Log4j1.2 --- 死锁

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#log4j #多线程 #apache #object #bt #api

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博客讲述了在使用Log4j1.2时遇到的死锁问题，主要原因是多个线程同时写日志导致争夺RootCategory对象的锁。文章提供了线程堆栈信息，揭示了死锁发生在`Category.callAppenders`方法上，且Apache尚未解决该古老bug。

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为嘛死锁无处不在啊？出问题的这个进程是做后台计算的，三十个左右的NodeThread，基本上在执行相同的http请求时，依赖的服务没有及时响应，等待一段时间后超时，于是线程们开始写日志。基本上等于三十个线程同时开始记日志，要求获取aorg.apache.log4j.spi.RootCategory 对象的锁。多线程环境下，真是啥都不牢靠。

众网友反映这个问题在log4j 1.2*版的古老bug。至今还没解决... apache说1.3是个不连续的版本，2.0是实验性质的版本，唉，不靠谱。

还有同学说有些死锁是有些应用层日志api调用得有问题，不是人log4j的问题，那同学代码确实写的很bt，但是和我碰到的问题不是一个问题，就不深入讨论了。 http://mail-archives.apache.org/mod_mbox/logging-log4j-user/200810.mbox/%3C48FC8556.7020804@corporater.com%3E

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有stack有真相。

一个线程

"Thread-2174" daemon prio=10 tid=0x00000000506a3000 nid=0x7a2 runnable [0x00000000452f8000]
   java.lang.Thread.State: RUNNABLE
        at java.io.FileOutputStream.writeBytes(Native Method)
        at java.io.FileOutputStream.write(FileOutputStream.java:260)
        at java.io.BufferedOutputStream.write(BufferedOutputStream.java:105)
        - locked <0x00002aaab3611fb0> (a java.io.BufferedOutputStream)
        at java.io.PrintStream.write(PrintStream.java:430)
        - locked <0x00002aaab3611f78> (a java.io.PrintStream)
        at sun.nio.cs.StreamEncoder.writeBytes(StreamEncoder.java:202)
        at sun.nio.cs.StreamEncoder.implFlushBuffer(StreamEncoder.java:272)
        at sun.nio.cs.StreamEncoder.implFlush(StreamEncoder.java:276)
        at sun.nio.cs.StreamEncoder.flush(StreamEncoder.java:122)
        - locked <0x00002aaab589f280> (a java.io.OutputStreamWriter)
        at java.io.OutputStreamWriter.flush(OutputStreamWriter.java:212)
        at org.apache.log4j.helpers.QuietWriter.flush(QuietWriter.java:49)
        at org.apache.log4j.WriterAppender.subAppend(WriterAppender.java:306)
        at org.apache.log4j.WriterAppender.append(WriterAppender.java:150)
        at org.apache.log4j.AppenderSkeleton.doAppend(AppenderSkeleton.java:221)
        - locked <0x00002aaab589e658> (a org.apache.log4j.ConsoleAppender)
        at org.apache.log4j.helpers.AppenderAttachableImpl.appendLoopOnAppenders(AppenderAttachableImpl.java:57)
        at org.apache.log4j.Category.callAppenders(Category.java:187)
        - locked <0x00002aaab5838af0> (a org.apache.log4j.spi.RootCategory)
        at org.apache.log4j.Category.forcedLog(Category.java:372)
        at org.apache.log4j.Category.info(Category.java:674)
        at com.wps.www.oaas.ftr.dispatcher.task.XLiveIndexWorker_Optimize.doIndex(XLiveIndexWorker_Optimize.java:278)
        at com.wps.www.oaas.ftr.dispatcher.task.XLiveIndexWorker_Optimize.doIndexes(XLiveIndexWorker_Optimize.java:185)
        at com.wps.www.oaas.ftr.dispatcher.task.XLiveTaskWorker.doWork(XLiveTaskWorker.java:23)
        at com.wps.www.oaas.ftr.dispatcher.node.NodeThread.doWork(NodeThread.java:256)
        at com.wps.www.oaas.ftr.dispatcher.node.NodeThread.run(NodeThread.java:185)

其它线程：

"Thread-2169" daemon prio=10 tid=0x0000000050ba0000 nid=0x6480 waiting for monitor entry [0x0000000044bf1000]
   java.lang.Thread.State: BLOCKED (on object monitor)
        at org.apache.log4j.Category.callAppenders(Category.java:185)
        - waiting to lock <0x00002aaab5838af0> (a org.apache.log4j.spi.RootCategory)
        at org.apache.log4j.Category.forcedLog(Category.java:372)
        at org.apache.log4j.Category.info(Category.java:674)
        at com.wps.www.oaas.ftr.dispatcher.task.XLiveIndexWorker_Optimize.doIndex(XLiveIndexWorker_Optimize.java:278)
        at com.wps.www.oaas.ftr.dispatcher.task.XLiveIndexWorker_Optimize.doIndexes(XLiveIndexWorker_Optimize.java:185)
        at com.wps.www.oaas.ftr.dispatcher.task.XLiveTaskWorker.doWork(XLiveTaskWorker.java:23)
        at com.wps.www.oaas.ftr.dispatcher.node.NodeThread.doWork(NodeThread.java:256)
        at com.wps.www.oaas.ftr.dispatcher.node.NodeThread.run(NodeThread.java:185)