Java线程通讯方式

Java线程通讯方式

线程间通信常用方式如下：

l  休眠唤醒方式：

Object的wait、notify、notifyAll

Condition的await、signal、signalAll

l  CountDownLatch：用于某个线程A等待若干个其他线程执行完之后，它才执行

l  CyclicBarrier：一组线程等待至某个状态之后再全部同时执行

l  Semaphore：用于控制对某组资源的访问权限

Object的wait、notify、notifyAll

public class WaitNotifyRunnable{ private Object obj = new Object(); private Integer i=0; public void odd() { while(i<10){ synchronized (obj){ if(i%2 == 1){ System.out.println("奇数："+i); i++; obj.notify(); } else { try { obj.wait(); } catch (InterruptedException e) { e.printStackTrace(); } } } } }

public void even(){ while(i<10){ synchronized (obj){ if(i%2 == 0){ System.out.println("偶数："+i); i++; obj.notify(); } else { try { obj.wait(); } catch (InterruptedException e) { e.printStackTrace(); }} } } } public static void main(String[] args){ final WaitNotifyRunnable runnable = new WaitNotifyRunnable(); Thread t1 = new Thread(new Runnable() { public void run() { runnable.odd(); } }, "偶数线程"); Thread t2 = new Thread(new Runnable() {public void run() { runnable.even(); } }, "奇数线程"); t1.start(); t2.start(); }}

Condition的await、signal、signalAll

import java.util.concurrent.locks.Condition;import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReentrantLock;public class WaitNotifyRunnable{ private Lock lock = new ReentrantLock(); private Condition condition = lock.newCondition(); private Integer i=0; public void odd() { while(i<10){ lock.lock(); try{ if(i%2 == 1){ System.out.println("奇数："+i); i++; condition.signal(); } else { condition.await(); } } catch (InterruptedException e) { e.printStackTrace(); } finally { lock.unlock(); } } } public void even(){ while(i<10){ lock.lock(); try{ if(i%2 == 0){ System.out.println("偶数："+i); i++; condition.signal(); } else { condition.await(); } } catch (InterruptedException e) { e.printStackTrace(); } finally { lock.unlock(); } } } public static void main(String[] args){ final WaitNotifyRunnable runnable = new WaitNotifyRunnable(); Thread t1 = new Thread(new Runnable() { public void run() { runnable.odd(); } }, "偶数线程"); Thread t2 = new Thread(new Runnable() { public void run() { runnable.even(); } }, "奇数线程"); t1.start(); t2.start(); }}

Object和Condition休眠唤醒区别

l  object wait()必须在synchronized（同步锁）下使用，

l  object wait()必须要通过Nodify()方法进行唤醒

l  condition await() 必须和Lock（互斥锁/共享锁）配合使用

l  condition await() 必须通过 signal() 方法进行唤醒

CountDownLatch方式

CountDownLatch这个类能够使一个线程等待其他线程完成各自的工作后再执行。

CountDownLatch是通过一个计数器来实现的，计数器的初始值为线程的数量

每当一个线程完成了自己的任务后，计数器的值就会减1。当计数器值到达0时，它表示所有的线程已经完成了任务，然后在闭锁上等待的线程就可以恢复执行任务

import java.util.concurrent.CountDownLatch;public class CoachRecerDemo { private CountDownLatch countDownLatch=new CountDownLatch(3); //设置要等待的运动员 //运动员方法 public void racer(){ //获取线程名 String name=Thread.currentThread().getName(); System.out.println(name+"正在准备...."); try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println(name+"准备完毕"); countDownLatch.countDown();//-1 } //教练方法 public void coach(){ String name=Thread.currentThread().getName(); System.out.println(name+"等待运动员准备..."); try { countDownLatch.await(); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("所有运动员就绪，"+name+"开始训练"); } public static void main(String[] args) { //1.创建CoachRecerDemo 实例 CoachRecerDemo coachRecerDemo=new CoachRecerDemo(); //2.创建三个线程对象 Thread thread1=new Thread(new Runnable(){ public void run() { coachRecerDemo.racer(); } },"运动员1"); Thread thread2=new Thread(new Runnable() { public void run() { coachRecerDemo.racer(); } },"运动员2"); Thread thread3=new Thread(new Runnable() { public void run() { coachRecerDemo.racer(); } },"运动员3"); //3.教练 Thread thread4=new Thread(new Runnable() { public void run() { coachRecerDemo.coach(); } },"教练"); thread4.start(); thread1.start(); thread2.start(); thread3.start(); }}

CyclicBarrier方式

CyclicBarrier是在java1.5被引入的，存在于java.util.concurrent包下。

CyclicBarrier实现让一组线程等待至某个状态之后再全部同时执行。

CyclicBarrier底层是三个线程同时启动

import java.util.Date;import java.util.concurrent.BrokenBarrierException;import java.util.concurrent.CyclicBarrier;public class ThreeThreadStartDemo { private CyclicBarrier cyclicBarrier = new CyclicBarrier(3);// 所有参与启动的线程数 public void startThread() { // 打印线程准备启动 String name = Thread.currentThread().getName(); System.out.println(name + "正在准备..."); // 2.调用CyclicBarriar的await方法等待线程准备完毕 try { cyclicBarrier.await(); } catch (InterruptedException | BrokenBarrierException e) { // TODO Auto-generated catch block e.printStackTrace(); } // 3.打印线程启动信息 System.out.println(name + "已经启动完毕" + new Date().getTime()); } public static void main(String[] args) { final ThreeThreadStartDemo threadStartDemo = new ThreeThreadStartDemo(); Thread thread1 = new Thread(new Runnable() { public void run() { threadStartDemo.startThread(); } }); Thread thread2 = new Thread(new Runnable() { public void run() { threadStartDemo.startThread(); } }); Thread thread3 = new Thread(new Runnable() { public void run() { threadStartDemo.startThread(); } }); thread1.start(); thread2.start(); thread3.start(); } }

Semaphore方式

Semaphore是在java1.5被引入的，存在于java.util.concurrent包下。

Semaphore用于控制对某组资源的访问权限。

import java.util.concurrent.Semaphore;public class WorkerMachineDemo { static class Work implements Runnable { private int workerNum; private Semaphore semaphore; public Work(int workerNum, Semaphore semaphore) { this.workerNum = workerNum; this.semaphore = semaphore; } public void run() { // 1.获取机器 // 2.打印工人获取到机器，开始工作 // 3.线程睡眠1000毫秒 // 4.使用完毕 try { semaphore.acquire(); String name = Thread.currentThread().getName(); System.out.println(name + "获取到机器，开始工作"); Thread.sleep(1000); semaphore.release(); System.out.println(name + "使用完毕，释放机器！"); } catch (Exception e) { // TODO: handle exception } } } public static void main(String[] args) { int works = 8; Semaphore semaphore = new Semaphore(3);// 机器数 for (int i = 0; i < works; i++) { new Thread(new Work(i, semaphore)).start(); } }}

sleep和wait区别：

wait和notify区别

wait和notify都是Object中的方法

wait和notify执行前线程都必须获得对象锁

wait的作用是使当前线程进行等待

notify的作用是通知其他等待当前线程的对象锁的线程

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