ReentrantReadWriteLock 的例子

引用

两个线程  来改动 同一个 map里面的值， 在debug状态可以看到 ， 只能同时一个线程 进行赋值， 因为有 writelock的 lock动作， 只有在一个lock 被unlock之后，才能另一线程 进入 进行修改。

同步阻塞

package com.base.concurrence.lock.reentrancereadwritelock;

public class ReentrancelockClient {
	static LockBody lb = new LockBody();
	
	public static void main(String[] args) {
		RunningTask rt1 = new RunningTask("FIRST", "RMB");
		RunningTask rt2 = new RunningTask("FIRST", "GBP");
		Thread t1 = new Thread(rt1);
		Thread t2 = new Thread(rt2);
		
		
		LockBody.Wallet wt_1 = new LockBody.Wallet();
		wt_1.currency = "JPY";
		
//		LockBody.Wallet wt_2 = new LockBody.Wallet();
//		wt_2.currency = "USD";
		
		lb.store("FIRST", wt_1);
		//lb.store("SECOND", wt_2);
		
		t1.start();
		t2.start();
		
		try {
			t1.join();
			t2.join();
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
		System.out.println(lb.getVal("FIRST").currency);
		//System.out.println(lb.getVal("SECOND").currency);
		
		
	}
	
	static class RunningTask implements Runnable{
		
		LockBody.Wallet newWt = new LockBody.Wallet();
		String keyPoint, newCurrency;
		
		public RunningTask(String key, String currency){
			keyPoint = key;
			newCurrency = currency;
		}
		
		@Override
		public void run() {
			lb.restore(keyPoint, newCurrency);
		}
		
	}
	
	
}

package com.base.concurrence.lock.reentrancereadwritelock;

import java.util.Map;
import java.util.TreeMap;
import java.util.concurrent.locks.ReentrantReadWriteLock;

public class LockBody {
	
	ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
	
	public static Map<String, Wallet> mp = new TreeMap<String, Wallet>();
	
	
	public void store(String key, Wallet wallet){
		lock.writeLock().lock();
		mp.put(key, wallet);
		lock.writeLock().unlock();
	}
	
	public Wallet getVal(String key){
		lock.readLock().lock();
		Wallet wt = mp.get(key);
		lock.readLock().unlock();
		return wt;
	}
	
	public void restore(String key, String currency){
		Wallet wallet = getVal(key);
		lock.writeLock().lock();
		wallet.currency = currency;
		lock.writeLock().unlock();
	}
	
	public static class Wallet{
		public String currency;
	}
}