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：