ReentrantLock与synchronized的区别

       ReentrantLock 的lock机制有2种，忽略中断锁和响应中断锁，这给我们带来了很大的灵活性。比如：如果A、B2个线程去竞争锁，A线程得到了锁，B线程等待，但是A线程这个时候实在有太多事情要处理，就是 一直不返回，B线程可能就会等不及了，想中断自己，不再等待这个锁了，转而处理其他事情。这个时候ReentrantLock就提供了2种机制，第一，B线程中断自己（或者别的线程中断它），但是ReentrantLock 不去响应，继续让B线程等待，你再怎么中断，我全当耳边风（synchronized原语就是如此）；第二，B线程中断自己（或者别的线程中断它），ReentrantLock 处理了这个中断，并且不再等待这个锁的到来，完全放弃。请看例子：

 

/**
 * @version 0.10 2009-11-6
 * @author Zhang Hua
 */
public class Test {
    //是用ReentrantLock，还是用synchronized
    public static boolean useSynchronized = false;
    public static void main(String[] args) {
        IBuffer buff = null;
        if(useSynchronized){
            buff = new Buffer();
        }else{
            buff = new BufferInterruptibly();    
        }
        final Writer writer = new Writer(buff);
        final Reader reader = new Reader(buff);
        writer.start();
        reader.start();
        new Thread(new Runnable() {
            public void run() {
                long start = System.currentTimeMillis();
                for (;;) {
                    // 等5秒钟去中断读
                    if (System.currentTimeMillis() - start > 5000) {
                        System.out.println("不等了，尝试中断");
                        reader.interrupt();
                        break;
                    }

                }

            }
        }).start();
    }
}

interface IBuffer{
    public void write();
    public void read() throws InterruptedException;
}
class Buffer implements IBuffer{
    private Object lock;

    public Buffer() {
        lock = this;
    }

    public void write() {
        synchronized (lock) {
            long startTime = System.currentTimeMillis();
            System.out.println("开始往这个buff写入数据…");
            for (;;)// 模拟要处理很长时间
            {
                if (System.currentTimeMillis() - startTime > Integer.MAX_VALUE)
                    break;
            }
            System.out.println("终于写完了");
        }
    }

    public void read() {
        synchronized (lock) {
            System.out.println("从这个buff读数据");
        }
    }
}

class BufferInterruptibly implements IBuffer{

    private ReentrantLock lock = new ReentrantLock();

    public void write() {
        lock.lock();
        try {
            long startTime = System.currentTimeMillis();
            System.out.println("开始往这个buff写入数据…");
            for (;;)// 模拟要处理很长时间
            {
                if (System.currentTimeMillis() - startTime > Integer.MAX_VALUE)
                    break;
            }
            System.out.println("终于写完了");
        } finally {
            lock.unlock();
        }
    }

    public void read() throws InterruptedException{
        lock.lockInterruptibly();// 注意这里，可以响应中断
        try {
            System.out.println("从这个buff读数据");
        } finally {
            lock.unlock();
        }
    }

}

class Writer extends Thread {

    private IBuffer buff;

    public Writer(IBuffer buff) {
        this.buff = buff;
    }

    @Override
    public void run() {
        buff.write();
    }

}

class Reader extends Thread {

    private IBuffer buff;

    public Reader(IBuffer buff) {
        this.buff = buff;
    }

    @Override
    public void run() {

        try {
            buff.read();
        } catch (InterruptedException e) {
            System.out.println("我不读了");   
        }

        System.out.println("读结束");

    }
}