Java线程池ThreadPoolExecutor的参数含义

1.先看构造方法

public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue,
                              ThreadFactory threadFactory,
                              RejectedExecutionHandler handler) {
        if (corePoolSize < 0 ||
            maximumPoolSize <= 0 ||
            maximumPoolSize < corePoolSize ||
            keepAliveTime < 0)
            throw new IllegalArgumentException();
        if (workQueue == null || threadFactory == null || handler == null)
            throw new NullPointerException();
        this.acc = System.getSecurityManager() == null ?
                null :
                AccessController.getContext();
        this.corePoolSize = corePoolSize;
        this.maximumPoolSize = maximumPoolSize;
        this.workQueue = workQueue;
        this.keepAliveTime = unit.toNanos(keepAliveTime);
        this.threadFactory = threadFactory;
        this.handler = handler;
    }

各个参数的含义：

/**
 * corePoolSize  核心线程池大小
 * maximumPoolSize  最大线程池大小
 * keepAliveTime  线程最大空闲时间
 * unit  时间单位
 * workQueue  线程等待队列
 * threadFactory  线程创建工厂
 * handler  拒绝策略
 */

2.运行机制

当任务加进来之后，先创建核心线程数执行任务；当大于核心线程数时；它会把任务添加到工作队列中，同时开始创建新的线程来执行任务；当总线程数超过最大线程数时；就会交给handler来处理，一般会被拒绝。

3.看一个例子

package com.ysl.rxjava;

import sun.util.calendar.CalendarSystem;

import java.io.IOException;
import java.util.Calendar;
import java.util.Date;
import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicInteger;

public class ThreadPoolTest {

    public static void main(String[] args) throws InterruptedException, IOException {
        int corePoolSize = 2;
        int maximumPoolSize = 3;
        long keepAliveTime = 10;
        TimeUnit unit = TimeUnit.SECONDS;
        BlockingQueue<Runnable> workQueue = new ArrayBlockingQueue<>(2);
        ThreadFactory threadFactory = new NameTreadFactory();
        RejectedExecutionHandler handler = new MyIgnorePolicy();
        /**
         * corePoolSize  核心线程池大小
         * maximumPoolSize  最大线程池大小
         * keepAliveTime  线程最大空闲时间
         * unit  时间单位
         * workQueue  线程等待队列
         * threadFactory  线程创建工厂
         * handler  拒绝策略
         */
        ThreadPoolExecutor executor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, unit,
                workQueue, threadFactory, handler);
        executor.prestartAllCoreThreads(); // 预启动所有核心线程

        Thread.sleep(2000);

        for (int i = 1; i <= 2; i++) {
            MyTask task = new MyTask(String.valueOf(i));
            executor.execute(task);
            System.out.println(i+"，workQueue.size:"+workQueue.size());
        }

        System.in.read(); //阻塞主线程
    }

    static class NameTreadFactory implements ThreadFactory {
        private final AtomicInteger mThreadNum = new AtomicInteger(1);

        @Override
        public Thread newThread(Runnable r) {
            Thread t = new Thread(r, "my-thread-" + mThreadNum.getAndIncrement());
            System.out.println(t.getName() + " has been created");
            return t;
        }
    }

    public static class MyIgnorePolicy implements RejectedExecutionHandler {

        public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
            doLog(r, e);
        }

        private void doLog(Runnable r, ThreadPoolExecutor e) {
            // 可做日志记录等
            System.err.println( r.toString() + " rejected");
//          System.out.println("completedTaskCount: " + e.getCompletedTaskCount());
        }
    }

    static class MyTask implements Runnable {
        private String name;

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

        @Override
        public void run() {
            try {
                System.out.println(this.toString() + " is running!");
                Thread.sleep(10000); //让任务执行慢点
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

        public String getName() {
            return name;
        }

        @Override
        public String toString() {
            return "MyTask [name=" + name + "]";
        }
    }

}

自己创建的线程池；核心线程2；工作队列2；总线程数是3；

当for循环一次和两次时：

核心线程就够用了，不会创建第三个线程了。

当for循环三次或四次时：

核心线程数 + 队列大小刚好可以放下；所以3、4号任务放到了工作队列里；等待执行；当1、2执行完了，开始执行3、4.

当for循环5次时：

可以看到1、2执行了，3、4进入队列了，最后等1、2执行完了才执行；又创建了一个3号线程，并且立马执行了5号任务；

当执行6次及以上：

可以发现，前面和循环5次一样；第六次没有执行而是直接被拒绝了；因为线程数达到了最大数量，而且都在使用；工作队列也是满的；此时就交给handler处理了。handler里面拒绝处理任务。