java的锁,synchronize和lock

了解这两个机制之前要先了解java的内存模型,详见我的另一篇文章java内存模型

简单的来说,synchronize是从jvm层面实现的,lock就是代码层面实现的

再输容易一点就是synchronize是机器控制的,lock就是你写的代码人控制的

直接看代码可能更直观一点

1,synchronize

public void test() {

     synchronized(this) {

          // todo your code

     }

}

 

此时，其效果等同于

public synchronized void test() {

     // todo your code

}

2,lock

public class Consumer implements Runnable {

 

     private Lock lock;

     public Consumer(Lock lock) {

            this. lock = lock;

     }

     @Override

     public void run() {

            // TODO Auto-generated method stub

            int count = 10;

            while( count > 0 ) {

                 try {

                      lock.lock();

                     count --;

                     System. out.print( "B");

                } finally {

                      lock.unlock(); //主动释放锁

                      try {

                           Thread. sleep(91L);

                     } catch (InterruptedException e) {

                            // TODO Auto-generated catch block

                           e.printStackTrace();

                     }

                }

           }

 

     }

}

public class Producer implements Runnable{

 

     private Lock lock;

     public Producer(Lock lock) {

            this. lock = lock;

     }

     @Override

     public void run() {

            // TODO Auto-generated method stub

            int count = 10;

            while (count > 0) {

                 try {

                      lock.lock();

                     count --;

                     System. out.print( "A");

                } finally {

                      lock.unlock();

                      try {

                           Thread. sleep(90L);

                     } catch (InterruptedException e) {

                            // TODO Auto-generated catch block

                           e.printStackTrace();

                     }

                }

           }

     }

}

public class Test {

     public static void main(String[] args) {

           Lock lock = new ReentrantLock();          

           Consumer consumer = new Consumer(lock);

           Producer producer = new Producer(lock);           

            new Thread(consumer).start();

            new Thread( producer).start();           

     }

}

在并发小的时候使用synchronize是不错的选择,因为jvm开销小,当并发大的时候就要用lock好好设计程序了!