WASM: add some GC interop methods

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

@@ -15,6 +15,9 @@
  */
 package org.teavm.classlib.java.lang;
 
+import org.teavm.interop.DelegateTo;
+import org.teavm.runtime.GC;
+
 /**
  * A dummy class for compatibility.  Currently these methods don't actually
  * do anything.
@@ -35,10 +38,15 @@ public class TRuntime {
      * Returns the amount of free memory in the system. Calling the gc method
      * may result in increasing the value returned by freeMemory.
      */
+    @DelegateTo("freeMemoryLowLevel")
     public long freeMemory() {
         return Integer.MAX_VALUE;
     }
 
+    private long freeMemoryLowLevel() {
+        return GC.getFreeMemory();
+    }
+
     /**
      * Runs the garbage collector. Calling this method suggests that the Java
      * Virtual Machine expend effort toward recycling unused objects in order to
@@ -51,6 +59,7 @@ public class TRuntime {
      * means of invoking this method.
      */
     public void gc() {
+        System.gc();
     }
 
     /**
@@ -68,7 +77,12 @@ public class TRuntime {
      * environment. Note that the amount of memory required to hold an object of
      * any given type may be implementation-dependent.
      */
+    @DelegateTo("totalMemoryLowLevel")
     public long totalMemory() {
         return Integer.MAX_VALUE;
     }
+
+    private long totalMemoryLowLevel() {
+        return GC.availableBytes();
+    }
 }

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

@@ -26,6 +26,7 @@ import org.teavm.interop.DelegateTo;
 import org.teavm.interop.Import;
 import org.teavm.interop.Unmanaged;
 import org.teavm.runtime.Allocator;
+import org.teavm.runtime.GC;
 import org.teavm.runtime.RuntimeArray;
 import org.teavm.runtime.RuntimeClass;
 
@@ -126,10 +127,15 @@ public final class TSystem extends TObject {
     @PluggableDependency(SystemNativeGenerator.class)
     public static native void setOut(TPrintStream err);
 
+    @DelegateTo("gcLowLevel")
     public static void gc() {
         // Do nothing
     }
 
+    private static void gcLowLevel() {
+        GC.collectGarbage(0);
+    }
+
     public static void runFinalization() {
         // Do nothing
     }

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

@@ -30,6 +30,7 @@ public final class GC {
     static FreeChunk currentChunk;
     static FreeChunkHolder currentChunkPointer;
     static int freeChunks;
+    static int freeMemory = (int) availableBytes();
 
     static native Address gcStorageAddress();
 
@@ -41,10 +42,14 @@ public final class GC {
 
     private static native int regionMaxCount();
 
-    private static native long availableBytes();
+    public static native long availableBytes();
 
     private static native int regionSize();
 
+    public static int getFreeMemory() {
+        return freeMemory;
+    }
+
     static {
         currentChunk = heapAddress().toStructure();
         currentChunk.classReference = 0;
@@ -71,6 +76,7 @@ public final class GC {
             currentChunk.classReference = 0;
             currentChunk.size = freeSize;
         }
+        freeMemory -= size;
         return current;
     }
 
@@ -93,6 +99,7 @@ public final class GC {
             if (--freeChunks == 0) {
                 return false;
             }
+            freeMemory -= currentChunk.size;
             currentChunkPointer = Structure.add(FreeChunkHolder.class, currentChunkPointer, 1);
             currentChunk = currentChunkPointer.value;
             currentChunkLimit = currentChunk.toAddress().add(currentChunk.size);
@@ -100,9 +107,10 @@ public final class GC {
         return true;
     }
 
-    private static boolean collectGarbage(int size) {
+    public static boolean collectGarbage(int size) {
         mark();
         sweep();
+        updateFreeMemory();
         return true;
     }
 
@@ -268,6 +276,15 @@ public final class GC {
         currentChunkLimit = currentChunk.toAddress().add(currentChunk.size);
     }
 
+    private static void updateFreeMemory() {
+        freeMemory = 0;
+        FreeChunkHolder freeChunkPtr = currentChunkPointer;
+        for (int i = 0; i < freeChunks; ++i) {
+            freeMemory += freeChunkPtr.value.size;
+            freeChunkPtr = Structure.add(FreeChunkHolder.class, freeChunkPtr, 1);
+        }
+    }
+
     private static void sortFreeChunks(int lower, int upper) {
         int start = lower;
         int end = upper;