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,定期去检查有没有Session过期.过期则清除.