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[Java教程]proxool 连接池警告分析:appears to have started a thread named [HouseKeeper] but has failed to stop it

1. 问题:日志中出现下面的警告:

 

警告: The web application [ROOT] appears to have started a thread named [HouseKeeper] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
java.lang.Thread.sleep(Native Method)
org.logicalcobwebs.proxool.HouseKeeperThread.run(HouseKeeperThread.java:46)

 

2. 原因调查:

使用的是 proxool 连接池,查看源码,分析如下:

在项目某种情况下,ProxoolFacade.shutdown(); 被调用,他会调用:

  protected static void shutdown(String finalizer, int delay) {    ConnectionPool[] cps = ConnectionPoolManager.getInstance().getConnectionPools();    for (int i = 0; i < cps.length; i++) {      removeConnectionPool(finalizer, cps[i], delay);    }    // If a shutdown hook was registered then remove it    try {      if (shutdownHook != null) {        ShutdownHook.remove(shutdownHook);      }    } catch (Throwable t) {      if (LOG.isDebugEnabled()) {        LOG.debug("Unanticipated error during removal of ShutdownHook. Ignoring it.", t);      }    }    // Stop threads    PrototyperController.shutdown();    HouseKeeperController.shutdown();  }

这里 首先 关闭连接池,然后在最后面关闭了一个 housekeeper 的 demaon线程:

 HouseKeeperController.shutdown();
  /**   * Stop all house keeper threads.   */  protected static void shutdown() {    synchronized(LOCK) {      Iterator i = houseKeeperThreads.iterator();      while (i.hasNext()) {        HouseKeeperThread hkt = (HouseKeeperThread) i.next();        LOG.info("Stopping " + hkt.getName() + " thread");        hkt.cancel();      }      houseKeeperThreads.clear();    }  }

对每一个 housekeeper 线程调用 cancel() 方法,一般只有一个 housekeeper线程:

hkt.cancel();
public class HouseKeeperThread extends Thread {  private static final Log LOG = LogFactory.getLog(HouseKeeperThread.class);  private boolean stop;  public HouseKeeperThread(String name) {    setDaemon(true);    setName(name);  }  public void run() {    while (!stop) {      HouseKeeper hk = HouseKeeperController.getHouseKeeperToRun();      while (hk != null && !stop) {        try {//          if (LOG.isDebugEnabled()) {//            LOG.debug("About to sweep " + hk.getAlias());//          }          hk.sweep();        } catch (ProxoolException e) {          LOG.error("Couldn't sweep " + hk.getAlias(), e);        }        hk = HouseKeeperController.getHouseKeeperToRun();      }      try {        Thread.sleep(5000);      } catch (InterruptedException e) {        LOG.error("Interrupted", e);      }    }  }  protected void cancel() {    stop = true;  }}

尼玛 stop 尽然是一个 普通 的 boolean 变量,感觉应该使用 volatile 修饰!

保错的原因是,housekeeper 线程因为每隔5秒执行一次,而系统 想要 stop 它的时候,它正在 sleep ,所以抛出了异常:

警告: The web application [ROOT] appears to have started a thread named [HouseKeeper] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread: java.lang.Thread.sleep(Native Method) org.logicalcobwebs.proxool.HouseKeeperThread.run(HouseKeeperThread.java:46)

但是,因为 设置了 stop = true,所以,当它 sleep 完成之后,也可能会 判断 stop == true, 也可能判断 stop == false,因为这里没有使用 volatile 修饰!

所以最坏的结果,就是 有一个名叫 "HouseKeeper" 的 deamon jvm 线程没有被成功关闭。

 

3. 日志显示,数据库连接池,确实被正确关闭了:

ContainerBackgroundProcessor[StandardEngine[Catalina]] - Proxool shoutdown [INFO ] org.logicalcobwebs.proxool.ConnectionPool.shutdown(ConnectionPool.java:484):ContainerBackgroundProcessor[StandardEngine[Catalina]] - Shutting down 'autumn' pool immediately [ContainerBackgroundProcessor[StandardEngine[Catalina]]] [DEBUG] org.logicalcobwebs.proxool.ConnectionPool.removeProxyConnection(ConnectionPool.java:441):ContainerBackgroundProcessor[StandardEngine[Catalina]] - 000003 (00/05/00) - #0006 removed because of shutdown. [DEBUG] org.logicalcobwebs.proxool.ConnectionPool.shutdown(ConnectionPool.java:547):ContainerBackgroundProcessor[StandardEngine[Catalina]] - Connection #6 closed [DEBUG] org.logicalcobwebs.proxool.ConnectionPool.removeProxyConnection(ConnectionPool.java:441):ContainerBackgroundProcessor[StandardEngine[Catalina]] - 000003 (00/04/00) - #0005 removed because of shutdown. [DEBUG] org.logicalcobwebs.proxool.ConnectionPool.shutdown(ConnectionPool.java:547):ContainerBackgroundProcessor[StandardEngine[Catalina]] - Connection #5 closed [DEBUG] org.logicalcobwebs.proxool.ConnectionPool.removeProxyConnection(ConnectionPool.java:441):ContainerBackgroundProcessor[StandardEngine[Catalina]] - 000003 (00/03/00) - #0004 removed because of shutdown. [DEBUG] org.logicalcobwebs.proxool.ConnectionPool.shutdown(ConnectionPool.java:547):ContainerBackgroundProcessor[StandardEngine[Catalina]] - Connection #4 closed [DEBUG] org.logicalcobwebs.proxool.ConnectionPool.removeProxyConnection(ConnectionPool.java:441):ContainerBackgroundProcessor[StandardEngine[Catalina]] - 000003 (00/02/00) - #0003 removed because of shutdown. [DEBUG] org.logicalcobwebs.proxool.ConnectionPool.shutdown(ConnectionPool.java:547):ContainerBackgroundProcessor[StandardEngine[Catalina]] - Connection #3 closed [DEBUG] org.logicalcobwebs.proxool.ConnectionPool.removeProxyConnection(ConnectionPool.java:441):ContainerBackgroundProcessor[StandardEngine[Catalina]] - 000003 (00/01/00) - #0002 removed because of shutdown. [DEBUG] org.logicalcobwebs.proxool.ConnectionPool.shutdown(ConnectionPool.java:547):ContainerBackgroundProcessor[StandardEngine[Catalina]] - Connection #2 closed [DEBUG] org.logicalcobwebs.proxool.ConnectionPool.removeProxyConnection(ConnectionPool.java:441):ContainerBackgroundProcessor[StandardEngine[Catalina]] - 000003 (00/00/00) - #0001 removed because of shutdown. [DEBUG] org.logicalcobwebs.proxool.ConnectionPool.shutdown(ConnectionPool.java:547):ContainerBackgroundProcessor[StandardEngine[Catalina]] - Connection #1 closed [INFO ] org.logicalcobwebs.proxool.ConnectionPool.shutdown(ConnectionPool.java:564):ContainerBackgroundProcessor[StandardEngine[Catalina]] - 'autumn' pool has been closed down by ContainerBackgroundProcessor[StandardEngine[Catalina]] in 6 milliseconds. [DEBUG] org.logicalcobwebs.proxool.ShutdownHook.remove(ShutdownHook.java:41):ContainerBackgroundProcessor[StandardEngine[Catalina]] - Removed shutdownHook [INFO ] org.logicalcobwebs.proxool.PrototyperController.shutdown(PrototyperController.java:100):ContainerBackgroundProcessor[StandardEngine[Catalina]] - Stopping Prototyper thread [INFO ] org.logicalcobwebs.proxool.HouseKeeperController.shutdown(HouseKeeperController.java:107):ContainerBackgroundProcessor[StandardEngine[Catalina]] - Stopping HouseKeeper thread 

排除了 poxool 导致 数据库连接泄露的问题。