsyncMethodProcessor());
+        host.add(new AsyncMethodProcessor(host.getExtension(TeaVMJavaScriptHost.class) == null));
         host.add(new NewInstanceDependencySupport());
         host.add(new ClassLookupDependencySupport());
         host.add(new EnumDependencySupport());
         host.add(new PlatformDependencyListener());
-        host.add(new AsyncDependencyListener());
+
+        if (host.getExtension(TeaVMJavaScriptHost.class) == null) {
+            host.add(new AsyncLowLevelDependencyListener());
+        }
 
         TeaVMPluginUtil.handleNatives(host, Platform.class);
         TeaVMPluginUtil.handleNatives(host, PlatformQueue.class);

tests/src/test/java/org/teavm/vm/VMTest.java

@@ -23,10 +23,10 @@ import java.util.function.Supplier;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.teavm.interop.Async;
+import org.teavm.interop.AsyncCallback;
 import org.teavm.jso.JSBody;
 import org.teavm.junit.SkipJVM;
 import org.teavm.junit.TeaVMTestRunner;
-import org.teavm.platform.async.AsyncCallback;
 
 @RunWith(TeaVMTestRunner.class)
 public class VMTest {