java锁

import org.junit.Test;import java.util.ArrayList;import java.util.List;import java.util.concurrent.CompletableFuture;import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReentrantLock;import java.util.concurrent.locks.ReentrantReadWriteLock;/** * Created by ibm on 2017/5/24. * java中锁的机制三种： * 1.synchronized的关键字 * <1.实现简单，<2.性能不是最佳，是串行而非并行 * 2.重入锁ReentrantLock * <1.提供更强大的解锁功能，设置等待时间，优先相应终端，<2.性能不是最佳，是串行而非并行 * 3.读写锁 * <1.读写分离，<2.读绝对并行(经过测试，在查询过多或者缓慢的情况下，writeLock的效率是其他两者的10倍左右) */public class LockExercise {    private int value;    private static Lock reentrantLock = new ReentrantLock();    private static ReentrantReadWriteLock readWriteLock = new ReentrantReadWriteLock();    private static Lock readLock = readWriteLock.readLock();    private static Lock writeLock = readWriteLock.writeLock();    @Test    public void test(){        long st = System.currentTimeMillis();        List<CompletableFuture> cfs = new ArrayList<>();        LockExercise lockExercise = new LockExercise();        for(int i = 0 ; i < 20 ;i++){            int j = i;            cfs.add(CompletableFuture.runAsync(() -> {                try {                    lockExercise.handleRead4ReadWriteLock();                } catch (InterruptedException e) {                    e.printStackTrace();                }            }));        }        //等待所有线程执行完        CompletableFuture.allOf(cfs.toArray(new CompletableFuture[cfs.size()])).join();        System.out.println("value = " + lockExercise.value + " 耗时：" + (System.currentTimeMillis() - st) + " ms");    }    //value = 0 耗时：20731ms    private synchronized Object handleRead() throws InterruptedException {        Thread.sleep(1000);        return value;    }    //value = 19 耗时：20644 ms    private synchronized void  handleWrite(int value) throws InterruptedException {        Thread.sleep(1000);        this.value++;    }    //value = 0 耗时：20647 ms    private Object handleRead4ReentrantLock() throws InterruptedException {        try{            //模拟读操作,读操作的耗时越多，读写锁的优势就越明显（因为，重入锁总是要排队等待锁，而读写锁可以绝对并行）            reentrantLock.lock();            Thread.sleep(1000);            return value;        }finally {            //重入锁必须在finally中显示的释放锁            reentrantLock.unlock();        }    }    //value = 19 耗时：20667 ms    private void handleWrite4ReentrantLock(int value) throws InterruptedException {        try {            reentrantLock.lock();            Thread.sleep(1000);            this.value++;        }finally {            reentrantLock.unlock();        }    }    //value = 0 耗时：20667 ms    private Object handleRead4ReadWriteLock() throws InterruptedException {        try{            readLock.lock();            Thread.sleep(1000);            return value;        }finally {            readLock.unlock();        }    }    //value = 0 耗时：3609 ms    private void handleWrite4ReadWriteLock(int value) throws InterruptedException {        try {            writeLock.lock();            Thread.sleep(1000);            this.value++;        }finally {            writeLock.unlock();        }    }}