Executors快速创建线程池以及管理线程池

• Executors快速创建线程以及管理线程池
• 简介
• Executors方法介绍
• • 1. newFixedThreadPool
  • 2. newSingleThreadExecutor
  • 3. newCachedThreadPool
  • 4. newScheduledThreadPool
  • 5. newWorkStealingPool

• Executors类属于java.util.concurrent包；
• 线程池的创建分为两种方式：ThreadPoolExecutor 和 Executors；
• Executors（静态Executor工厂）用于创建线程池；
• 工厂和工具方法Executor ， ExecutorService ， ScheduledExecutorService ， ThreadFactory和Callable在此包中定义的类；

• newFixedThreadPool(int nThreads) 数量固定的线程池
• newSingleThreadExecutor() 单个线程的线程池
• newCachedThreadPool() 创建一个可缓存线程池，如果线程池长度超过处理需要，可灵活回收空闲线程，若无可回收，则新建线程。
• newScheduledThreadPool(int corePoolSize) 周期性任务线程池
• newWorkStealingPool(int parallelism) 多个线程共有一个阻塞队列，而newWorkStealingPool 中每一个线程都有一个自己的队列，当线程发现自己的队列没有任务了，就会到别的线程的队列里获取任务执行。可以简单理解为”窃取“。

• 数量固定的线程池

public class ExecutorsDemo {

    public static void print() {
        System.out.println(Thread.currentThread().getName() + ":执行了");
    }

    public static void main(String[] args) {
        ExecutorService executorService = Executors.newFixedThreadPool(4);
        executorService.execute(() -> ExecutorsDemo.print());
        executorService.execute(() -> ExecutorsDemo.print());
        executorService.execute(() -> ExecutorsDemo.print());
        executorService.execute(() -> ExecutorsDemo.print());
    }
}

• 效果
  

• 单个线程线程池

public class ExecutorsDemo {

    public static void print() {
        System.out.println(Thread.currentThread().getName() + ":执行了");
    }

    public static void main(String[] args) {
        ExecutorService executorService = Executors.newSingleThreadExecutor();
        executorService.execute(() -> ExecutorsDemo.print());
        executorService.execute(() -> ExecutorsDemo.print());
        executorService.execute(() -> ExecutorsDemo.print());
        executorService.execute(() -> ExecutorsDemo.print());
    }
}

• 效果
  

• 可缓存线程池

public class ExecutorsDemo {

    public static void print() {
        System.out.println(Thread.currentThread().getName() + ":执行了");
    }

    public static void main(String[] args) {
        ExecutorService executorService = Executors.newCachedThreadPool();
        executorService.execute(() -> ExecutorsDemo.print());
        executorService.execute(() -> ExecutorsDemo.print());
        executorService.execute(() -> ExecutorsDemo.print());
        executorService.execute(() -> ExecutorsDemo.print());
    }
}

• 效果
  

• 执行定时性或周期性任务线程池
• schedule 延迟任务
• scheduleAtFixedRate 周期性任务，每1秒执行一次，不管当前任务是否结束
• scheduleWithFixedDelay 周期性任务，直到任务停止后新的任务计时才开始

public class ExecutorsDemo {

    public static void print(String msg) {
            System.out.println(Thread.currentThread().getName() + ":" + msg);
    }

    public static void main(String[] args) {
        ScheduledExecutorService scheduled = Executors.newScheduledThreadPool(4);
        // 延迟5秒执行
        scheduled.schedule(() -> ExecutorsDemo.print("延迟任务"), 5000, TimeUnit.MILLISECONDS);
        // 周期性执行，首次延迟5秒，之后每1秒执行一次，不管当前任务是否结束
        scheduled.scheduleAtFixedRate(() -> ExecutorsDemo.print("周期性任务1"), 5000, 1000, TimeUnit.MILLISECONDS);
        // 周期性执行，首次延迟5秒，直到任务停止后新的任务计时才开始，1秒后执行
        scheduled.scheduleWithFixedDelay(() -> ExecutorsDemo.print("周期性任务2"), 5000, 1000, TimeUnit.MILLISECONDS);
    }
}

• 任务窃取线程池

public class ExecutorsDemo {

    public static void print(String msg) {
        System.out.println(Thread.currentThread().getName() + ":" + msg);
    }

    public static void main(String[] args) {
        ExecutorService executorService = Executors.newWorkStealingPool(4);
        executorService.execute(() -> ExecutorsDemo.print("任务1"));
        executorService.execute(() -> ExecutorsDemo.print("任务2"));
        executorService.execute(() -> ExecutorsDemo.print("任务3"));
        executorService.execute(() -> ExecutorsDemo.print("任务4"));
        // 由于线程是抢占式，必须保持程序不终止，否则可能导致线程抢不到任务程序就终止了
        while (true) {}
    }
}

• 效果