Java语言ReadWriteLock特性实例测试

本文研究的主要是readwritelock特性，具体如下。

readwritelock几点特性

readlock 与 readlock 不互斥
readlock 与 writelock 互斥
writelock 与 readlock 互斥
writelock 与 writelock 互斥

举例来说:

线程1, 先拿到readlock, 线程2试图拿readlock, 可以拿到
线程1, 先拿到readlock, 线程2试图拿writelock, 阻塞等待,直到线程1释放锁之后才可以拿到
线程1, 先拿到writelock,线程2试图拿readlock, 阻塞等待,直到线程1释放锁之后才可以拿到
线程1, 先拿到writelock,线程2试图拿writelock, 阻塞等待,直到线程1释放锁之后才可以拿到

测试代码

package com.alioo.lock;
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 readwritelockdemo {
	static simpledateformat sdf = new simpledateformat("yyyy-mm-dd hh:mm:ss.sss");
	public static void main(string[] args) {
		data data = new data();
		worker t1 = new worker(data, false);
		//写
		worker t2 = new worker(data, true);
		//读
		worker t3 = new worker(data, true);
		//读
		t1.start();
		t2.start();
		t3.start();
	}
	static 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.read(); else
			    data.write();
		}
	}
	static class data {
		readwritelock lock = new reentrantreadwritelock();
		lock read = lock.readlock();
		lock write = lock.writelock();
		public void write() {
			try {
				thread.sleep(2000);
				//
			}
			catch (exception e) {
			}
			write.lock();
			system.out.println(thread.currentthread() + " write:begin "
			     + sdf.format(new date()));
			try {
				thread.sleep(5000);
				//
			}
			catch (exception e) {
			}
			finally {
				system.out.println(thread.currentthread() + " write:end "
				      + sdf.format(new date()));
				write.unlock();
			}
		}
		public int read() {
			read.lock();
			system.out.println(thread.currentthread()+ " read :begin "
			     + sdf.format(new date()));
			try {
				thread.sleep(5000);
				//
			}
			catch (exception e) {
			}
			finally {
				system.out.println(thread.currentthread() + " read :end "
				      + sdf.format(new date()));
				read.unlock();
			}
			return 1;
		}
	}
}

测试结果:

thread[thread-2,5,main] read :begin 2018-01-22 13:54:16.794
thread[thread-1,5,main] read :begin 2018-01-22 13:54:16.794
thread[thread-2,5,main] read :end 2018-01-22 13:54:21.795
thread[thread-1,5,main] read :end 2018-01-22 13:54:21.795
thread[thread-0,5,main] write:begin 2018-01-22 13:54:21.795
thread[thread-0,5,main] write:end 2018-01-22 13:54:26.795

测试结果解读:

同时启动了3个线程,其中1号线程thread[thread-0,5,main],执行write时先休眠了2秒.那么 2,3号线程thread[thread-1,5,main],thread[thread-2,5,main]将会优先执行代码

read.lock();

由于read.lock();是不互斥的(即可重入的),所以他们同时拿到了锁,通过日志可以看出来

thread[thread-2,5,main] read :begin 2018-01-22 13:54:16.794
thread[thread-1,5,main] read :begin 2018-01-22 13:54:16.794

而且他们执行的时间开销是相同的(测试代码中都是休眠5秒),所以也将同时执行结束

thread[thread-2,5,main] read :end 2018-01-22 13:54:21.795
thread[thread-1,5,main] read :end 2018-01-22 13:54:21.795

只有当所有的readlock被释放掉之后,writelock才能拿到锁,而这个时候thread[thread-1,5,main],thread[thread-2,5,main]执行结束后就会释放锁readlock

所以thread[thread-0,5,main]这个时候拿到了writelock并执行自己的业务代码

thread[thread-0,5,main] write:begin 2018-01-22 13:54:21.795
thread[thread-0,5,main] write:end 2018-01-22 13:54:26.795

总结

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