Tomcat的Session过期处理策略

314598340

　　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.getBackgroundProcessorDelay() <= 0) {
processChildren(children, 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!=null && !sessions.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.