Android多线程研究（9）——读写锁

标签：java   读写锁   缓存器   lock   

一、什么是锁

在Java的util.concurrent.locks包下有关于锁的接口和类如下：

先看一段代码：

package com.codeing.snail.test;


public class ReadWriteLockTest {
	public static void main(String[] args) {
		final Output output = new Output();
		new Thread(){
			public void run() {
				while(true){
					output.output("CodeingSnail");
				}
			};
		}.start();
		
		new Thread(){
			public void run() {
				while(true){
					output.output("阳光小强");
				}
			};
		}.start();
	}
	
	static class Output{
		public void output(String name){
			char[] arry = name.toCharArray();
			for(int i = 0; i < arry.length; i++){
				System.out.print(arry[i]);
			}
			System.out.println();
		}
	}
}

输出的结果如下：

如果我们想让“CodeingSnail"和“阳光小强"两个字符串都能完整输出，就需要使用synchronized关键字将输出部分声明，如下：

		public synchronized void output(String name){
			char[] arry = name.toCharArray();
			for(int i = 0; i < arry.length; i++){
				System.out.print(arry[i]);
			}
			System.out.println();
		}

其实，除了synchronized关键字之外，还可以使用锁（Lock）来实现同步。

		ReentrantLock lock = new ReentrantLock();
		public void output(String name){
			lock.lock();
			try{
				char[] arry = name.toCharArray();
				for(int i = 0; i < arry.length; i++){
					System.out.print(arry[i]);
				}
				System.out.println();
			}finally{
				lock.unlock();
			}
		}

二、什么是读写锁

	class CachedData {
		Object data;
		volatile boolean cacheValid;
		final ReentrantReadWriteLock rwl = new ReentrantReadWriteLock();

		void processCachedData() {
		     rwl.readLock().lock();
		     if (!cacheValid) {
		        // Must release read lock before acquiring write lock
		        rwl.readLock().unlock();
		        rwl.writeLock().lock();
		        try {
		          // Recheck state because another thread might have
		          // acquired write lock and changed state before we did.
		          if (!cacheValid) {
		            data = ...
		            cacheValid = true;
		          }
		          // Downgrade by acquiring read lock before releasing write lock
		          rwl.readLock().lock();
		        } finally {
		          rwl.writeLock().unlock(); // Unlock write, still hold read
		        }
		     }

		     try {
		       use(data);
		     } finally {
		       rwl.readLock().unlock();
		     }
	     }
	}

Android多线程研究（9）——读写锁

标签：java   读写锁   缓存器   lock   

原文地址：http://blog.csdn.net/dawanganban/article/details/39300327