Trigger GC in test snippet via JDI

During TestLogicalStructures, its possible that the test snippet
triggers GC before the debug framework has called Interpreter.disableCollection()
on objects created for the logical structure. In this case,
the test fails with an ObjectCollectedException.

This change adjusts how GC is performed in the test snippet of TestLogicalStructures.
Instead of waiting a fixed amount of time in the snippet and then running GC,
the tests now run GC with an evaluation, via JDI.

This ensures that Interpreter.disableCollection() is called
before GC is forced in the test snippet, avoiding potential sporadic failures.

Fixes: #301

Author: trancexpress

org.eclipse.jdt.debug.tests/java9/LogicalStructures.java

@@ -19,10 +19,8 @@
  * Tests built in logical structures.
  */
 public class LogicalStructures {
-	
+
 	public static void main(String[] args) {
-		generateGarbage();
-		
 		Map<String, Integer> map = new HashMap<>();
 		map.put("one", 1);
 		map.put("two", 2);
@@ -33,18 +31,15 @@ public static void main(String[] args) {
 		Map.Entry<String, Integer> entry = set.iterator().next();
 		entry.getKey();
 	}
-	
-	private static void generateGarbage() {
-		// generate garbage repeatedly to verify that logical values don't get GCed
-		Timer timer = new Timer(true);
-		timer.scheduleAtFixedRate(new TimerTask() {
-			private List<String> garbage;
-			@Override
-			public void run() {
-				System.gc();
-				garbage = Arrays.asList(new String("a"), new String("b"), new String("c"));
-			}
-		}, 200, 20);
+
+	// called from test to verify that logical values don't get GCed
+	private static void generateGarbageAndGC() throws InterruptedException {
+		List<Object> garbage;
+		for (int i = 0; i < 10; ++i) {
+			System.gc();
+			garbage = Arrays.asList(new Object(), new Object(), new Object());
+			Thread.sleep(20);
+		}
 	}
 
 }

org.eclipse.jdt.debug.tests/testprograms/LogicalStructures.java

@@ -19,10 +19,8 @@
  * Tests built in logical structures.
  */
 public class LogicalStructures {
-	
+
 	public static void main(String[] args) {
-		generateGarbage();
-		
 		Map<String, Integer> map = new HashMap<>();
 		map.put("one", 1);
 		map.put("two", 2);
@@ -33,18 +31,15 @@ public static void main(String[] args) {
 		Map.Entry<String, Integer> entry = set.iterator().next();
 		entry.getKey();
 	}
-	
-	private static void generateGarbage() {
-		// generate garbage repeatedly to verify that logical values don't get GCed
-		Timer timer = new Timer(true);
-		timer.scheduleAtFixedRate(new TimerTask() {
-			private List<String> garbage;
-			@Override
-			public void run() {
-				System.gc();
-				garbage = Arrays.asList(new String("a"), new String("b"), new String("c"));
-			}
-		}, 200, 20);
+
+	// called from test to verify that logical values don't get GCed
+	private static void generateGarbageAndGC() throws InterruptedException {
+		List<Object> garbage;
+		for (int i = 0; i < 10; ++i) {
+			System.gc();
+			garbage = Arrays.asList(new Object(), new Object(), new Object());
+			Thread.sleep(20);
+		}
 	}
 
 }

org.eclipse.jdt.debug.tests/tests/org/eclipse/jdt/debug/tests/variables/TestLogicalStructures.java

@@ -13,17 +13,29 @@
  *******************************************************************************/
 package org.eclipse.jdt.debug.tests.variables;
 
+import java.io.PrintWriter;
+import java.io.StringWriter;
+import java.util.concurrent.atomic.AtomicBoolean;
+
+import org.eclipse.core.runtime.CoreException;
+import org.eclipse.debug.core.DebugEvent;
+import org.eclipse.debug.core.DebugException;
 import org.eclipse.debug.core.DebugPlugin;
 import org.eclipse.debug.core.ILogicalStructureType;
 import org.eclipse.debug.core.model.IBreakpoint;
 import org.eclipse.debug.core.model.IValue;
 import org.eclipse.debug.core.model.IVariable;
 import org.eclipse.jdt.debug.core.IJavaArray;
+import org.eclipse.jdt.debug.core.IJavaDebugTarget;
 import org.eclipse.jdt.debug.core.IJavaObject;
 import org.eclipse.jdt.debug.core.IJavaStackFrame;
 import org.eclipse.jdt.debug.core.IJavaThread;
 import org.eclipse.jdt.debug.core.IJavaVariable;
+import org.eclipse.jdt.debug.eval.IAstEvaluationEngine;
+import org.eclipse.jdt.debug.eval.IEvaluationListener;
+import org.eclipse.jdt.debug.eval.IEvaluationResult;
 import org.eclipse.jdt.debug.tests.AbstractDebugTest;
+import org.eclipse.jdt.internal.debug.core.JDIDebugPlugin;
 
 /**
  * Tests for logical structures
@@ -44,7 +56,7 @@ public TestLogicalStructures(String name) {
 	 */
 	public void testListLogicalStructure() throws Exception {
 		String typeName = "LogicalStructures";
-		createLineBreakpoint(34, typeName);
+		createLineBreakpoint(32, typeName);
 		IJavaThread thread= null;
 		try {
 			thread= launchToBreakpoint(typeName);
@@ -64,7 +76,7 @@ public void testListLogicalStructure() throws Exception {
 			assertEquals("Should be one logical structure type", 1, types.length);
 
 			IJavaObject logicalValue = (IJavaObject) types[0].getLogicalStructure(value);
-			Thread.sleep(500); // run a few GC cycles
+			gcInSnippet(frame);
 			assertEquals("Logical value should be an array", "java.lang.Object[]", logicalValue.getJavaType().getName());
 
 			IJavaArray array = (IJavaArray) logicalValue;
@@ -81,7 +93,7 @@ public void testListLogicalStructure() throws Exception {
 	 */
 	public void testMapLogicalStructure() throws Exception {
 		String typeName = "LogicalStructures";
-		createLineBreakpoint(34, typeName);
+		createLineBreakpoint(32, typeName);
 		IJavaThread thread= null;
 		try {
 			thread= launchToBreakpoint(typeName);
@@ -101,7 +113,7 @@ public void testMapLogicalStructure() throws Exception {
 			assertEquals("Should be one logical structure type", 1, types.length);
 
 			IJavaObject logicalValue = (IJavaObject) types[0].getLogicalStructure(value);
-			Thread.sleep(500); // run a few GC cycles
+			gcInSnippet(frame);
 			assertEquals("Logical value should be an array", "java.lang.Object[]", logicalValue.getJavaType().getName());
 
 			IJavaArray array = (IJavaArray) logicalValue;
@@ -118,7 +130,7 @@ public void testMapLogicalStructure() throws Exception {
 	 */
 	public void testEntryLogicalStructure() throws Exception {
 		String typeName = "LogicalStructures";
-		createLineBreakpoint(34, typeName);
+		createLineBreakpoint(32, typeName);
 		IJavaThread thread= null;
 		try {
 			thread= launchToBreakpoint(typeName);
@@ -138,15 +150,63 @@ public void testEntryLogicalStructure() throws Exception {
 			assertEquals("Should be one logical structure type", 1, types.length);
 
 			IJavaObject logicalValue = (IJavaObject) types[0].getLogicalStructure(value);
-			Thread.sleep(500); // run a few GC cycles
+			gcInSnippet(frame);
 			IVariable[] children = logicalValue.getVariables();
 			assertEquals("Should be two elements in the structure", 2, children.length);
 			assertEquals("First entry should be key", "key", children[0].getName());
 			assertEquals("Second entry should be value", "value", children[1].getName());
-
 		} finally {
 			terminateAndRemove(thread);
 			removeAllBreakpoints();
 		}
 	}
+
+	private void gcInSnippet(IJavaStackFrame stackFrame) throws CoreException, InterruptedException {
+		IAstEvaluationEngine engine = JDIDebugPlugin.getDefault().getEvaluationEngine(getProjectContext(), (IJavaDebugTarget) stackFrame.getDebugTarget());
+		EvaluationListener listener = new EvaluationListener();
+		engine.evaluate("generateGarbageAndGC()", stackFrame, listener, DebugEvent.EVALUATION_IMPLICIT, false);
+		listener.await();
+
+	}
+
+	private static class EvaluationListener implements IEvaluationListener {
+
+		private final AtomicBoolean done = new AtomicBoolean(false);
+		private final StringBuilder errors = new StringBuilder();
+
+		@Override
+		public void evaluationComplete(IEvaluationResult result) {
+			if (result.hasErrors()) {
+				errors.append("Evaluation resulted in errors:");
+				errors.append(System.lineSeparator());
+				for (String error : result.getErrorMessages()) {
+					errors.append(error);
+					errors.append(System.lineSeparator());
+				}
+				DebugException exception = result.getException();
+				if (exception != null) {
+					StringWriter sw = new StringWriter();
+					PrintWriter pw = new PrintWriter(sw);
+					exception.printStackTrace(pw);
+					errors.append(sw.getBuffer().toString());
+					errors.append(System.lineSeparator());
+				}
+			}
+			done.set(true);
+
+		}
+
+		private void await() throws InterruptedException {
+			long start = System.currentTimeMillis();
+			while (!done.get() && System.currentTimeMillis() - start <= DEFAULT_TIMEOUT) {
+				Thread.sleep(10);
+			}
+			if (!done.get()) {
+				fail("Timeout occurred while waiting on evaluation result");
+			}
+			if (!errors.isEmpty()) {
+				fail(errors.toString());
+			}
+		}
+	}
 }