Java并发性:导致StackOverflowError异常的同步语句/方法

Question

我正在强调--在Java中测试一个事件回调处理框架，该框架在可能的情况下大量使用并发性，从而在可能发生数据竞争时使用同步方法和语句。在一个名为testDispatchWorstCase的恰当命名的单元测试中，将同时启动100个到500个线程，每个线程都使用同步语句调用方法，这些语句利用一个名为MasterSemaphore的控制器对象的监视器。在用100个线程进行测试时，有时一切都很完美，有时我在一个或多个同步语句和/或方法中遇到堆栈溢出异常。在使用500个线程进行测试时，我几乎总是在一个或多个同步语句和/或方法中遇到堆栈溢出异常。

MasterSemaphore提供了用于锁定同步语句的监视器，并提供了一些事件处理方法，这些方法被调用以协调不同线程对资源的访问。有鉴于此，我想可能使用MasterSemaphore的一个成员对象，该对象没有其他职责，因为监视器提供程序将解决问题--不幸的是，这只会导致死锁；数百个线程被困在eclipse的调试器线程视图中的“监视器”状态，并且永远保持这种状态。我的问题如下：

1. 对象的监视器如何存储和跟踪对受此监视器锁约束的线程的引用？
2. 为什么我会使用监视器提供程序的MasterSemaphore成员对象陷入死锁？是否需要在同步语句中显式调用wait...notifyAll？
3. 当数百个线程受制于一个对象的监视器锁时，会导致同步语句中的堆栈溢出吗？

堆栈跟踪是：

01-02 07:47:44.910 27698 27842 E AndroidRuntime: FATAL EXCEPTION: HPCHead Spawned 
Thread #24

01-02 07:47:44.910 27698 27842 E AndroidRuntime: java.lang.StackOverflowError

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at   
java.lang.AbstractStringBuilder.append0(AbstractStringBuilder.java:147)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
java.lang.IntegralToString.convertInt(IntegralToString.java:209)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
java.lang.IntegralToString.appendInt(IntegralToString.java:173)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
java.lang.StringBuilder.append(StringBuilder.java:139)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
java.lang.Thread.toString(Thread.java:1098)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.MasterSemaphore.
addRegistrantForCallback_PrefabEventHandling(MasterSemaphore.java:2524)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.MasterEventHandler$EventIDFreedHandler.
onUpdateNeeded(MasterEventHandler.java:221)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at     
com.hdradio.hdradiomanagerjc.hpc.CallbackDataRecord.
postToQueueHead(CallbackDataRecord.java:107)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.MasterSemaphore.
onFinishedEventProcessing(MasterSemaphore.java:1219)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.MasterSemaphore.
addRegistrantForCallback_PrefabEventHandling(MasterSemaphore.java:2597)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.MasterEventHandler$EventIDFreedHandler.
onUpdateNeeded(MasterEventHandler.java:221)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.CallbackDataRecord.
postToQueueHead(CallbackDataRecord.java:107)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.MasterSemaphore.
onFinishedEventProcessing(MasterSemaphore.java:1219)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.MasterSemaphore.
addRegistrantForCallback_PrefabEventHandling(MasterSemaphore.java:2597)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.MasterEventHandler$EventIDFreedHandler
.onUpdateNeeded(MasterEventHandler.java:221)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.CallbackDataRecord.
postToQueueHead(CallbackDataRecord.java:107)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.MasterSemaphore.
onFinishedEventProcessing(MasterSemaphore.java:1219)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.MasterSemaphore.
addRegistrantForCallback_PrefabEventHandling(MasterSemaphore.java:2597)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.MasterEventHandler$EventIDFreedHandler.
onUpdateNeeded(MasterEventHandler.java:221)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.CallbackDataRecord.
postToQueueHead(CallbackDataRecord.java:107)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.MasterSemaphore.
onFinishedEventProcessing(MasterSemaphore.java:1219)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.MasterSemaphore.
addRegistrantForCallback_PrefabEventHandling(MasterSemaphore.java:2597)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.MasterEventHandler$EventIDFreedHandler.
onUpdateNeeded(MasterEventHandler.java:221)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.CallbackDataRecord.
postToQueueHead(CallbackDataRecord.java:107)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.MasterSemaphore.
onFinishedEventProcessing(MasterSemaphore.java:1219)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.MasterSemaphore.
addRegistrantForCallback_PrefabEventHandling(MasterSemaphore.java:2597)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.MasterEventHandler$EventIDFreedHandler.
onUpdateNeeded(MasterEventHandler.java:221)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.CallbackDataRecord.
postToQueueHead(CallbackDataRecord.java:107)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.MasterSemaphore.
onFinishedEventProcessing(MasterSemaphore.java:1219)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.MasterSemaphore.
addRegistrantForCallback_PrefabEventHandling(MasterSemaphore.java:2597)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.MasterEventHandler$EventIDFreedHandler.
onUpdateNeeded(MasterEventHandler.java:221)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.CallbackDataRecord.
postToQueueHead(CallbackDataRecord.java:107)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.MasterSemaphore.
onFinishedEventProcessing(MasterSemaphore.java:1219)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.MasterSemaphore.
addRegistrantForCallback_PrefabEventHandling(MasterSemaphore.java:2597)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.MasterEventHandler$EventIDFreedHandler.
onUpdateNeeded(MasterEventHandler.java:221)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.CallbackDataRecord.
postToQueueHead(CallbackDataRecord.java:107)

01-02 07:47:44.910 27698 27842 E AndroidRuntime:    at 
com.hdradio.hdradiomanagerjc.hpc.MasterSemaphore.
onFinishedEventProcessing(MasterSemaphore.java:1219)

Answer 1

对你的问题的回答：

1. 这是一个描述如何使用对象监视器进行同步的文章。
2. 我不知道你为什么会陷入僵局。我需要看到更多的代码才能帮上忙。不过，正如我在前面的评论中所说的，您不需要使用wait'/notifyAllwhen usingsynchronized. The JVM handles all the locking and waiting automatically for you. Of course, this doesn't mean that you can't program yourself into a deadlock situation (that's actually pretty easy to do). Addingnotify()`调用不会取消死锁。
3. 所以堆栈溢出问题来自一个递归调用堆栈，如下所示： ..。 MasterSemaphore.onFinishedEventProcessing(MasterSemaphore.java:1219) MasterSemaphore.addRegistrantForCallback_PrefabEventHandling(MasterSemaphore.java:2597) MasterEventHandler$EventIDFreedHandler.onUpdateNeeded(MasterEventHandler.java:221) CallbackDataRecord.postToQueueHead(CallbackDataRecord.java:107) MasterSemaphore.onFinishedEventProcessing(MasterSemaphore.java:1219)

因此，onFinishedEventProcessing()被递归地调用，这导致堆栈溢出。您应该看看为什么会发生这种情况(如果需要的话添加一些日志记录)。