ReentrantReadWriteLock读写锁

合理使用ReentrantReadWriteLock能相对于ReentrantLock提高不少效率，ReentrantReadWriteLock有两种锁一种是读操作相关的锁称为“”共享锁“” ，另外一种是与写相关的锁称为“”排他锁“”。使用ReentrantReadWriteLock很好地将读写分离，使得读读可以共享(不需要同步)，读写互斥，写读互斥，写写互斥。下面写测试下 读读共享，读写互斥，写读互斥，写写互斥。

1 新建一个service类：

public class MyService {

private ReentrantReadWriteLock lock = new ReentrantReadWriteLock();

private int number = 100;

public void readService1(){//读服务1
lock.readLock().lock();
System.out.println(number);
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
lock.readLock().unlock();
}

public void readService2(){//读服务2
lock.readLock().lock();
System.out.println(number);
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
lock.readLock().unlock();
}

public void writeService1(){//写服务1
lock.writeLock().lock();
number++;
System.out.println("number+1:"+number);
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
lock.writeLock().unlock();
}

public void writeService2(){//写服务2
lock.writeLock().lock();
number--;
System.out.println("number-1:"+number);try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
lock.writeLock().unlock();
}
}

2 新建一个测试了:
public class Test {

public static void main(String[] args) {

MyService service = new MyService();

Thread readThread1 = new Thread(new Runnable() {
@Override
public void run() {
service.readService1();
}
});

Thread readThread2 = new Thread(new Runnable() {
@Override
public void run() {
service.readService2();
}
});

Thread writeThread1 = new Thread(new Runnable() {
@Override
public void run() {
service.writeService1();
}
});

Thread writeThread2 = new Thread(new Runnable() {
@Override
public void run() {
service.writeService2();
}
});

// 下面四行代码两两组合运行验证读写锁，读读共享，读写互斥，写读互斥，写写互斥

readThread1.start();//读线程1
readThread2.start();//读线程2
// writeThread1.start();//写线程1
// writeThread2.start();//写线程2
}
}

下面我说明下每种组合测试的实验结果：
readThread1.start();

readThread2.start();

说明：读读线程将不会同步执行，因为他们之间锁共享。控制台会很快打印出两个 100 不会看到延迟效果

readThread1.start();

writeThread1.start();

说明：读写线程将会同步执行，因为他们之间锁排斥。控制台会先打印 100 然后 等待两秒 打印出：number+1:101

writeThread1.start();

writeThread2.start();

说明：写写线程将会同步执行，因为他们之间锁排斥。控制台会先打印 number+1:101 然后 等待两秒 打印出：number-1:100

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