Lock、synchronized、sleep和wait

最新推荐文章于 2024-11-06 09:24:58 发布

原创最新推荐文章于 2024-11-06 09:24:58 发布 · 454 阅读

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CC 4.0 BY-SA版权

文章标签：

#android #线程 #Lock #synchronized #wait

本文深入探讨了Java中Lock和synchronized关键字的区别，并通过实例代码详细解释了sleep与wait方法的不同之处，展示了如何利用wait和notify实现线程间的交互。

Lock和synchronized区别：
Lock能提供更多API，如trylock()：返回true表示拿到锁，false表示没有拿到锁；trylock(long time, TimeUnit unit):定义超时时间，避免死锁；unlock()：上锁后要在finally中调用unlock()去掉锁。
sleep和wait的区别：两者对线程的占用不同，看下面的代码：

public class Consumer implements Runnable{

    public void run() {
        // TODO Auto-generated method stub
        int count = 10;
        while(count > 0) {
             synchronized (Test. obj) {

                 System. out.print( "Consumer");
                 count --;
                 //Test. obj.notify();

                  try {
                       Test. obj.wait();

                 } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                       e.printStackTrace();
                 }
            }
       }
    }
}

public class Produce implements Runnable{

    public void run() {
        // TODO Auto-generated method stub
        int count = 10;
        while(count > 0) {
             synchronized (Test. obj) {

                  //System.out.print("count = " + count);
                 System. out.print( "Produce");
                 count --;
                 //Test. obj.notify();

                  try {
                       Test. obj.wait();
                 } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                       e.printStackTrace();
                 }
            }
        }
    }
}

public class Test {
    public static final Object obj = new Object();

    public static void main(String[] args) {

           new Thread( new Produce()).start();
           new Thread( new Consumer()).start();

    }
}

produce那个runnable先执行，之后wait，此时会释放obj的锁，然后Consumer拿到obj的锁，开始执行，最后结果：

ProduceConsumer

执行到Consumer就结束了，其实程序这时还在运行中，只是处于挂起状态，下面再在Consumer中加入notify:

public class Consumer implements Runnable{

    public void run() {
        // TODO Auto-generated method stub
        int count = 10;
        while(count > 0) {
             synchronized (Test. obj) {

                 System. out.print( "Consumer");
                 count --;
                 //挂起前释放锁
                 Test. obj.notify();

                  try {
                       Test. obj.wait();

                 } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                       e.printStackTrace();
                 }
            }
       }
    }
}

运行结果：
ProduceConsumerProduce
说明Consumer释放了对象锁，Produce重新拿到锁，那么为了让这两个线程轮流执行，每次wait前释放对象锁，即在wait前，调用notify:

public class Produce implements Runnable{

    public void run() {
        // TODO Auto-generated method stub
        int count = 10;
        while(count > 0) {
             synchronized (Test. obj) {

                  //System.out.print("count = " + count);
                 System. out.print( "Produce");
                 count --;
                 Test.obj.notify();

                  try {
                       Test. obj.wait();
                 } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                       e.printStackTrace();
                 }
            }
        }
    }
}

public class Consumer implements Runnable{

    public void run() {
        // TODO Auto-generated method stub
        int count = 10;
        while(count > 0) {
             synchronized (Test. obj) {

                 System. out.print( "Consumer");
                 count --;
                 Test. obj.notify();

                  try {
                       Test. obj.wait();

                 } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                       e.printStackTrace();
                 }
            }
       }
    }
}

结果：
ProduceConsumerProduceConsumerProduceConsumerProduceConsumerProduceConsumerProduceConsumerProduceConsumerProduceConsumerProduceConsumerProduceConsumer

sleep是线程的方法，线程调用后会让出cpu时间片，但并不能操作对象释放对象锁。