java 線程池 ThreadPoolExecutor

java 線程池 ThreadPoolExecutor

使用線程池的好處：

• 降低資源消耗
• 提高響應速度
• 提高線程的可管理性

ThreadPoolExecutor executor = new ThreadPoolExecutor(
                CORE_POOL_SIZE,
                MAX_POOL_SIZE,
                KEEP_ALIVE_TIME,
                TimeUnit.SECONDS,
                new ArrayBlockingQueue<>(100),
                new ThreadPoolExecutor.CallerRunsPolicy());

1. CORE_POOL_SIZE：核心線程數

2. MAX_POOL_SIZE：最大線程數

3. KEEP_ALIVE_TIME：等待時間

4. TimeUnit.SECONDS：等待時間的單位

5. new ArrayBlockingQueue<>(QUEUE_CAPACITY)：任務隊列爲 ArrayBlockingQueue ，容量爲 100

6. new ThreadPoolExecutor.CallerRunsPolicy()：飽和策略爲 CallerRunsPolicy

   ①：ThreadPoolExecutor.AbortPolicy：拋出 RejectedExecutionException來拒絕新任務的處理。
   ②：ThreadPoolExecutor.CallerRunsPolicy：調用並執行自己的線程以運行任務，即直接在調用execute方法的線程中運行（run）被拒絕的任務。如果執行程序已關閉，則替換任務。
   ③：ThreadPoolExecutor.DiscardPolicy：不處理新任務，直接丟棄掉。
   ④：ThreadPoolExecutor.DiscardOldestPolicy： 丟棄最早的未處理的任務請求。

ThreadPoolExecutor提供了幾種方法，通過它們我們可以找到執行程序的當前狀態，池大小，活動線程數和任務數。

public class MyRunnable implements Runnable {

    private ThreadPoolExecutor executor;
    private int seconds;

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

    @Override
    public void run()
    {
            System.out.println(
                    String.format("[monitor] [%d/%d] Active: %d, Completed: %d, Task: %d, isShutdown: %s, isTerminated: %s, Thread:%d",
                            this.executor.getPoolSize(),
                            this.executor.getCorePoolSize(),
                            this.executor.getActiveCount(),
                            this.executor.getCompletedTaskCount(),
                            this.executor.getTaskCount(),
                            this.executor.isShutdown(),
                            this.executor.isTerminated(),
                            this.seconds
                    ));
            try {
                Thread.sleep(5000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

    }
}

這是使用ThreadPoolExecutor實現線程池的示例。

public class Test {

    private static final int CORE_POOL_SIZE = 5;
    private static final int MAX_POOL_SIZE = 10;
    private static final int QUEUE_CAPACITY = 100;
    private static final int KEEP_ALIVE_TIME = 10;
    public static void main(String args[]){

        ThreadPoolExecutor executorPool = new ThreadPoolExecutor(
                CORE_POOL_SIZE,
                MAX_POOL_SIZE,
                KEEP_ALIVE_TIME,
                TimeUnit.SECONDS,
                new ArrayBlockingQueue<>(QUEUE_CAPACITY),
                new ThreadPoolExecutor.CallerRunsPolicy()
        );
        //將工作提交到線程池
        for(int i=0; i<10; i++){
            executorPool.execute(new MyRunnable(executorPool, i));
        }
        //終止線程池
        executorPool.shutdown();
        while (!executorPool.isTerminated()) {
        }
        System.out.println("finish！");

    }

}

這是上面演示的輸出。

[monitor] [4/5] Active: 5, Completed: 0, Task: 10, isShutdown: true, isTerminated: false, Thread:0
[monitor] [5/5] Active: 5, Completed: 0, Task: 10, isShutdown: true, isTerminated: false, Thread:1
[monitor] [5/5] Active: 5, Completed: 0, Task: 10, isShutdown: true, isTerminated: false, Thread:4
[monitor] [5/5] Active: 5, Completed: 0, Task: 10, isShutdown: true, isTerminated: false, Thread:3
[monitor] [5/5] Active: 5, Completed: 0, Task: 10, isShutdown: true, isTerminated: false, Thread:2
[monitor] [5/5] Active: 4, Completed: 3, Task: 10, isShutdown: true, isTerminated: false, Thread:6
[monitor] [5/5] Active: 5, Completed: 3, Task: 10, isShutdown: true, isTerminated: false, Thread:7
[monitor] [5/5] Active: 3, Completed: 3, Task: 10, isShutdown: true, isTerminated: false, Thread:5
[monitor] [5/5] Active: 4, Completed: 5, Task: 9, isShutdown: true, isTerminated: false, Thread:8
[monitor] [5/5] Active: 5, Completed: 5, Task: 10, isShutdown: true, isTerminated: false, Thread:9
finish！