was宕机常见问题及参考解决方案

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1、WAS宕机问题总结起来有以下几类：一、线程挂起导致线程池满（ThreadHang）:HangsrefertotheJVMlockinguporrefusingtorespond.Ahangcanoccurwhen:1）Yourapplicationenteredanwaitleak2）ExcessiveSynchronizationcauseperformanceproblems3）Adeadlockhasoccurred收集日志：生成JAVACORE分析工具：IBMThreadandMonitorDumpAnalyzer1、线程等待泄漏(W

2、aitLeaks)常见的情况就是，有很多线程使用wait()方法，等待被唤醒notify（）。但是，存在某一个线程获取到锁并且进行业务处理完成后，忘记去唤醒等待执行的进程。这样导致的等待泄漏，从而线程挂起。Whenyouusethewait/notifymechanism,youtypicallyhaveoneormorethreadsblockedinthewait()call,waitingtobenotified.Thenotifyingthreadissupposedtocallnotify()ornotifyAll()tosigna

3、lthatwaitingthreadscanwakeupandcarryonprocessing.Aproblmaticsituationcouldoccurthatthenotify()callisinvokedbeforethethreadsgointothewait()method.Inthiscase,thewaitingthreadswouldnotbenotifiedanymoreandbecomestuck.So,donotforgettonotifythewaitingtheadsinyouapplicationandmaks

4、surethattheNotifyactionisperformedafterallthewaitingthreadsarestarted.应对策略：notify必须发生在所有wait之前。2、同步过度（ExcessiveSynchronization）LIS系统FORMULAONE报表打印就是采用了SYNCHRONIZE思想，如果有某一个大的报表长时间打不出来的话，会导致其它所有的报表打印线程全部挂起。Synchronizationisrequiredforprotectingsomecriticalresources,butiflarge

5、sectionsofcodearesynchronized,anapplicationeffectivelywillbecomesinglethreaded,andthethroughputwilldecreasedramatically.Toimprovetheperformance,youshouldthinkabout:1)Useotherefficientalgorithmtoreplacethemonitor/lock?2)Trytokeepthemonitorlockforashorttime?3)Reducethenumbero

6、fthreadsusingthismonitor/lock?应对策略：改变程序实现算法，避免占用锁时间过长。比如设置多个锁或者提高同步代码块的执行效率。3、资源抢占死锁（DeadLock）线程运行需要获取到两个资源，当线程1获取到资源A，线程2获取到资源B，此时，线程1需要再获取资源B，线程2需要再获取资源A。这就形成了资源循环申请的一个死锁。其它想获取到资源A或者资源B的线程必将都会挂起。Inthiscase,athreadacquiresthelockonlock1,Atthesametime,anotherthreadacquirest

7、helockonlock2.sothethreadsaredeadlocked:neitherthreadwillgiveupitslockuntilitacquirestheotherlock,butneitherwillbeabletoacquiretheotherlockuntiltheotherthreadgivesitup.Oneofthebestwaystopreventthepotentialfordeadlockistoavoidacquiringmorethanonelockatatime,whichisoftenpract

8、ical.However,ifthatisnotpossible,youneedastrategythatensuresyouacquiremultiplelock