Java线程休眠和回复

Java帮帮

发布于 2018-08-06 17:37:12

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代码可运行

Java线程休眠和回复

sleep()方法：表示放弃当前cpu的资源，使当前线程不占用计算机的任何资源。如果当前线程获取到了锁，sleep（）方法是不会放弃锁的，如果线程被打断会抛出InterruptException异常。

join（）方法：当一个线程对接的join的方法被调用时，调用他的线程会被挂起，直到这个线程对象完成它的任务。

代码：

public class Test3 {
public static void main(String[] args) {Thread thread = new Thread(new Runnable() {@Overridepublic void run() {System.out.println("线程开始执行");try {
TimeUnit.SECONDS.sleep(3);} catch (InterruptedException e) {
e.printStackTrace();
}System.out.println("线程执行结束");
}});System.out.println("主线程执行");thread.start();try {thread.join();} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}System.out.println("主线程结束");}
}

执行结果：

主线程执行线程开始执行线程执行结束主线程结束

join方法：

public final synchronized void join(long millis)throws InterruptedException {long base = System.currentTimeMillis();long now = 0;if (millis < 0) {throw new IllegalArgumentException("timeout value is negative");}
if (millis == 0) {while (isAlive()) {wait(0);}} else {while (isAlive()) {long delay = millis - now;if (delay <= 0) {break;}wait(delay);now = System.currentTimeMillis() - base;}}}

可以看出join方法里一直在判断线程isAlive(),如果存活就wait(0),把线程处于等待状态，如果线程没有执行完成，那么join（）这个方法就一直没有执行问，主线程也不会继续往下执行。

wait()方法：线程必须在同步代码块（synchronized）中调用wait()方法，如果在同步代码块之外调用wait()方法，jvm将会抛出IllegalMonitorStateException。当一个线程调用wait()方法时，jvm会把这个线程陷入休眠，并释放掉锁，同时允许其他线程得到锁。

notify()或notifyAll()：在同步代码块中调用这2个方法可以唤醒调用wait()的线程。

列子：

public class Computer {private int counter = 0;
public synchronized void producer() {while (true) {if (counter >= 10) {try {
wait();} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}} else if (counter < 2) {for (int i = 0; i < 10; i++) {counter++;System.out.println("生产了一台电脑当前还有" + counter);}}notifyAll();}}
public synchronized void consumer() {while (true) {if (counter == 0) {try {wait();} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}} else if (counter > 0) {while (counter > 0) {counter--;System.out.println("消费一台电脑当前还有" + counter);}}notifyAll();}}
public int getCounter() {return counter;}
public void setCounter(int counter) {this.counter = counter;}
public static void main(String[] args) {Computer computer = new Computer();Thread producer = new Thread(new Producer(computer));Thread consumer = new Thread(new Consumer(computer));producer.start();consumer.start();}}

public class Consumer implements Runnable{private Computer computer;
public Consumer(Computer computer) {super();this.computer = computer;}@Overridepublic void run() {computer.consumer();}}

public class Producer implements Runnable{private Computer computer;public Producer(Computer computer) {super();this.computer = computer;}@Overridepublic void run() {
computer.producer();}}

输出结果：

生产了一台电脑当前还有8 生产了一台电脑当前还有9 生产了一台电脑当前还有10 消费一台电脑当前还有9 消费一台电脑当前还有8 消费一台电脑当前还有7 消费一台电脑当前还有6 消费一台电脑当前还有5 消费一台电脑当前还有4 消费一台电脑当前还有3 消费一台电脑当前还有2

在ReentrantLock挂起和唤醒线程需要使用Condition,一个ReentrantLock可以有多个Condition。调用await()使线程挂起并释放掉锁，signalAll()会唤醒线程。

修改Compuetr的代码 Producer 和 Consumer 代码不变：

import java.util.concurrent.locks.Condition;import java.util.concurrent.locks.ReentrantLock;public class Computer {private int counter = 0;private ReentrantLock lock;private Condition producerC;private Condition consumerC;private Computer(ReentrantLock lock) {this.lock = lock;producerC = lock.newCondition();consumerC = lock.newCondition();}public void producer() {while (true) {try {lock.lock();if (counter >= 10) {try {//线程挂起 并释放掉锁producerC.await();} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}} else if (counter < 2) {for (int i = 0; i < 10; i++) {counter++;System.out.println("生产了一台电脑当前还有" + counter);}}//把线程唤醒 线程需要重新获取锁consumerC.signalAll();} finally {lock.unlock();}}
}public void consumer() {while (true) {try {lock.lock();if (counter == 0) {try {  //线程挂起 并释放掉锁consumerC.await();} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}} else if (counter > 0) {while (counter > 0) {counter--;System.out.println("消费一台电脑当前还有" + counter);}}//把线程唤醒 线程需要重新获取锁producerC.signalAll();} finally {lock.unlock();}}}public int getCounter() {return counter;}public void setCounter(int counter) {this.counter = counter;}public static void main(String[] args) {ReentrantLock lock = new ReentrantLock();Computer computer = new Computer(lock);Thread producer = new Thread(new Producer(computer));Thread consumer = new Thread(new Consumer(computer));producer.start();consumer.start();
}
}

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原始发表：2018-07-28，如有侵权请联系 cloudcommunity@tencent.com 删除

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