(CSDN迁移) JAVA多线程实现-可控最大并发数线程池(newFixedThreadPool)

上篇文章中介绍了单线程化线程池newSingleThreadExecutor，可控最大并发数线程池(newFixedThreadPool)与其最大的区别是可以通知执行多个线程，可以简单的将newSingleThreadExecutor理解为newFixedThreadPool(1)。例如运行一下两个程序：

单线程化线程池（newSingleThreadExecutor）示例：

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class ThreadPoolByNewSingleThreadExecutor {

    public static void main(String[] args) {
        /**
         * 单线程化的线程池
         */
        ExecutorService singleThreadExecutor = Executors.newSingleThreadExecutor();
        for (int i = 0; i < 10; i++) {
            final int index = i;
            singleThreadExecutor.execute(new Runnable() {
                @Override
                public void run() {
                    Thread.currentThread().setName("Thread i = " + index);
                    System.out.println(Thread.currentThread().getName() + " index = " + index);
                    try {
                        Thread.sleep(500);
                    } catch (InterruptedException e) {
                        System.out.println("exception");
                    }
                }
            });
        }
        singleThreadExecutor.shutdown();
        System.out.println("on the main thread...");
        
    }

}

可控最大并发数线程池（newFixedThreadPool）示例：

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class ThreadPoolByNewFixedThreadPool {
    public static void main(String[] args) {
        
        ExecutorService newFixedThreadPool = Executors.newFixedThreadPool(3);
        for (int i = 0; i < 10; i++) {
            final int index = i;
            newFixedThreadPool.execute(new Runnable() {
                @Override
                public void run() {
                    Thread.currentThread().setName("Thread i = " + index);
                    System.out.println(Thread.currentThread().getName() + " index = " + index);
                    try {
                        Thread.sleep(500);
                    } catch (InterruptedException e) {
                        System.out.println("exception");
                    }
                }
            });
        }
        newFixedThreadPool.shutdown();
        System.out.println("on the main thread...");
    }

}

结果从显示上看虽然很相似，但是观察到的执行效果确实完全不一致的，newSingleThreadPool中，只有一个线程，每次输出一行后暂停0.5秒，newFixedThreadPool(3)中可以创建3个线程，一次输出3行后暂停0.5秒（当然是这三个线程都暂停0.5秒）。

动画对比如下所示：