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/* *******************************************************************
* Copyright (c) 2004 IBM
* All rights reserved.
* This program and the accompanying materials are made available
* under the terms of the Eclipse Public License v1.0
* which accompanies this distribution and is available at
* https://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* Dmitry Mikhaylov - initial implementation
* ******************************************************************/
package org.aspectj.apache.bcel.classfile.tests;
import org.aspectj.apache.bcel.classfile.Code;
import org.aspectj.apache.bcel.classfile.JavaClass;
import org.aspectj.apache.bcel.classfile.LocalVariableTable;
import org.aspectj.apache.bcel.classfile.Method;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;
import java.util.concurrent.atomic.AtomicReference;
public class LocalVariableTableConcurrencyTest extends BcelTestCase {
private final int nThreads = Runtime.getRuntime().availableProcessors();
private final ExecutorService[] workers = new ExecutorService[nThreads];
private LocalVariableTable reference;
protected void setUp() throws Exception {
super.setUp();
for (int i = 0; i < nThreads; i++) workers[i] = Executors.newSingleThreadExecutor();
JavaClass clazz = getClassFromJar("SimpleGenericsProgram");
Method mainMethod = getMethod(clazz,"main");
Code codeAttr = (Code) findAttribute("Code",mainMethod.getAttributes());
reference = (LocalVariableTable) findAttribute("LocalVariableTable",codeAttr.getAttributes());
}
/**
* Try to hit concurrency bug in org.aspectj.apache.bcel.classfile.LocalVariableTable.unpack().
* We do so by running unpack() on same instance with multiple threads, and artificially
* delaying all threads but first so that they enter unpack() the moment first thread is about to leave it.
*
* Since this test relies on empirically obtained access pattern and number of iterations,
* it never has 100% probability of hitting the bug. If it fails - there is certainly a bug.
* If it passes, it could mean anything - fully correct code or slightly changed execution order preventing
* threads to collide at problematic location.
*
* As such, it is not really good for unit testing.
*/
public void testLocalVariableTableAttributeConcurrency() throws RuntimeException, InterruptedException {
final AtomicReference<RuntimeException> error = new AtomicReference<>();
for (int i = 0; i < 10000; i++) {
LocalVariableTable sharedInstance = reference.copyFromPackedState();
CountDownLatch preStart = new CountDownLatch(nThreads);
Semaphore start = new Semaphore(0);
CountDownLatch finish = new CountDownLatch(nThreads);
for (int j = 0; j < nThreads; j++) {
final boolean needsDelay = j > 0;
workers[j].execute(() -> {
preStart.countDown();
start.acquireUninterruptibly();
// trying to trigger concurrent unpacking bug - one tread should enter unpack() when other is about to leave it
if (needsDelay) reference.copyFromPackedState().getTableLength();
try {
sharedInstance.getTableLength();
}
catch (RuntimeException ex) {
error.compareAndSet(null, ex);
}
finish.countDown();
});
}
preStart.await();
start.release(nThreads);
finish.await();
if (error.get() != null) throw error.get();
}
}
protected void tearDown() throws Exception {
for (int i = 0; i < nThreads; i++) if (workers[i] != null) workers[i].shutdownNow();
super.tearDown();
}
}
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