Java Thread Pool

Logdown -> http://villebez.logdown.com/posts/2014/10/16/238021

這篇主要還是延續前篇 JAVA POP3 Server 實作，改善效能問題。

其實我的問題就如同 Gossip@Openhome 的 Design Pattern: Thread Pool 模式 教學說明的第一段，如下：
「在 Thread-Per-Message 模式 中，每次請求來到，就建立一個新的執行緒，用完就不再使用，然後執行緒的建立需要系統資源，對於一個接受許多請求的情況，不斷的建立新執行緒，會導致系統 效能的降低。」

有興趣看 Thread Pool 的演進，可以看看以下這三個 Design Pattern

1. Thread-Per-Message 模式
2. Worker Thread 模式
3. Thread Pool 模式

但是這裡我沒有要實作 Thread Pool 模式，我只是要了解原理跟用途就好，因為 JavaSE 5.0 以後，已經有 util 可以直接達到 Thread Pool的效果了，也就是 concurrent util。

所以為了這個效能問題呢，將程式改寫，並加上 Monitor Thread 程式來監看 Thread Pool 使用情形。

---

不廢話，直接看程式，其他自己看 java api

...

    public void run() {
        // creating the ThreadPoolExecutor

        ThreadPoolExecutor executorPool = new ThreadPoolExecutor(50, 300, 10,
                TimeUnit.SECONDS, new ArrayBlockingQueue<Runnable>(30),
                Executors.defaultThreadFactory());
        // start the monitoring thread

        MonitorThread monitor = new MonitorThread(executorPool, 5);
        Thread monitorThread = new Thread(monitor);
        monitorThread.start();

        try {
            while (keeprunning) {
                Socket clientSocket = listenSocket.accept();
                clientSocket.setSoTimeout(10000);
                clientSocket.setTcpNoDelay(true);
                executorPool.execute(new manageconnection(clientSocket));
            }
        } catch (IOException excpt) {
            log.error("Sorry ,Failed I/O:" + excpt);
        }
    }

...

---

MonitorThread.java

public class MonitorThread implements Runnable {
    private static final Logger log = Logger.getLogger(MonitorThread.class);
    private ThreadPoolExecutor executor;

    private int seconds;

    private boolean run = true;
    
    public void shutdown() {
        this.run = false;
    }

    public MonitorThread(ThreadPoolExecutor executor, int delay) {
        this.executor = executor;
        this.seconds = delay;
    }

    @Override
    public void run() {
        while (run) {
            log.info(String
                    .format("[monitor] [%d/%d] Active: %d, Completed: %d, Task: %d, isShutdown: %s, isTerminated: %s",
                            this.executor.getPoolSize(),
                            this.executor.getCorePoolSize(),
                            this.executor.getActiveCount(),
                            this.executor.getCompletedTaskCount(),
                            this.executor.getTaskCount(),
                            this.executor.isShutdown(),
                            this.executor.isTerminated()));
            try {
                Thread.sleep(seconds * 1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

    }
}

output
[monitor] [50/50] Active: 1, Completed: 3, Task: 4, isShutdown: false, isTerminated: false

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參考資料：
Java Thread Pool Example using Executors and ThreadPoolExecutor
ThreadPoolExecutor
Interface Executor