[Win32] Fix potential memory leak in GC#drawImage #2499

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/graphics/GC.java

@@ -16,6 +16,7 @@
 
 import java.util.*;
 import java.util.List;
+import java.util.function.*;
 import java.util.stream.*;
 
 import org.eclipse.swt.*;
@@ -494,9 +495,11 @@ public void copyArea (Image image, int x, int y) {
 private abstract class ImageOperation extends Operation {
 	private Image image;
 
+	private final Consumer<Image> disposeCallback = this::setCopyOfImage;
+
 	ImageOperation(Image image) {
 		setImage(image);
-		image.addOnDisposeListener(this::setCopyOfImage);
+		image.addOnDisposeListener(disposeCallback);
 	}
 
 	private void setImage(Image image) {
@@ -515,6 +518,11 @@ protected Image getImage() {
 		return image;
 	}
 
+	@Override
+	void disposeAll() {
+		image.removeOnDisposeListener(disposeCallback);
+		super.disposeAll();
+	}
 }
 
 private class CopyAreaToImageOperation extends ImageOperation {

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/graphics/Image.java

@@ -1020,10 +1020,18 @@ void addOnDisposeListener(Consumer<Image> onDisposeListener) {
 	onDisposeListeners.add(onDisposeListener);
 }
 
+void removeOnDisposeListener(Consumer<Image> onDisposeListener) {
+	if (onDisposeListeners == null) {
+		return;
+	}
+	onDisposeListeners.remove(onDisposeListener);
+}
+
 @Override
 public void dispose() {
 	if (onDisposeListeners != null) {
 		onDisposeListeners.forEach(listener -> listener.accept(this));
+		onDisposeListeners.clear();
 	}
 	super.dispose();
 }

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_graphics_GC.java

@@ -29,6 +29,7 @@
 import static org.junit.jupiter.api.Assumptions.assumeFalse;
 import static org.junit.jupiter.api.Assumptions.assumeTrue;
 
+import java.lang.ref.WeakReference;
 import java.util.concurrent.atomic.AtomicReference;
 
 import org.eclipse.swt.SWT;
@@ -804,6 +805,24 @@ public void test_bug1288_createGCFromImageFromNonDisplayThread() throws Interrup
 	assertNull(exceptionReference.get(), "Creating a GC from an Image without a device threw an exception");
 }
 
+// Tests that a GC instance is cleaned from memory after it was disposed.
+// Primarily supposed to test that the operations (currently only implemented for Windows) do not produce any leaks.
+@Test
+public void test_noMemoryLeakAfterDispose() {
+	GC testGC = new GC(display);
+	Image image = new Image(display, 1, 1);
+	testGC.setFont(display.getSystemFont());
+	testGC.setClipping(new Rectangle(0, 0, 2, 2));
+	testGC.drawImage(image, 0, 0);
+	testGC.drawText("Test", 0, 0);
+	testGC.drawLine(0, 0, 5, 5);
+	WeakReference<GC> testGCReference = new WeakReference<>(testGC);
+	testGC.dispose();
+	testGC = null;
+	System.gc();
+	assertNull(testGCReference.get());
+}
+
 /* custom */
 Display display;
 Shell shell;