新增线程交叉打印示例代码
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xuwujing
299
src/main/java/com/pancm/question/QuestionTest4.java
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299
src/main/java/com/pancm/question/QuestionTest4.java
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package com.pancm.question;
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import java.util.BitSet;
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import java.util.concurrent.CountDownLatch;
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import java.util.concurrent.Semaphore;
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import java.util.concurrent.atomic.AtomicInteger;
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/**
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* @Title: QuestionTest4
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* @Description: 三个线程，打印ABC
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* @Version:1.0.0
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* @author pancm
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* @date 2018年12月25日
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*/
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public class QuestionTest4 {
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/**
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* @param args
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*/
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public static void main(String[] args) {
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// 只打印一次
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// printOnceLatch();
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System.out.println("");
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// try {
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// printOnceLatch2();
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// } catch (InterruptedException e) {
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// e.printStackTrace();
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// }
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System.out.println("");
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// 十次
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// printTenTimesSemaphore();
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// printTenTimes();
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printTenTimesWaitNotif();
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}
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// 利用jdk1.5的CountDownLatch方法实现
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private static void printOnceLatch() {
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final CountDownLatch countDownLatchForB = new CountDownLatch(1); // 为 B 准备的闭锁，只有该闭锁倒数到 0 ，B 才可以运行
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final CountDownLatch countDownLatchForC = new CountDownLatch(1); // 为 C 准备的闭锁，只有该闭锁倒数到 0 ，C 才可以运行
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final Thread threadA = new Thread() {
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@Override
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public void run() {
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System.out.print("A");
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// B 要在 A 运行完才能运行，就由 A 来倒数
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countDownLatchForB.countDown();
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}
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};
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final Thread threadB = new Thread() {
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@Override
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public void run() {
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try {
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// 等待 A （使用给 B 的闭锁）倒数
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countDownLatchForB.await();
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System.out.print("B");
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} catch (Exception e) {
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e.printStackTrace();
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} finally {
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countDownLatchForC.countDown();
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}
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}
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};
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final Thread threadC = new Thread() {
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@Override
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public void run() {
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try {
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countDownLatchForC.await();
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} catch (Exception e) {
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e.printStackTrace();
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} finally {
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System.out.print("C");
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}
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}
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};
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threadA.start();
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threadB.start();
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threadC.start();
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}
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//利用join来进行
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private static void printOnceLatch2() throws InterruptedException {
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final Thread threadA = new Thread() {
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@Override
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public void run() {
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System.out.print("A");
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}
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};
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final Thread threadB = new Thread() {
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@Override
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public void run() {
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try {
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System.out.print("B");
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} catch (Exception e) {
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e.printStackTrace();
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}
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}
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};
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final Thread threadC = new Thread() {
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@Override
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public void run() {
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try {
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System.out.print("C");
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} catch (Exception e) {
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e.printStackTrace();
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} finally {
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}
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}
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};
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threadA.start();
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threadA.join();
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threadB.start();
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threadB.join();
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threadC.start();
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threadC.join();
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}
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/*
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* 使用信号量 Semaphore 类，三个线程每一个都有一个信号量，信号量等于 0 将被阻塞， 等于 1
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* 可以运行，因为每次只能有一个线程在运行，因此信号量总和应该为 1 ，相当于一个令牌在传递一样。
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*/
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private static void printTenTimesSemaphore() {
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final Semaphore semaphoreForA = new Semaphore(1); // A 最开始执行, 所以是 1
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final Semaphore semaphoreForB = new Semaphore(0);
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final Semaphore semaphoreForC = new Semaphore(0);
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final Thread threadA = new Thread() {
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@Override
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public void run() {
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for (int i = 0; i < 10; i++) {
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try {
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semaphoreForA.acquire();
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} catch (Exception e) {
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e.printStackTrace();
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} finally {
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System.out.print("A");
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semaphoreForB.release(); // 给 B 的信号加 1 ,让 B 可以获得信号去执行
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}
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}
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}
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};
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final Thread threadB = new Thread() {
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@Override
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public void run() {
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for (int i = 0; i < 10; i++) {
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try {
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semaphoreForB.acquire(); // 申请信号, 只有当信号量大于 0 时才不会被阻塞
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} catch (Exception e) {
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e.printStackTrace();
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} finally {
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System.out.print("B");
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semaphoreForC.release(); // 给 C 的信号加 1, 让 C 可以获得信号执行
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}
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}
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}
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};
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final Thread threadC = new Thread() {
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@Override
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public void run() {
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for (int i = 0; i < 10; i++) {
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try {
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semaphoreForC.acquire();
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} catch (Exception e) {
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e.printStackTrace();
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} finally {
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System.out.print("C");
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semaphoreForA.release();
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}
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}
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}
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};
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threadA.start();
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threadB.start();
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threadC.start();
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}
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/**
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* 使用 j.u.c 包中的原子变量，该变量的效果实际和令牌一样，只是根据该变量的状态来判断当前线程是不是可以运行，
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* 代码用到了 yield 方法，该方法可以让当前线程主动放弃执行权。
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*/
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private static void printTenTimes() {
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final AtomicInteger token = new AtomicInteger(0);
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final Thread threadA = new Thread() {
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@Override
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public void run() {
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for (int i = 0; i < 10; i++) {
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while (token.get() % 3 != 0) {
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yield(); // 不是 A 运行的时候, 让出执行权
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}
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System.out.print("A");
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token.incrementAndGet(); // 由于增加 1 后被 3 模余数 1, 而被 3 模余数 1 是 B 可以运行的, 此步相当于把令牌传递给 B
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}
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}
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};
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final Thread threadB = new Thread() {
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@Override
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public void run() {
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for (int i = 0; i < 10; i++) {
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while (token.get() % 3 != 1) {
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yield();
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}
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System.out.print("B");
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token.incrementAndGet();
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}
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}
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};
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final Thread threadC = new Thread() {
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@Override
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public void run() {
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for (int i = 0; i < 10; i++) {
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while (token.get() % 3 != 2) {
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yield();
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}
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System.out.print("C");
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token.incrementAndGet();
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}
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}
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};
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threadA.start();
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threadB.start();
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threadC.start();
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}
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/**
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* 使用 wait 和 notify 方法实现
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* 使用到了 BitSet 类，其中的 mutex 变量作为三个线程的互斥锁
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*/
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private static void printTenTimesWaitNotif () {
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final BitSet mutex = new BitSet (3);
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final Thread threadA = new Thread () {
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@Override
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public void run () {
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for (int i = 0; i < 10; i++) {
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try {
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synchronized (mutex) {
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while (!mutex.get (0)) {
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mutex.wait ();
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}
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System.out.print ("A");
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mutex.clear (0);
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mutex.set (1);
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mutex.notify ();
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}
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} catch (Exception e) {
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e.printStackTrace ();
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}
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}
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}
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};
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final Thread threadB = new Thread () {
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@Override
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public void run () {
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for (int i = 0; i < 10; i++) {
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try {
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synchronized (mutex) {
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while (!mutex.get (1)) {
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mutex.wait ();
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}
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System.out.print ("B");
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mutex.clear (1);
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mutex.set (2);
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mutex.notify ();
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}
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} catch (Exception e) {
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e.printStackTrace ();
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}
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}
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}
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};
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final Thread threadC = new Thread () {
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@Override
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public void run () {
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for (int i = 0; i < 10; i++) {
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try {
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synchronized (mutex) {
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while (!mutex.get (2)) {
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mutex.wait ();
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}
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System.out.print ("C");
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mutex.clear (2);
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mutex.set (0);
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mutex.notify ();
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}
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} catch (Exception e) {
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e.printStackTrace ();
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}
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}
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}
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};
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threadA.start ();
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threadB.start ();
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threadC.start ();
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synchronized (mutex) {
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mutex.set (0);
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mutex.notify ();
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}
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}
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}
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