tomcat如何利用多线程实现同时处理多个请求-简化版

tomcat如何利用多线程实现同时处理多个请求-简化版

说明

以下内容以《how tomcat works》第四章为原型

整体流程,交互过程以及源码可参考https://blog.csdn.net/qq_29025955/article/details/120196616

启动应用时就创建多个处理实例(线程)

在应用启动时就会去创建多个HttpProcessors实例,然后启动该实例的run()方法,即是创建了多个线程并且让每个线程都处理wait状态。

创建实例:

 /**
     * Create and return a new processor suitable for processing HTTP
     * requests and returning the corresponding responses.
     */
    private HttpProcessor newProcessor() {

        //        if (debug >= 2)
        //            log("newProcessor: Creating new processor");
        HttpProcessor processor = new HttpProcessor(this, curProcessors++);
        if (processor instanceof Lifecycle) {
            try {
                ((Lifecycle) processor).start();
            } catch (LifecycleException e) {
                log("newProcessor", e);
                return (null);
            }
        }
        created.addElement(processor);
        return (processor);

    }

执行run()方法,每个实例都执行自己的run方法(即是针对每个实例都启动一个线程):

 /**
     * The background thread that listens for incoming TCP/IP connections and
     * hands them off to an appropriate processor.
     */
    public void run() {

        // Process requests until we receive a shutdown signal
        while (!stopped) {

            // Wait for the next socket to be assigned
            Socket socket = await();
System.out.println(Thread.currentThread().getName()+": i am awake!");
            if (socket == null)
                continue;

            // Process the request from this socket
            try {
                process(socket);
            } catch (Throwable t) {
                log("process.invoke", t);
            }

            // Finish up this request
            connector.recycle(this);

        }

        // Tell threadStop() we have shut ourselves down successfully
        synchronized (threadSync) {
            threadSync.notifyAll();
        }

    }

上面代码片段中的 await()方法如下表明每个实例对应的线程初始化时都处于wait状态

/**
     * Await a newly assigned Socket from our Connector, or <code>null</code>
     * if we are supposed to shut down.
     */
    private synchronized Socket await() {

        // Wait for the Connector to provide a new Socket
        while (!available) {
            try {
                wait();
            } catch (InterruptedException e) {
            }
        }

        // Notify the Connector that we have received this Socket
        Socket socket = this.socket;
        available = false;
        notifyAll();

        if ((debug >= 1) && (socket != null))
            log("  The incoming request has been awaited");

        return (socket);

    }

客户端发送请求

HttpConnector实例用于监听客户端请求,当请求到来时会将请求指派给一个具体的HttpProcessor实例进行处理,指派完成后会马上返回继续监听客户端请求,同时被指派的HttpProcessor会对请求进行处理,与HttpConnector实例相互独立运行,互不影响。
当第2个、第3个…请求到来时,HttpConnector同样会指派第2个,第3个HttpProcessor实例进行处理,这1 2 3.。。。个HttpProcessor实例(线程)可以同时独立的运行。

HttpConnector的run()方法用于监听客户端请求,同时指派HttpProcessor实例对请求进行处理。

/**
     * The background thread that listens for incoming TCP/IP connections and
     * hands them off to an appropriate processor.
     */
    public void run() {
        // Loop until we receive a shutdown command
        while (!stopped) {
            // Accept the next incoming connection from the server socket
            Socket socket = null;
            try {
                //                if (debug >= 3)
                //                    log("run: Waiting on serverSocket.accept()");
                socket = serverSocket.accept();
                //                if (debug >= 3)
                //                    log("run: Returned from serverSocket.accept()");
                if (connectionTimeout > 0)
                    socket.setSoTimeout(connectionTimeout);
                socket.setTcpNoDelay(tcpNoDelay);
            } catch (AccessControlException ace) {
                log("socket accept security exception", ace);
                continue;
            } catch (IOException e) {
                //                if (debug >= 3)
                //                    log("run: Accept returned IOException", e);
                try {
                    // If reopening fails, exit
                    synchronized (threadSync) {
                        if (started && !stopped)
                            log("accept error: ", e);
                        if (!stopped) {
                            //                    if (debug >= 3)
                            //                        log("run: Closing server socket");
                            serverSocket.close();
                            //                        if (debug >= 3)
                            //                            log("run: Reopening server socket");
                            serverSocket = open();
                        }
                    }
                    //                    if (debug >= 3)
                    //                        log("run: IOException processing completed");
                } catch (IOException ioe) {
                    log("socket reopen, io problem: ", ioe);
                    break;
                } catch (KeyStoreException kse) {
                    log("socket reopen, keystore problem: ", kse);
                    break;
                } catch (NoSuchAlgorithmException nsae) {
                    log("socket reopen, keystore algorithm problem: ", nsae);
                    break;
                } catch (CertificateException ce) {
                    log("socket reopen, certificate problem: ", ce);
                    break;
                } catch (UnrecoverableKeyException uke) {
                    log("socket reopen, unrecoverable key: ", uke);
                    break;
                } catch (KeyManagementException kme) {
                    log("socket reopen, key management problem: ", kme);
                    break;
                }

                continue;
            }

            // Hand this socket off to an appropriate processor
            HttpProcessor processor = createProcessor();
            if (processor == null) {
                try {
                    log(sm.getString("httpConnector.noProcessor"));
                    socket.close();
                } catch (IOException e) {
                    ;
                }
                continue;
            }
            //            if (debug >= 3)
            //                log("run: Assigning socket to processor " + processor);
            processor.assign(socket);

            // The processor will recycle itself when it finishes

        }

        // Notify the threadStop() method that we have shut ourselves down
        //        if (debug >= 3)
        //            log("run: Notifying threadStop() that we have shut down");
        synchronized (threadSync) {
            threadSync.notifyAll();
        }

    }

指派方法 processor.assign(socket)会唤醒在该HttpProcessor实例processor上等待的线程。notifyAll()来实现参考:java多线程之wait()/notify/notifyAll()

  /**
     * Process an incoming TCP/IP connection on the specified socket.  Any
     * exception that occurs during processing must be logged and swallowed.
     * <b>NOTE</b>:  This method is called from our Connector's thread.  We
     * must assign it to our own thread so that multiple simultaneous
     * requests can be handled.
     *
     * @param socket TCP socket to process
     */
    synchronized void assign(Socket socket) {

        // Wait for the Processor to get the previous Socket
        while (available) {
            try {
                wait();
            } catch (InterruptedException e) {
            }
        }

        // Store the newly available Socket and notify our thread
        this.socket = socket;
        available = true;
        notifyAll();

        if ((debug >= 1) && (socket != null))
            log(" An incoming request is being assigned");

    }
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