从头认识java-18.2 基本的线程机制（2）-Executors的使用

在前面的章节我们都是直接对Thread进行管理，我们这里解释一下另一个管理Thread的类Executors。

1.例子：

package com.ray.ch17;import java.util.concurrent.CountDownLatch;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;public class Test {public static void main(String[] args) throws InterruptedException {long startTime = System.currentTimeMillis();ExecutorService executorService = Executors.newCachedThreadPool();CountDownLatch countDownLatch = new CountDownLatch(5);for (int i = 5; i < 10; i++) {DoneMission doneMission = new DoneMission(i, countDownLatch);executorService.execute(doneMission);}executorService.shutdown();countDownLatch.await();long endTime = System.currentTimeMillis();System.out.println();System.out.println(endTime - startTime);}}class DoneMission implements Runnable {private final int id = index++;private int count = 0;private static int index = 0;private CountDownLatch countDownLatch;public DoneMission(int count, CountDownLatch countDownLatch) {this.count = count;this.countDownLatch = countDownLatch;}public String leftMission() {return "#" + id + "(" + count + ") ";}@Overridepublic void run() {while (count-- > 0) {System.out.print(leftMission());try {Thread.sleep(100);} catch (InterruptedException e) {e.printStackTrace();}Thread.yield();}countDownLatch.countDown();}}

解释：

（1）运行任务的类跟前面的基本一致

（2）使用Executors.newCachedThreadPool()生成线程池，当需要线程驱动的时候，我们可以到里面拿，它生成的线程数是有系统控制的。

2.对线程的数量做出控制

package com.ray.ch17;import java.util.concurrent.CountDownLatch;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;public class Test {public static void main(String[] args) throws InterruptedException {long startTime = System.currentTimeMillis();ExecutorService executorService = Executors.newFixedThreadPool(5);//控制线程的数量CountDownLatch countDownLatch = new CountDownLatch(5);for (int i = 5; i < 10; i++) {DoneMission doneMission = new DoneMission(i, countDownLatch);executorService.execute(doneMission);}executorService.shutdown();countDownLatch.await();long endTime = System.currentTimeMillis();System.out.println();System.out.println(endTime - startTime);}}class DoneMission implements Runnable {private final int id = index++;private int count = 0;private static int index = 0;private CountDownLatch countDownLatch;public DoneMission(int count, CountDownLatch countDownLatch) {this.count = count;this.countDownLatch = countDownLatch;}public String leftMission() {return "#" + id + "(" + count + ") ";}@Overridepublic void run() {while (count-- > 0) {System.out.print(leftMission());try {Thread.sleep(100);} catch (InterruptedException e) {e.printStackTrace();}Thread.yield();}countDownLatch.countDown();}}

上面的代码只是替换了一句，就可以控制线程的数量，但是我们一般还是建议使用cache的那个，因为它对线程池做出来优化。特别是对于短的异步任务它具有明显优势。

3.测试不同线程运行的时间：

package com.ray.ch17;import java.util.concurrent.CountDownLatch;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;public class Test {public static void main(String[] args) throws InterruptedException {long startTime = System.currentTimeMillis();ExecutorService executorService = Executors.newCachedThreadPool();CountDownLatch countDownLatch = new CountDownLatch(5);for (int i = 5; i < 10; i++) {DoneMission doneMission = new DoneMission(i, countDownLatch);executorService.execute(doneMission);}executorService.shutdown();countDownLatch.await();long endTime = System.currentTimeMillis();System.out.println();System.out.println("time:"+(endTime - startTime));}}class DoneMission implements Runnable {private final int id = index++;private int count = 0;private static int index = 0;private CountDownLatch countDownLatch;public DoneMission(int count, CountDownLatch countDownLatch) {this.count = count;this.countDownLatch = countDownLatch;}public String leftMission() {return "#" + id + "(" + count + ") ";}@Overridepublic void run() {while (count-- > 0) {System.out.print(leftMission());try {Thread.sleep(100);} catch (InterruptedException e) {e.printStackTrace();}Thread.yield();}countDownLatch.countDown();}}

输出：

#0(4) #1(5) #2(6) #3(7) #4(8) #0(3) #1(4) #4(7) #3(6) #2(5) #0(2) #1(3) #3(5) #2(4) #4(6) #0(1) #1(2) #4(5) #3(4) #2(3) #0(0) #1(1) #2(2) #4(4) #3(3) #1(0) #2(1) #3(2) #4(3) #4(2) #3(1) #2(0) #3(0) #4(1) #4(0) 
904

控制为3个线程：

package com.ray.ch17;import java.util.concurrent.CountDownLatch;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;public class Test {public static void main(String[] args) throws InterruptedException {long startTime = System.currentTimeMillis();ExecutorService executorService = Executors.newFixedThreadPool(3);CountDownLatch countDownLatch = new CountDownLatch(5);for (int i = 5; i < 10; i++) {DoneMission doneMission = new DoneMission(i, countDownLatch);executorService.execute(doneMission);}executorService.shutdown();countDownLatch.await();long endTime = System.currentTimeMillis();System.out.println();System.out.println(endTime - startTime);}}class DoneMission implements Runnable {private final int id = index++;private int count = 0;private static int index = 0;private CountDownLatch countDownLatch;public DoneMission(int count, CountDownLatch countDownLatch) {this.count = count;this.countDownLatch = countDownLatch;}public String leftMission() {return "#" + id + "(" + count + ") ";}@Overridepublic void run() {while (count-- > 0) {System.out.print(leftMission());try {Thread.sleep(100);} catch (InterruptedException e) {e.printStackTrace();}Thread.yield();}countDownLatch.countDown();}}

输出：

#0(4) #2(6) #1(5) #1(4) #0(3) #2(5) #0(2) #2(4) #1(3) #1(2) #2(3) #0(1) #0(0) #1(1) #2(2) #1(0) #2(1) #3(7) #3(6) #4(8) #2(0) #3(5) #4(7) #3(4) #4(6) #3(3) #4(5) #4(4) #3(2) #4(3) #3(1) #4(2) #3(0) #4(1) #4(0) 
1504

控制为单线程：

package com.ray.ch17;import java.util.concurrent.CountDownLatch;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;public class Test {public static void main(String[] args) throws InterruptedException {long startTime = System.currentTimeMillis();ExecutorService executorService = Executors.newSingleThreadExecutor();CountDownLatch countDownLatch = new CountDownLatch(5);for (int i = 5; i < 10; i++) {DoneMission doneMission = new DoneMission(i, countDownLatch);executorService.execute(doneMission);}executorService.shutdown();countDownLatch.await();long endTime = System.currentTimeMillis();System.out.println();System.out.println(endTime - startTime);}}class DoneMission implements Runnable {private final int id = index++;private int count = 0;private static int index = 0;private CountDownLatch countDownLatch;public DoneMission(int count, CountDownLatch countDownLatch) {this.count = count;this.countDownLatch = countDownLatch;}public String leftMission() {return "#" + id + "(" + count + ") ";}@Overridepublic void run() {while (count-- > 0) {System.out.print(leftMission());try {Thread.sleep(100);} catch (InterruptedException e) {e.printStackTrace();}Thread.yield();}countDownLatch.countDown();}}

输出：

#0(4) #0(3) #0(2) #0(1) #0(0) #1(5) #1(4) #1(3) #1(2) #1(1) #1(0) #2(6) #2(5) #2(4) #2(3) #2(2) #2(1) #2(0) #3(7) #3(6) #3(5) #3(4) #3(3) #3(2) #3(1) #3(0) #4(8) #4(7) #4(6) #4(5) #4(4) #4(3) #4(2) #4(1) #4(0) 
3503

单线程说白了就像直接在main方法里面使用for来运行的一样。

4.关于shutdown（）（下面的这段话摘自http://my.oschina.net/bairrfhoinn/blog/177639，笔者觉得他解释的已经比较清楚，其实关键是笔者比较懒，不喜欢打字）

为了关闭在 ExecutorService 中的线程，你需要调用 shutdown() 方法。ExecutorService 并不会马上关闭，而是不再接收新的任务，一旦所有的线程结束执行当前任务，ExecutorServie 才会真的关闭。所有在调用 shutdown() 方法之前提交到 ExecutorService 的任务都会执行。 
如果你希望立即关闭 ExecutorService，你可以调用 shutdownNow() 方法。这个方法会尝试马上关闭所有正在执行的任务，并且跳过所有已经提交但是还没有运行的任务。但是对于正在执行的任务，是否能够成功关闭它是无法保证的，有可能他们真的被关闭掉了，也有可能它会一直执行到任务结束。

总结：这一章节主要介绍Executors的使用。

这一章节就到这里，谢谢。

-----------------------------------

目录