自定义线程池 ThreadPoolExecutor

Executor框架最核心的类是ThreadPoolExecutor，它是线程池的实现类，主要由下列4个组件构成。
·corePool：核心线程池的大小。
·maximumPool：最大线程池的大小。
·BlockingQueue：用来暂时保存任务的工作队列。
·RejectedExecutionHandler：当ThreadPoolExecutor已经关闭或ThreadPoolExecutor已经饱和时（达到了最大线程池大小且工作队列已满），execute()方法将要调用的Handler。
-------------------------------------------------------------------------读书笔记摘自 书名：Java并发编程的艺术 作者：方腾飞；魏鹏；程晓明

线程任务

public class Task implements Runnable {
    private final String name;

    public Task(String name) {
        this.name = name;
    }

    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName() + " → " + name + " Start Time = " + new Date());
        processCommand();
        System.out.println(Thread.currentThread().getName() + " → " + name + " End   Time = " + new Date());
    }

    private void processCommand() {
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

自定义线程池

public class CustomThreadPool {
    public static void main(String[] args) {
        System.out.println(Thread.currentThread().getName() + "线程: Start at: " + new Date());

        // 创建等待队列
        BlockingQueue<Runnable> blockingQueue = new ArrayBlockingQueue<>(20);

        // 创建线程池、池中保存的线程数为3，允许的最大线程数为5
        ThreadPoolExecutor pool = new ThreadPoolExecutor(3, 5, 50, TimeUnit.MILLISECONDS, blockingQueue);

        // 创建七个任务
        // 每个任务会在一个线程上执行
        for (int i = 1; i < 10; i++) {
            System.out.println("添加了第" + i + "个任务类");
            pool.execute(new Task("线程任务" + i));
        }

        // 关闭线程池
        pool.shutdown();

        System.out.println(Thread.currentThread().getName() + "线程: 打卡：" + new Date());

        long i = 0;
        while (!pool.isTerminated()) {
            // wait for all tasks to finish
            i++;
        }

        System.out.println(Thread.currentThread().getName() + "线程: Finished all threads at：" + new Date() + ". isTerminated 判断次数 " + i);
    }
}

---

执行结果分析

执行结果
main线程: Start at: Fri May 19 18:28:52 CST 2023	进入main线程
添加了第1个任务类	构建任务放入线程池
添加了第2个任务类
添加了第3个任务类
添加了第4个任务类
添加了第5个任务类
添加了第6个任务类
添加了第7个任务类
添加了第8个任务类
添加了第9个任务类
添加了第10个任务类
main线程: 打卡：Fri May 19 18:28:52 CST 2023	主线程打个卡
pool-1-thread-2 → 线程任务2 Start Time = Fri May 19 18:28:52 CST 2023	线程池开始分配线程执行线程任务
pool-1-thread-1 → 线程任务1 Start Time = Fri May 19 18:28:52 CST 2023
pool-1-thread-3 → 线程任务3 Start Time = Fri May 19 18:28:52 CST 2023
pool-1-thread-2 → 线程任务2 End Time = Fri May 19 18:28:55 CST 2023
pool-1-thread-2 → 线程任务4 Start Time = Fri May 19 18:28:55 CST 2023
pool-1-thread-3 → 线程任务3 End Time = Fri May 19 18:28:55 CST 2023
pool-1-thread-1 → 线程任务1 End Time = Fri May 19 18:28:55 CST 2023
pool-1-thread-1 → 线程任务6 Start Time = Fri May 19 18:28:55 CST 2023
pool-1-thread-3 → 线程任务5 Start Time = Fri May 19 18:28:55 CST 2023
pool-1-thread-2 → 线程任务4 End Time = Fri May 19 18:28:58 CST 2023
pool-1-thread-2 → 线程任务7 Start Time = Fri May 19 18:28:58 CST 2023
pool-1-thread-3 → 线程任务5 End Time = Fri May 19 18:28:58 CST 2023
pool-1-thread-1 → 线程任务6 End Time = Fri May 19 18:28:58 CST 2023
pool-1-thread-3 → 线程任务8 Start Time = Fri May 19 18:28:58 CST 2023
pool-1-thread-1 → 线程任务9 Start Time = Fri May 19 18:28:58 CST 2023
pool-1-thread-2 → 线程任务7 End Time = Fri May 19 18:29:01 CST 2023
pool-1-thread-2 → 线程任务10 Start Time = Fri May 19 18:29:01 CST 2023
pool-1-thread-3 → 线程任务8 End Time = Fri May 19 18:29:01 CST 2023
pool-1-thread-1 → 线程任务9 End Time = Fri May 19 18:29:01 CST 2023
pool-1-thread-2 → 线程任务10 End Time = Fri May 19 18:29:04 CST 2023
main线程: Finished all threads at：Fri May 19 18:29:04 CST 2023. isTerminated 判断次数 25692088316	所有线程全部执行完毕
从结果中可以看出，10 个任务是在线程池的 3 个线程上执行的