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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (GROOVY-8067) Possible deadlock when creating new ClassInfo entries in the cache
Date Wed, 08 Feb 2017 20:35:41 GMT

    [ https://issues.apache.org/jira/browse/GROOVY-8067?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15858505#comment-15858505
] 

ASF GitHub Bot commented on GROOVY-8067:
----------------------------------------

Github user jwagenleitner commented on a diff in the pull request:

    https://github.com/apache/groovy/pull/489#discussion_r100162935
  
    --- Diff: subprojects/stress/src/test/java/org/codehaus/groovy/reflection/ClassInfoDeadlockStressTest.java
---
    @@ -0,0 +1,140 @@
    +/*
    + *  Licensed to the Apache Software Foundation (ASF) under one
    + *  or more contributor license agreements.  See the NOTICE file
    + *  distributed with this work for additional information
    + *  regarding copyright ownership.  The ASF licenses this file
    + *  to you 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.codehaus.groovy.reflection;
    +
    +import groovy.lang.GroovyClassLoader;
    +
    +import java.util.concurrent.CountDownLatch;
    +import java.util.concurrent.TimeUnit;
    +import java.util.concurrent.atomic.AtomicInteger;
    +
    +import org.apache.groovy.stress.util.GCUtils;
    +import org.junit.Test;
    +import static org.junit.Assert.*;
    +
    +/**
    + * Tests for deadlocks in the ClassInfo caching.
    + *
    + */
    +public class ClassInfoDeadlockStressTest {
    +
    +    private static final int DEADLOCK_TRIES = 8;
    +    private static final int THREAD_COUNT = 8;
    +
    +    private final CountDownLatch startLatch = new CountDownLatch(1);
    +    private final CountDownLatch completeLatch = new CountDownLatch(THREAD_COUNT);
    +    private final GroovyClassLoader gcl = new GroovyClassLoader();
    +    private final AtomicInteger counter = new AtomicInteger();
    +
    +    /**
    +     * We first generate a large number of ClassInfo instances for classes
    +     * that are no longer reachable.  Then queue up threads to all request
    +     * ClassInfo instances for new classes simultaneously to ensure that
    +     * clearing the old references wont deadlock the creation of new
    +     * instances.
    +     * <p>
    +     * GROOVY-8067
    +     */
    +    @Test
    +    public void testDeadlock() throws Exception {
    +        for (int i = 1; i <= DEADLOCK_TRIES; i++) {
    +            System.out.println("Test Number: " + i);
    +            generateGarbage();
    +            GCUtils.gc();
    +            attemptDeadlock(null);
    +        }
    +    }
    +
    +    @Test
    +    public void testRequestsForSameClassInfo() throws Exception {
    +        Class<?> newClass = createRandomClass();
    +        for (int i = 1; i <= DEADLOCK_TRIES; i++) {
    +            System.out.println("Test Number: " + i);
    +            generateGarbage();
    +            GCUtils.gc();
    +            attemptDeadlock(newClass);
    +        }
    +        ClassInfo newClassInfo = ClassInfo.getClassInfo(newClass);
    +        for (ClassInfo ci : ClassInfo.getAllClassInfo()) {
    +            if (ci.getTheClass() == newClass && ci != newClassInfo) {
    +                fail("Found multiple ClassInfo instances for class");
    +            }
    +        }
    +    }
    +
    +    private void attemptDeadlock(final Class<?> cls) throws Exception {
    +        for (int i = 0; i < THREAD_COUNT; i++) {
    +            Runnable runnable = new Runnable() {
    +                @Override
    +                public void run() {
    +                    Class<?> newClass = (cls == null) ? createRandomClass() : cls;
    +                    try {
    +                        startLatch.await();
    +                    } catch (InterruptedException ie) {
    --- End diff --
    
    can use `ThreadUtils.awaite()`


> Possible deadlock when creating new ClassInfo entries in the cache
> ------------------------------------------------------------------
>
>                 Key: GROOVY-8067
>                 URL: https://issues.apache.org/jira/browse/GROOVY-8067
>             Project: Groovy
>          Issue Type: Bug
>          Components: groovy-runtime
>    Affects Versions: 2.4.8
>            Reporter: John Wagenleitner
>            Priority: Critical
>         Attachments: ClassInfoDeadlockTest.java
>
>
> When running Groovy without {{-Dgroovy.use.classvalue=true}} the ClassInfo instances
are cached in a {{ManagedConcurrentMap}} (MCM).  New values are computed on demand and computation
involves both a lock on a segment within the MCM and a lock on the {{GlobalClassSet}} (GCS)
which is backed by a {{ManagedLinkedList}}.  The problem is that both the ManagedConcurrentMap
and the GlobalClassSet share the same ReferenceQueue.
> Assume there is an enqueued {{ClassInfo}} value that is stored in Segment2 of the MCM.
 Now assume that Thread1 and Thread2 both request {{ClassInfo.getClassInfo(..)}} for two different
classes that do not currently exist in the cache.  Assume that based on hashing Thread1 gets
a lock on Segment1 and Thread2 gets a lock on Segment2.  Assume that Thread1 is the first
to call computeValue which in turn calls {{GlobalClassSet.add(..)}}.  This call adds a new
value to a {{ManagedLinkedList}}, and since it's managed the add operation will process the
ReferenceQueue. So Thread1 will attempt to dequeue the ClassInfo and the finalizeReference
method on it's entry will attempt to remove it from Segment2. Thread2 holds the lock for Segment2
and Thread2 is blocked and can't progress it's waiting on the the lock Thread1 holds the lock
for the GlobalClassSet, so deadlock occurs.
> The attached test case includes a thread dump at the bottom.



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