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我正在调试一个 GWT Web 应用程序，该应用程序在运行一段时间后已经耗尽 permgen 空间，并在 VisualVM 的线程转储中注意到有 248 个进程等待锁定相同的 StringBuffer，例如：

2013-02-27 10:56:30
Full thread dump Java HotSpot(TM) 64-Bit Server VM (23.3-b01 mixed mode):

"Attach Listener" daemon prio=10 tid=0x00007f3bdc00f000 nid=0x3bee waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:
    - None

"1301161716@qtp-1875293347-251" prio=10 tid=0x00007f3ba8209800 nid=0x301f waiting for monitor entry [0x00007f3b6a15f000]
   java.lang.Thread.State: BLOCKED (on object monitor)
    at org.mortbay.log.StdErrLog.warn(StdErrLog.java:128)
    - waiting to lock <0x0000000087b405c8> (a java.lang.StringBuffer)
    at org.mortbay.jetty.handler.ContextHandler$SContext.log(ContextHandler.java:1424)
    at com.google.gwt.user.server.rpc.RPCServletUtils.writeResponseForUnexpectedFailure(RPCServletUtils.java:389)
    at com.google.gwt.user.server.rpc.AbstractRemoteServiceServlet.doUnexpectedFailure(AbstractRemoteServiceServlet.java:110)
    at com.google.gwt.user.server.rpc.AbstractRemoteServiceServlet.doPost(AbstractRemoteServiceServlet.java:67)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)
    at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
    at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:401)
    at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
    at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
    at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:766)
    at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:450)
    at org.mortbay.jetty.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:230)
    at org.mortbay.jetty.handler.HandlerCollection.handle(HandlerCollection.java:114)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.Server.handle(Server.java:326)
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
    at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:945)
    at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:756)
    at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
    at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:410)
    at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)

   Locked ownable synchronizers:
    - None

"182760474@qtp-1875293347-250" prio=10 tid=0x00007f3ba8207800 nid=0x2ff7 waiting for monitor entry [0x00007f3b6a260000]
   java.lang.Thread.State: BLOCKED (on object monitor)
    at org.mortbay.log.StdErrLog.warn(StdErrLog.java:128)
    - waiting to lock <0x0000000087b405c8> (a java.lang.StringBuffer)
    at org.mortbay.jetty.handler.ContextHandler$SContext.log(ContextHandler.java:1424)
    at com.google.gwt.user.server.rpc.RPCServletUtils.writeResponseForUnexpectedFailure(RPCServletUtils.java:389)
    at com.google.gwt.user.server.rpc.AbstractRemoteServiceServlet.doUnexpectedFailure(AbstractRemoteServiceServlet.java:110)
    at com.google.gwt.user.server.rpc.AbstractRemoteServiceServlet.doPost(AbstractRemoteServiceServlet.java:67)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)
    at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
    at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:401)
    at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
    at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
    at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:766)
    at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:450)
    at org.mortbay.jetty.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:230)
    at org.mortbay.jetty.handler.HandlerCollection.handle(HandlerCollection.java:114)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.Server.handle(Server.java:326)
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
    at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:945)
    at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:756)
    at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
    at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:410)
    at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)

   Locked ownable synchronizers:
    - None

"1468146634@qtp-1875293347-249" prio=10 tid=0x00007f3ba8205800 nid=0x2f89 waiting for monitor entry [0x00007f3b6a361000]
   java.lang.Thread.State: BLOCKED (on object monitor)
    at org.mortbay.log.StdErrLog.warn(StdErrLog.java:128)
    - waiting to lock <0x0000000087b405c8> (a java.lang.StringBuffer)
    at org.mortbay.jetty.handler.ContextHandler$SContext.log(ContextHandler.java:1424)
    at com.google.gwt.user.server.rpc.RPCServletUtils.writeResponseForUnexpectedFailure(RPCServletUtils.java:389)
    at com.google.gwt.user.server.rpc.AbstractRemoteServiceServlet.doUnexpectedFailure(AbstractRemoteServiceServlet.java:110)
    at com.google.gwt.user.server.rpc.AbstractRemoteServiceServlet.doPost(AbstractRemoteServiceServlet.java:67)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)
    at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
    at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:401)
    at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
    at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
    at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:766)
    at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:450)
    at org.mortbay.jetty.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:230)
    at org.mortbay.jetty.handler.HandlerCollection.handle(HandlerCollection.java:114)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.Server.handle(Server.java:326)
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
    at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:945)
    at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:756)
    at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
    at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:410)
    at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)

   Locked ownable synchronizers:
    - None

...etc...

这是一个问题吗？这可能是什么原因造成的？该应用程序正在开发机器上运行，我是唯一一个查看它的人。

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1 回答 1

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简短回答：您的应用程序发生了一些内部异常，您需要检查服务器日志（码头日志、访问日志、应用程序日志等）以确定根本原因。

分析：

被StringBuffer定义为实例变量org.mortbay.log.StdErrLog：

public class StdErrLog implements Logger {    
  // ...
  StringBuffer _buffer = new StringBuffer();
  //...
}

它的使用被包装在一个synchronized块中：

public void warn(String msg,Object arg0, Object arg1)
{
    String d=_dateCache.now();
    int ms=_dateCache.lastMs();
    synchronized(_buffer)
    {
        tag(d,ms,":WARN:");
        format(msg,arg0,arg1);
        System.err.println(_buffer.toString());
    }
}

因此，如果有多个线程试图调用此方法，则只有一个线程会通过，其他线程将不得不等待（如在您的线程堆栈中）。

我们可以看到这个方法是从 调用的com.google.gwt.user.server.rpc.AbstractRemoteServiceServlet.doUnexpectedFailure()，这意味着你的内部代码中有一个内部异常。以下是从该方法的 JavaDoc中引用的：

此方法仅针对不属于服务方法签名的异常或错误，或者由 SecurityExceptions、SerializationExceptions 或 RPC 框架内的其他故障导致的异常或错误调用。

由于此方法有太多线程阻塞，并且您是唯一访问服务器的客户端，我猜您的客户端代码中可能存在错误，它会向服务器发送一堆意外请求。您需要检查服务器日志（码头日志、访问日志、应用程序日志等）以确定根本原因。

于 2013-02-27T05:30:14.453 回答