自定义线程池

转自：https://www.cnblogs.com/nele/p/6502750.html

线程池执行的流程：

当任务提交给ThreadPoolExecutor 线程池中，先检查核心线程数是否已经全部使用，

如果没有交由核心线程去执行任务，

如果核心线程数已经全部占用，则将任务添加到队列里面，

如果队列已经占满，比较当前线程池的中线程的数量是不是与超过maximumPoolSize，如果没有查过则创建线程去执行。

也就是说线程池最多可以接受多少任务呢？就是maximumPoolSize+队列的大小。

当线程池中的线程的数量大于corePoolSize数量有空闲线程则执行回收，回收时间是keepAliveTime，单位是unit，都是初始化的时候设置的。

下面通过代码来说明：

定义一个实现了Runnable接口的类，当作任务类：

package com.ctrip.ck.test.thread.pool;

public class MyTask implements Runnable {
    private int taskId;
    private String taskName;

    public MyTask(int taskId, String taskName) {
        this.taskId = taskId;
        this.taskName = taskName;
    }

    //getter/setter
    public int getTaskId() {
        return taskId;
    }
    public void setTaskId(int taskId) {
        this.taskId = taskId;
    }

    public String getTaskName() {
        return taskName;
    }
    public void setTaskName(String taskName) {
        this.taskName = taskName;
    }


    @Override
    public void run() {
        System.out.println("taskId:" + taskId + ",taskName:" + taskName);
        try {
            Thread.sleep(10000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

}

定义如下的线程池：

private static ThreadPoolExecutor pool = new ThreadPoolExecutor(// 自定义一个线程池
        1,      // coreSize
        2,  // maxSize
        60,    // 60s
        TimeUnit.SECONDS,
        new ArrayBlockingQueue<>(3), // 有界队列，容量是3个
        Executors.defaultThreadFactory(),
        new ThreadPoolExecutor.AbortPolicy()
);

测试类：

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

public class PoolTest {
    private static ThreadPoolExecutor pool = new ThreadPoolExecutor(// 自定义一个线程池
            1,      // coreSize
            2,  // maxSize
            60,    // 60s
            TimeUnit.SECONDS,
            new ArrayBlockingQueue<>(3), // 有界队列，容量是3个
            Executors.defaultThreadFactory(),
            new ThreadPoolExecutor.AbortPolicy()
    );

    public static void main(String[] args) {
        pool.execute(new MyTask(1, "任务1"));
        System.out.println("活跃的线程数：" + pool.getActiveCount() + ",核心线程数：" + pool.getCorePoolSize() + ",线程池大小：" + pool.getPoolSize() + ",队列的大小" + pool.getQueue().size());

        pool.execute(new MyTask(2, "任务2"));
        System.out.println("活跃的线程数：" + pool.getActiveCount() + ",核心线程数：" + pool.getCorePoolSize() + ",线程池大小：" + pool.getPoolSize() + ",队列的大小" + pool.getQueue().size());

        pool.execute(new MyTask(3, "任务3"));
        System.out.println("活跃的线程数：" + pool.getActiveCount() + ",核心线程数：" + pool.getCorePoolSize() + ",线程池大小：" + pool.getPoolSize() + ",队列的大小" + pool.getQueue().size());

        pool.execute(new MyTask(4, "任务4"));
        System.out.println("活跃的线程数：" + pool.getActiveCount() + ",核心线程数：" + pool.getCorePoolSize() + ",线程池大小：" + pool.getPoolSize() + ",队列的大小" + pool.getQueue().size());

        pool.execute(new MyTask(5, "任务5"));
        System.out.println("活跃的线程数：" + pool.getActiveCount() + ",核心线程数：" + pool.getCorePoolSize() + ",线程池大小：" + pool.getPoolSize() + ",队列的大小" + pool.getQueue().size());

        pool.execute(new MyTask(6, "任务6"));
        System.out.println("活跃的线程数：" + pool.getActiveCount() + ",核心线程数：" + pool.getCorePoolSize() + ",线程池大小：" + pool.getPoolSize() + ",队列的大小" + pool.getQueue().size());

        pool.shutdown();
        System.out.println("------ over ------");
    }

}

运行结果：

活跃的线程数：1,核心线程数：1,线程池大小：1,队列的大小0
活跃的线程数：1,核心线程数：1,线程池大小：1,队列的大小1
taskId:1,taskName:任务1
活跃的线程数：1,核心线程数：1,线程池大小：1,队列的大小2
活跃的线程数：1,核心线程数：1,线程池大小：1,队列的大小3
活跃的线程数：2,核心线程数：1,线程池大小：2,队列的大小3
Exception in thread "main" taskId:5,taskName:任务5
java.util.concurrent.RejectedExecutionException: Task com.ctrip.ck.test.thread.pool.MyTask@3532ec19 rejected from java.util.concurrent.ThreadPoolExecutor@68c4039c[Running, pool size = 2, active threads = 2, queued tasks = 3, completed tasks = 0]
    at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2047)
    at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:823)
    at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1369)
    at com.ctrip.ck.test.thread.pool.PoolTest.main(PoolTest.java:36)
taskId:2,taskName:任务2
taskId:3,taskName:任务3
taskId:4,taskName:任务4