Tomcat源码系列6--Tomcat的Session生成和管理2

starxzj

　　下面谈一谈Session的管理。


一． Session的管理 
当tomcat启动时，会开启一个后台线程，这个后台线程是随容器的启动而启动的,它将定期检查会话超时。
(org.apache.catalina.core.ContainerBase.threadStart()) 

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();
}
　　

1.此时会新建一个ContainerBackgroundProcessor线程。
（org.apache.catalina.core.ContainerBase.ContainerBackgroundProcessor） 

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

2.processChildren(parent,cl)--->processChildren(StandardHost,cl) --->processChildren(StandardContext,cl)，最后StandardContext#backgroundProcess()方法被调用。 

(org.apache.catalina.core.StandardContext.backgroundProcess())
public void backgroundProcess() {
if (!started)
return;
count = (count + 1) % managerChecksFrequency;
if ((getManager() != null) && (count == 0)) {
try {
getManager().backgroundProcess();
} catch ( Exception x ) {
log.warn("Unable to perform background process on manager",x);
}
}
　　


3. StandardManager#processExpires()方法被调用。
org.apache.catalina.session.StandardManager.backgroundProcess() 

public void backgroundProcess() {
processExpires();
}
　　

4. StandardManager#processExpires()被调用，通过调用session#isValid()方法判断session是否有效，如果session无效将被销毁。
（org.apache.catalina.session.StandardManager.processExpires()）
/**
     * 处理所有已失效的session
     */ 
 

   public void processExpires() {
long timeNow = System.currentTimeMillis();
Session sessions[] = findSessions();
for (int i = 0; i < sessions.length; i++) {
StandardSession session = (StandardSession) sessions;
if (!session.isValid()) {
expiredSessions++;
}
}
long timeEnd = System.currentTimeMillis();
processingTime += ( timeEnd - timeNow );
}
　　

5.StandardSession#isValid()最终调用expire(true)，然后返回isValid()的布尔值。
（org.apache.catalina.session.StandardSession.isValid()） 

public boolean isValid() {
if (this.expiring) {
return true;
}
if (!this.isValid ) {
return false;
}
if (accessCount > 0) {
return true;
}
if (maxInactiveInterval >= 0) {
long timeNow = System.currentTimeMillis();
int timeIdle = (int) ((timeNow - thisAccessedTime) / 1000L);
if (timeIdle >= maxInactiveInterval) {
expire(true);※3
}
}
return (this.isValid);
}
　　
※3
StandardSession.expire()方法被调用,session被销毁。
（org.apache.catalina.session.StandardSession.expire(boolean notify)）

public void expire(boolean notify) {
if (expiring)
return;
synchronized (this) {
if (manager == null)
return;
expiring = true;
//唤醒相关的应用程序事件监听者
Context context = (Context) manager.getContainer();
Object listeners[] = context.getApplicationLifecycleListeners();
if (notify && (listeners != null)) {
HttpSessionEvent event =
new HttpSessionEvent(getSession());
for (int i = 0; i < listeners.length; i++) {
int j = (listeners.length - 1) - i;
if (!(listeners[j] instanceof HttpSessionListener))
continue;
HttpSessionListener listener =
(HttpSessionListener) listeners[j];
try {
fireContainerEvent(context,
"beforeSessionDestroyed",
listener);
listener.sessionDestroyed(event);
fireContainerEvent(context,
"afterSessionDestroyed",
listener);
} catch (Throwable t) {
try {
fireContainerEvent(context,
"afterSessionDestroyed",
listener);
} catch (Exception e) {
;
}
manager.getContainer().getLogger().error
(sm.getString("standardSession.sessionEvent"), t);
}
}
}
accessCount = 0;
setValid(false);
// Remove this session from our manager's active sessions
if (manager != null)
manager.remove(this);
//唤醒相关的session事件监听者
if (notify) {
fireSessionEvent(Session.SESSION_DESTROYED_EVENT, null);
}
// 处理完毕后，设置expiring为false
expiring = false;
//解除任何与此相关的session对象的绑定
String keys[] = keys();
for (int i = 0; i < keys.length; i++)
removeAttributeInternal(keys, notify);
}
}