JAVA线程池线程复用机制核心摘要

张少飞2024-08-17 21:03

1、线程创建时机

1.1、submitTask

executor.submit(task);

java 复制代码

ExecutorService executor = Executors.newFixedThreadPool(3);

// 创建一个 Callable 任务
 Callable<Integer> task = new Callable<Integer>() {
    @Override
    public Integer call() throws Exception {
       System.out.println("Task is being processed by " + Thread.currentThread().getName());
       Thread.sleep(1000); // 模拟一些工作
       return 42; // 返回结果
            }
};

Future<Integer> future = executor.submit(task);

1.2、addWorker

java 复制代码

        int c = ctl.get();
        if (workerCountOf(c) < corePoolSize) {
            if (addWorker(command, true))
                return;
            c = ctl.get();
        }

1.3、创建线程&跟worker绑定

java 复制代码

        Worker(Runnable firstTask) {
            setState(-1); // inhibit interrupts until runWorker
            this.firstTask = firstTask;
            this.thread = getThreadFactory().newThread(this);
        }

this.thread = getThreadFactory().newThread(this);

这里是worker跟线程关联的核心,new Thread 的时候把woker作为runable传进去了，后面thread.start()的时候，会回调worker的run()方法，这样线程就跟worker绑定了。

java 复制代码

 if (workerAdded) {
                    t.start();
                    workerStarted = true;
                }

启动线程，回调worker 的 runWorker方法

1.4、线程复用核心

java 复制代码

final void runWorker(Worker w) {
        Thread wt = Thread.currentThread();
        Runnable task = w.firstTask;
        w.firstTask = null;
        w.unlock(); // allow interrupts
        boolean completedAbruptly = true;
        try {
            while (task != null || (task = getTask()) != null) {
                w.lock();

while循环，有任务执行，无任务则block，等待任务，这样线程就能做复用了。