public interface ReadWriteLock
ReadWriteLock 维护了一对相关的锁，一个用于只读操作，另一个用于写入操作。只要没有 writer，读取锁可以由多个 reader 线程同时保持。写入锁是独占的。public abstract interface ReadWriteLock
{
public abstract Lock readLock();
public abstract Lock writeLock();
}访问约束
| read | write | |
|---|---|---|
| read | 非阻塞 | 阻塞 |
| write | 阻塞 | 阻塞 |
ReentrantReadWriteLock诞生于J·U·C。此后，国人一般称它为读写锁。人如其名，人如其名，她就是一个可重入锁，同时她还是一个读、写锁。
ReentrantReadWriteLock实现了ReadWriteLock和Serializable，同时ReadWriteLock跟Lock也没有继承关系。
ReentrantReadWriteLock跟ReentrantLock只有朋友关系，她们都是一个可重入锁。
eg:
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
public class ReadWriteLockTest implements Runnable{
private static ReentrantLock rl = new ReentrantLock();
private static ReentrantReadWriteLock readwriteLock = new ReentrantReadWriteLock();
private static Lock readLock = readwriteLock.readLock();
private static Lock writeLock = readwriteLock.writeLock();
public void handleRead(Lock lock) throws InterruptedException{
try{
lock.lock();
Thread.sleep(1000);
System.out.println(Thread.currentThread().getName() + " 获得了读锁, 时间为" +
System.currentTimeMillis());
}finally{
lock.unlock();
}
}
public void handleWrite(Lock lock) throws InterruptedException{
try{
lock.lock();
Thread.sleep(1000);
System.out.println(Thread.currentThread().getName() + " 获得了写锁, 时间为" +
System.currentTimeMillis());
}finally{
lock.unlock();
}
}
@Override
public void run() {
}
public static void main(String[] args) {
final ReadWriteLockTest rwlt = new ReadWriteLockTest();
Runnable read = new Runnable(){
public void run(){
try {
rwlt.handleRead(readLock);
//rwlt.handleRead(rl); //假如使用普通的重入锁，读写之间相互等待
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
Runnable write = new Runnable(){
public void run(){
try{
rwlt.handleWrite(writeLock);
//rwlt.handleWrite(rl); //假如使用普通的重入锁，读写之间相互等待
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
Thread[] readThread = new Thread[10];
for (int i = 0; i < 10; i++) {
readThread[i] = new Thread(read);
readThread[i].start();
}
Thread[] writeThread = new Thread[5];
for (int i = 0; i < 5; i++) {
writeThread[i] = new Thread(write);
writeThread[i].start();
}
}
}