Tomcat的Session过期处理策略

tomcat容器实现类都继承了ContainerBase类,容器在启动的时候都会调用ContainerBase类的threadStart()方法,threadStart()方法如下:

 

 protected void threadStart() {

     if (thread != null)
         return;
     if (backgroundProcessorDelay <= 0)
         return;

     threadDone = false;
     String threadName = "ContainerBackgroundProcessor[" + toString() + "]";
     thread = new Thread(new ContainerBackgroundProcessor(), threadName);
     thread.setDaemon(true);
     thread.start();
 }

 StandardHost,StandardContext,StandardWrapper类的backgroundProcessorDelay的值都为-1,所以ContainerBackgroundProcessor线程都没有启动.而StandardEngine类在创建的时候 将backgroundProcessorDelay 的值设置为10.所以ContainerBackgroundProcessor线程在StandardEngine里启动,ContainerBackgroundProcessor线程代码如下:

 protected class ContainerBackgroundProcessor implements Runnable {

         public void run() {
             while (!threadDone) {
                 try {
                     Thread.sleep(backgroundProcessorDelay * 1000L);
                 } catch (InterruptedException e) {
                     ;
                 }
                 if (!threadDone) {
                     Container parent = (Container) getMappingObject();//得到StandardEngine
                     ClassLoader cl =
                         Thread.currentThread().getContextClassLoader();
                     if (parent.getLoader() != null) {
                         cl = parent.getLoader().getClassLoader();
                     }
                     processChildren(parent, cl);
                 }
             }
         }

         protected void processChildren(Container container, ClassLoader cl) {
             try {
                 if (container.getLoader() != null) {
                     Thread.currentThread().setContextClassLoader
                         (container.getLoader().getClassLoader());
                 }
                 container.backgroundProcess();
             } catch (Throwable t) {
                 log.error("Exception invoking periodic operation: ", t);
             } finally {
                 Thread.currentThread().setContextClassLoader(cl);
             }
             Container[] children = container.findChildren();
             for (int i = 0; i < children.length; i++) {
                 if (children[i].getBackgroundProcessorDelay() <= 0) {
                     processChildren(children[i], cl);
                 }
             }
         }

     }

 ContainerBackgroundProcessor每隔10秒执行一下线程,线程递归调用StandardEngine,StandardHost,StandardContext,StandardWrapper类的backgroundProcess()方法(backgroundProcess()方法在ContainerBase类中)

backgroundProcess()方法如下:

 public void backgroundProcess() {

     if (!started)
         return;

     if (cluster != null) {
         try {
             cluster.backgroundProcess();
         } catch (Exception e) {
             log.warn(sm.getString("containerBase.backgroundProcess.cluster", cluster), e);
         }
     }
     if (loader != null) {
         try {
             loader.backgroundProcess();
         } catch (Exception e) {
             log.warn(sm.getString("containerBase.backgroundProcess.loader", loader), e);
         }
     }
     if (manager != null) {//manager的实现类StandardManager
         try {
             manager.backgroundProcess();
         } catch (Exception e) {
             log.warn(sm.getString("containerBase.backgroundProcess.manager", manager), e);
         }
     }
     if (realm != null) {
         try {
             realm.backgroundProcess();
         } catch (Exception e) {
             log.warn(sm.getString("containerBase.backgroundProcess.realm", realm), e);
         }
     }
     Valve current = pipeline.getFirst();
     while (current != null) {
         try {
             current.backgroundProcess();
         } catch (Exception e) {
             log.warn(sm.getString("containerBase.backgroundProcess.valve", current), e);
         }
         current = current.getNext();
     }
     lifecycle.fireLifecycleEvent(Lifecycle.PERIODIC_EVENT, null);
 }

 

   在调用StandContext类的backgroundProcess()方法时, 会调用StandardManager的backgroundProcess()方法,该方法如下:

       

 public void backgroundProcess() {
     count = (count + 1) % processExpiresFrequency;
     if (count == 0)
         processExpires();
 }

 
 processExpiresFrequency的默认值为6,所以每6*10秒会调一次processExpires()方法,processExpires()方法如下:

  

 public void processExpires() {

     long timeNow = System.currentTimeMillis();
     Session sessions[] = findSessions();
     int expireHere = 0 ;

     if(log.isDebugEnabled())
         log.debug("Start expire sessions " + getName() + " at " + timeNow + " sessioncount " + sessions.length);
     for (int i = 0; i < sessions.length; i++) {
         if (sessions[i]!=null && !sessions[i].isValid()) {//判断session是否有效,无效则清除
             expireHere++;
         }
     }
     long timeEnd = System.currentTimeMillis();
     if(log.isDebugEnabled())
          log.debug("End expire sessions " + getName() + " processingTime " + (timeEnd - timeNow) + " expired sessions: " + expireHere);
     processingTime += ( timeEnd - timeNow );

 }

  该方法主要判断session是否过期,过期则清除.

 

  

    整个过程看起来有点复杂,简单地来说,就是tomcat服务器在启动的时候初始化了一个守护线程,定期6*10秒去检查有没有Session过期.过期则清除.