第五章 线程同步

1. 重入锁

重入锁使用java.util.concurrent.locks.ReentrantLock类来实现。

public class ReenterLock implements Runnable{
    // 声明可重入锁，建议声明为static
    public static ReentrantLock lock = new ReentrantLock();
    public static int i = 0;
    @Override
    public void run() {
        for(int j=0; j<10000000; j++) {
            // 使用可重入锁保护临界资源
            lock.lock();
            try {
                i++;
            } finally {
                lock.unlock();
            }
        }
    }

    public static void main(String[] args) throws InterruptedException {
        ReenterLock reenterLock = new ReenterLock();
        Thread t1 = new Thread(reenterLock);
        ReenterLock reenterLock2 = new ReenterLock();
        Thread t2 = new Thread(reenterLock2);
        t1.start();
        t2.start();
        t1.join();
        t2.join();
        System.out.println(i);
    }
}

重入锁允许多次加锁，但是与之对应的释放锁次数也要一致。