调试Hibernate/Ehcache死锁

Question

我们正在使用Ehcache版本2.4.4和Hibernate 3.5.5-FINAL.我的调试环境发生了一个奇怪的情况 - 看起来Ehcache陷入了僵局.这是堆栈跟踪的相关位:

http-8080-2@7345 daemon, prio=5, in group 'main', status: 'WAIT'
      at sun.misc.Unsafe.park(Unsafe.java:-1)
      at java.util.concurrent.locks.LockSupport.park(LockSupport.java:158)
      at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:811)
      at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireQueued(AbstractQueuedSynchronizer.java:842)
      at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquire(AbstractQueuedSynchronizer.java:1178)
      at java.util.concurrent.locks.ReentrantReadWriteLock$WriteLock.lock(ReentrantReadWriteLock.java:807)
      at net.sf.ehcache.store.compound.Segment.put(Segment.java:427)
      at net.sf.ehcache.store.compound.CompoundStore.put(CompoundStore.java:141)
      at net.sf.ehcache.Cache.putInternal(Cache.java:1434)
      at net.sf.ehcache.Cache.put(Cache.java:1367)
      at net.sf.ehcache.Cache.put(Cache.java:1339)
      at net.sf.ehcache.constructs.EhcacheDecoratorAdapter.put(EhcacheDecoratorAdapter.java:111)
      at net.sf.ehcache.hibernate.regions.EhcacheTransactionalDataRegion.put(EhcacheTransactionalDataRegion.java:127)
      at net.sf.ehcache.hibernate.strategy.NonStrictReadWriteEhcacheEntityRegionAccessStrategy.putFromLoad(NonStrictReadWriteEhcacheEntityRegionAccessStrategy.java:66)
      at net.sf.ehcache.hibernate.nonstop.NonstopAwareEntityRegionAccessStrategy.putFromLoad(NonstopAwareEntityRegionAccessStrategy.java:180)
      at org.hibernate.engine.TwoPhaseLoad.initializeEntity(TwoPhaseLoad.java:180)
      at org.hibernate.loader.Loader.initializeEntitiesAndCollections(Loader.java:898)
      at org.hibernate.loader.Loader.doQuery(Loader.java:773)
      at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:270)
      at org.hibernate.loader.Loader.loadEntity(Loader.java:1953)
      at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:86)
      at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:76)
      at org.hibernate.persister.entity.AbstractEntityPersister.load(AbstractEntityPersister.java:3270)
      at org.hibernate.event.def.DefaultLoadEventListener.loadFromDatasource(DefaultLoadEventListener.java:496)
      at org.hibernate.event.def.DefaultLoadEventListener.doLoad(DefaultLoadEventListener.java:477)
      at org.hibernate.event.def.DefaultLoadEventListener.load(DefaultLoadEventListener.java:227)
      at org.hibernate.event.def.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:147)
      at org.hibernate.impl.SessionImpl.fireLoad(SessionImpl.java:1080)
      at org.hibernate.impl.SessionImpl.immediateLoad(SessionImpl.java:1018)
      at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:176)
      at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:215)
      at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:191)
      at vyre.content.items.ItemInfo_$$_javassist_87.equals(ItemInfo_$$_javassist_87.java:-1)
      at org.hibernate.util.EqualsHelper.equals(EqualsHelper.java:33)
      at org.hibernate.type.AbstractType.isEqual(AbstractType.java:132)
      at org.hibernate.type.ComponentType.isEqual(ComponentType.java:153)
      at org.hibernate.cache.CacheKey.equals(CacheKey.java:79)
      at net.sf.ehcache.store.compound.Segment.containsKey(Segment.java:279)
      at net.sf.ehcache.store.compound.CompoundStore.containsKey(CompoundStore.java:353)
      at net.sf.ehcache.store.compound.impl.MemoryOnlyStore.containsKeyInMemory(MemoryOnlyStore.java:121)
      at net.sf.ehcache.Cache.searchInStoreWithStats(Cache.java:1884)
      at net.sf.ehcache.Cache.get(Cache.java:1549)
      at net.sf.ehcache.constructs.EhcacheDecoratorAdapter.get(EhcacheDecoratorAdapter.java:75)
      at net.sf.ehcache.hibernate.regions.EhcacheTransactionalDataRegion.get(EhcacheTransactionalDataRegion.java:105)
      at net.sf.ehcache.hibernate.strategy.NonStrictReadWriteEhcacheEntityRegionAccessStrategy.get(NonStrictReadWriteEhcacheEntityRegionAccessStrategy.java:55)
      at net.sf.ehcache.hibernate.nonstop.NonstopAwareEntityRegionAccessStrategy.get(NonstopAwareEntityRegionAccessStrategy.java:122)
      at org.hibernate.event.def.DefaultLoadEventListener.loadFromSecondLevelCache(DefaultLoadEventListener.java:586)
      at org.hibernate.event.def.DefaultLoadEventListener.doLoad(DefaultLoadEventListener.java:459)
      at org.hibernate.event.def.DefaultLoadEventListener.load(DefaultLoadEventListener.java:227)
      at org.hibernate.event.def.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:147)
      at org.hibernate.impl.SessionImpl.fireLoad(SessionImpl.java:1080)
      at org.hibernate.impl.SessionImpl.immediateLoad(SessionImpl.java:1018)
      at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:176)
      at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:215)
      at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:191)
      at vyre.content.items.Item_$$_javassist_102.getName(Item_$$_javassist_102.java:-1)
      at sun.reflect.NativeMethodAccessorImpl.invoke0(NativeMethodAccessorImpl.java:-1)
      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
      at java.lang.reflect.Method.invoke(Method.java:597)
      at org.apache.velocity.runtime.parser.node.PropertyExecutor.execute(PropertyExecutor.java:142)
      at org.apache.velocity.util.introspection.UberspectImpl$VelGetterImpl.invoke(UberspectImpl.java:533)
      at org.apache.velocity.runtime.parser.node.ASTIdentifier.execute(ASTIdentifier.java:198)
      at org.apache.velocity.runtime.parser.node.ASTReference.execute(ASTReference.java:252)
      at org.apache.velocity.runtime.parser.node.ASTReference.render(ASTReference.java:332)
      at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:336)
      at org.apache.velocity.runtime.RuntimeInstance.render(RuntimeInstance.java:1277)
      at org.apache.velocity.runtime.RuntimeInstance.evaluate(RuntimeInstance.java:1216)
      at org.apache.velocity.runtime.RuntimeInstance.evaluate(RuntimeInstance.java:1165)
      at org.apache.velocity.app.Velocity.evaluate(Velocity.java:191)
      at org.apache.jsp.WEB_002dINF.jsp.pub_005fmodule.taglibs.contentTemplate.search.itemLink_jsp._jspService(itemLink.jsp:36)

  (...another hundred or so irrelevant stack trace fragments skipped...)

这就是我了解情况的方式:

• 堆栈底部从Apache Velocity进行评估开始,并传递给Hibernate代理对象
• 此对象缓存<cache usage="nonstrict-read-write"/>并具有复合键
• Hibernate尝试从缓存中获取实体
• Hibernate/Ehcache检查对象的相等性(注意:equals永远不会执行"真实" 方法)
• 等号检查返回false,Hibernate正在加载对象
• 加载成功后,对象就会被放入缓存中
• 僵局？

违规的代码片段如下所示:

net.sf.ehcache.store.compound.Segment.put(Segment.java:427) 

423 Element put(Object key, int hash, Element element, boolean onlyIfAbsent) { 
424    boolean installed = false; 
425    Object encoded = create(key, element); 
426 
427    writeLock().lock(); 
428    try { 
429       // ensure capacity 
430       if (count + 1 > threshold) { 

我可以访问该encoded对象,但它看起来writeLock()已经被获取,因此整个线程被卡住了.这是我的力量结束的地方,因为我对Ehcache的内部知之甚少Segment.

任何人都可以提供有关如何进一步调试的提示吗？不幸的是,创建一个小的,自洽的测试用例不是一种选择.

这也发布在Ehcache论坛页面上.

提前致谢.

Answer 1

回答我自己的问题以防万一其他人滑倒这个并且Ehcache论坛中的帖子将会消失.

原因:
死锁的原因来自同一个线程,其中尝试在缓存中找到对象.在该堆的底部部分中的一个,是了Ehcache做readLock().lock()和writeLock().lock()相同的锁定对象上.这显然是禁忌.

为什么会这样？ 发生这种情况是因为缓存正在加载另一个对象作为副作用(另一个大禁忌),并且两个对象都在同一个内存段中结束(因此共享相同ReentrantLock).提示:我使用相同的缓存区域,因为我不想为数百种不同的实体类型指定容量.

为什么会这样？ 由于我的Hibernate映射,无意中加载了缓存键查找.对象(正在查找)有一个复合键,引用另一个对象.该复合键的一部分已在该equals方法中使用并导致该负载.巧合的是,还尝试将加载的对象放置在同一缓存段中 - 并导致死锁.

经验教训对Hibernate映射
要格外小心.如果您有复合键,请不要使用,<key-many-to-one因为这会导致不可预测的结果.我想很多人没有意识到这一点,只是因为他们将不同类型的对象放入不同的缓存区域,但是无意中的负载仍然是邪恶的.

所有积分都来自Terracotta论坛的Alex,以帮助我找到这个.