java - Java 线程转储中的 "Lock released while waiting:"是什么意思？

Question

在此线程转储中:

INFO   | jvm 3    | 2011/06/08 13:36:12 | "ExecuteThread: '38' for queue: 'default'" id=55 idx=0x78 tid=5316 prio=5 alive, in native, waiting, daemon
INFO   | jvm 3    | 2011/06/08 13:36:12 |     -- Waiting for notification on: weblogic/ejb20/locks/ExclusiveLockManager$LockWaiter@0x25EF8828[fat lock]
INFO   | jvm 3    | 2011/06/08 13:36:12 |     at jrockit/vm/Threads.waitForSignal(J)Z(Native Method)
INFO   | jvm 3    | 2011/06/08 13:36:12 |     at java/lang/Object.wait(J)V(Native Method)[optimized]
INFO   | jvm 3    | 2011/06/08 13:36:12 |     at weblogic/ejb20/locks/ExclusiveLockManager$LockBucket.lock(Ljava/lang/Object;Ljava/lang/Object;I)Z(ExclusiveLockManager.java:504)[optimized]
INFO   | jvm 3    | 2011/06/08 13:36:12 |     ^-- Lock released while waiting: weblogic/ejb20/locks/ExclusiveLockManager$LockWaiter@0x25EF8828[fat lock]
INFO   | jvm 3    | 2011/06/08 13:36:12 |     at weblogic/ejb20/locks/ExclusiveLockManager.lock(Ljava/lang/Object;Ljava/lang/Object;I)Z(ExclusiveLockManager.java:261)[optimized]
INFO   | jvm 3    | 2011/06/08 13:36:12 |     at weblogic/ejb20/manager/ExclusiveEntityManager.acquireLock(Ljava/lang/Object;Ljavax/transaction/Transaction;I)Z(ExclusiveEntityManager.java:210)[inlined]
INFO   | jvm 3    | 2011/06/08 13:36:12 |     at weblogic/ejb20/manager/ExclusiveEntityManager.getReadyBean(Ljava/lang/Object;Ljavax/transaction/Transaction;I)Ljavax/ejb/EntityBean;(ExclusiveEntityManager.java:267)[inlined]
INFO   | jvm 3    | 2011/06/08 13:36:12 |     at weblogic/ejb20/manager/ExclusiveEntityManager.preInvoke(Lweblogic/ejb20/internal/InvocationWrapper;)Ljavax/ejb/EnterpriseBean;(ExclusiveEntityManager.java:242)[optimized]
INFO   | jvm 3    | 2011/06/08 13:36:12 |     at weblogic/ejb20/internal/BaseEJBObject.preInvoke(Lweblogic/ejb20/internal/InvocationWrapper;Lweblogic/security/service/ContextHandler;)Lweblogic/ejb20/internal/InvocationWrapper;(BaseEJBObject.java:152)[inlined]
INFO   | jvm 3    | 2011/06/08 13:36:12 |     at weblogic/ejb20/internal/EntityEJBObject.preInvoke(Lweblogic/ejb20/internal/MethodDescriptor;Lweblogic/security/service/ContextHandler;)Lweblogic/ejb20/internal/InvocationWrapper;(EntityEJBObject.java:104)[inlined]
INFO   | jvm 3    | 2011/06/08 13:36:12 |     at foob/ejb/commodity/ejb_Commodity_etfd4i_EOImpl.getData()Lfoob/ejb/commodity/db/CommodityData;(ejb_Commodity_etfd4i_EOImpl.java:701)[optimized]
INFO   | jvm 3    | 2011/06/08 13:36:12 |     at foob/ejb/item/OurItem.loadCommodityData()V(OurItem.java:172)[optimized]
INFO   | jvm 3    | 2011/06/08 13:36:12 |     ^-- Holding lock: java/lang/Class@0x067EA070[fat lock]
INFO   | jvm 3    | 2011/06/08 13:36:12 |     at foob/ejb/item/OurItem.getCommodityData()Lfoob/ejb/commodity/db/CommodityData;(OurItem.java:251)
INFO   | jvm 3    | 2011/06/08 13:36:12 |     at foob/ejb/item/OurItem.getTheControlGid()Ljava/lang/String;(OurItem.java:259)
INFO   | jvm 3    | 2011/06/08 13:36:12 |     at foob/business/shipment/OurThing.getTheControlGid(Lfoob/util/jdbc/OurConnection;)Ljava/lang/String;(OurThing.java:379)

行是什么

Lock released while waiting: weblogic/ejb20/locks/ExclusiveLockManager$LockWaiter@0x25EF8828

是什么意思？我们有 8 个其他线程阻塞等待 java/lang/Class@0x067EA070 被释放，这个线程持有，但我不明白这个线程阻塞了什么，也不知道这意味着什么锁被释放了。我本以为线程转储是一种停止世界类型的事件，因此有问题的行不会指在线程转储发生时释放的锁......

此外，它出现的位置是否有任何意义(即它上方和下方的线)？

显然我不是 Java 期望值，所以我希望这不是一个太愚蠢的问题。感谢您的帮助!

Answer 1

来自Oracle JRockit JDK Tools Guide ,

The semantics for waiting (for notification) for an object in Java is somewhat complex. First, to enter a synchronized block, you must take the lock for the object, and then you call wait() on that object. In the wait method, the lock is released before the thread goes to sleep waiting for a notification. When the thread receives a notification, wait() re-takes the lock before returning. If a thread has taken a lock, and is waiting for notification about that lock, the line in the stack trace that describes when the lock was taken is not shown as (Holding lock); it is shown as (Lock released while waiting.)

换句话说，这意味着所述线程有一个对象，该对象早些时候获得了一个锁，然后在调用 object.wait() 时释放了它。类似行为的代码模式是:

synchronized(lock) //acquires the lock
{
   ...
   do some work
   ...
   object.wait(); //releases the lock, and waits for a notification
}

更新

在查看堆栈跟踪时，您似乎正在使用实体 EJB Bean，并且考虑到此类实现的运行方式，通常会在实体 EJB 上获取锁。这实际上取决于 concurrency strategy用于管理必须访问数据库的并发事务。我会怀疑 bean 的数量太少，或者只有一个 bean 可以锁定。