ReentrantReadWriteLock具體作用

 通常情況下，使用synchronize就可以實現鎖，但有些業務場景的時候不適合使用這個，synchronize本身無序的非公平鎖，所以可能出現 多個線程一起讀取，因爲有其他線程更改過了，讀取的數據不一樣。以下是我寫的demo，可以看出readWriteLock的所用。讀寫鎖非常適合高頻讀取，又必須不能出現誤差的場景，如行情信息等

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package com.yy.test.lock;

import java.util.Random;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/**
 * @author yongyang
 * 讀寫鎖
 */
public class WirteReadLock_HasLock_wr {
	
	static Integer v = 0;
	public static void main(String[] args) {
		ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
		ExecutorService es =Executors.newFixedThreadPool(10);
		//會讀會寫的
		es.submit(new Runnable() {
			
			@Override
			public void run() {
				while(true) {
					try {
						lock.writeLock().lock();
						v++;
						System.out.println(Thread.currentThread().getId() + ":" + (v-1) + ">" +v);
					} finally {
						lock.writeLock().unlock();
					}
					
						
					
				}
			}
		});
		//只讀不寫的
		for (int i = 0; i < 9; i++) {
			
			es.submit(new Runnable() {
				
				@Override
				public void run() {
					while(true) {
						try {
							lock.readLock().lock();
							System.out.println(Thread.currentThread().getId() + ":" + v );
						} finally {
							lock.readLock().unlock();
						}
					}
					
				}
			});
		}
		
	}

}

 

package com.yy.test.lock;

import java.util.Random;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
 * @author yongyang
 * 讀寫鎖
 */
public class WirteReadLock_HasLock_sync {
	
	static Integer v = 0;
	public static void main(String[] args) {
		
		ExecutorService es =Executors.newFixedThreadPool(10);
		//會讀會寫的
		es.submit(new Runnable() {
			
			@Override
			public void run() {
				while(true) {
					synchronized (v) {
						v++;
						System.out.println(Thread.currentThread().getId() + ":" + (v-1) + ">" +v);
					}
				}
			}
		});
		//只讀不寫的
		for (int i = 0; i < 9; i++) {
			
			es.submit(new Runnable() {
				
				@Override
				public void run() {
					while(true)
					System.out.println(Thread.currentThread().getId() + ":" + v );
				}
			});
		}
		
	}

}