读写锁

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

public class Data {
	SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    public  synchronized void  set(){
		System.out.println(Thread.currentThread().hashCode() + "set:begin" + sdf.format(new Date()));
	    try{
	    	Thread.sleep(5000);
	    }catch(Exception e){
	    	
	    }finally{
    		System.out.println(Thread.currentThread().hashCode() + "set:end" +sdf.format(new Date()));
	    }
	}
	
	public synchronized void get(){
		System.out.println(Thread.currentThread().hashCode() + "set:begin" + sdf.format(new Date()));
	    try{
	    	Thread.sleep(5000);
	    }catch(Exception e){
	    	
	    }finally{
    		System.out.println(Thread.currentThread().hashCode() + "set:end" +sdf.format(new Date()));
	    }
	}
}

　　

public class Worker extends Thread {
	Data data;
	boolean read;

	public Worker(Data data, boolean read) {
		this.data = data;
		this.read = read;
	}

	public void run() {
		if (read)
			data.get();
		else
			data.set();
	}
}

　　

public class ReadWriteLockDemo {
	public static void main(String args[]) {
		Data data = new Data();
		Worker thread1 = new Worker(data, true);
		Worker thread2 = new Worker(data, true);
		thread1.start();
		thread2.start();
	}
}

　　

上面的代码使用synchronized锁，用synchronized修饰的方法只能同时被一个线程访问，于是代码中两个线程要依次执行，结果如下

8637543set:begin2015-03-22 10:35:26
8637543set:end2015-03-22 10:35:31
22474382set:begin2015-03-22 10:35:31
22474382set:end2015-03-22 10:35:36

下面使用读写锁，只需要修改Data类就可以了

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

public class Data {
	SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
	ReadWriteLock lock = new ReentrantReadWriteLock();
	Lock read = lock.readLock();
	Lock write = lock.writeLock();
    public  void  set(){
		write.lock();
		System.out.println(Thread.currentThread().hashCode() + "set:begin" + sdf.format(new Date()));
	    try{
	    	Thread.sleep(5000);
	    }catch(Exception e){
	    	
	    }finally{
    		System.out.println(Thread.currentThread().hashCode() + "set:end" +sdf.format(new Date()));
    	    write.unlock();
	    }
	}
	
	public void get(){
　　　　　　　　　read.lock()
		System.out.println(Thread.currentThread().hashCode() + "set:begin" + sdf.format(new Date()));
	    try{
	    	Thread.sleep(5000);
	    }catch(Exception e){
	    	
	    }finally{
    		System.out.println(Thread.currentThread().hashCode() + "set:end" +sdf.format(new Date()));
　　　　　　　　　 read.unlock()
	    }
	}
}

同时读，结果

30771886set:begin2015-03-22 10:51:18
14718739set:begin2015-03-22 10:51:18
30771886set:end2015-03-22 10:51:23
14718739set:end2015-03-22 10:51:23

两个线程同时读取数据，同时执行结束，没有限制。

public class ReadWriteLockDemo {
	public static void main(String args[]) {
		Data data = new Data();
		Worker thread1 = new Worker(data, false);
		Worker thread2 = new Worker(data, true);
		thread1.start();
		thread2.start();
	}
}

　　第一个线程写， 第二个线程读

8637543set:begin2015-03-22 10:54:11
8637543set:end2015-03-22 10:54:16
4699264set:begin2015-03-22 10:54:16
4699264set:end2015-03-22 10:54:21

读写锁允许同时读，但不允许读写同时进行