死锁获取锁

Question

我有一个死锁的线程转储，我找不到原因。在第一次检查时，看起来有些客户端代码只是无法获得ReentrantLock上的锁，该锁是MyClass拥有的。

"qtp1450652220-77" Id=77 WAITING on java.util.concurrent.locks.ReentrantLock$NonfairSync@1e319fef owned by "pool-2-thread-2" Id=1651
    at sun.misc.Unsafe.park(Native Method)
    -  waiting on java.util.concurrent.locks.ReentrantLock$NonfairSync@1e319fef
    at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:870)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1199)
    at java.util.concurrent.locks.ReentrantLock$NonfairSync.lock(ReentrantLock.java:209)
    at java.util.concurrent.locks.ReentrantLock.lock(ReentrantLock.java:285)
    at com.mycode.MyClass.methodName(MyClass.java:1008)

但是，拥有线程的转储是：

"pool-2-thread-2" Id=1651 WAITING on java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject@56171f7a
    at sun.misc.Unsafe.park(Native Method)
    -  waiting on java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject@56171f7a
    at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
    at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
    at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1067)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1127)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)

    Number of locked synchronizers = 1
    - java.util.concurrent.locks.ReentrantLock$NonfairSync@1e319fef

毫无疑问，ReentrantLock上的锁列在底部。但令我惊讶的是，线程转储中没有我的客户端代码。没有迹象表明ReentrantLock最初是如何获得的，那么我该如何修复它呢？

MyClass中的代码是：

public Collection<String> methodName() {

    interruptLock.lock();
    try {
        /* do stuff */
        return tagsToReturn;
    } finally {
        interruptLock.unlock();
    }
}

第1008行是interruptLock.lock();行。

Answer 1

您可能必须使用j堆栈和-l选项捕获线程堆栈：

https://docs.oracle.com/javase/8/docs/technotes/tools/unix/jstack.html

-l 很长的名单。打印有关锁的其他信息，如拥有java.util.concurrent可拥有同步器的列表。参见AbstractOwnableSynchronizer类在http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/locks/AbstractOwnableSynchronizer.html中的描述