第五章 線程同步

1. 重入鎖

重入鎖使用java.util.concurrent.locks.ReentrantLock類來實現。

public class ReenterLock implements Runnable{
    // 聲明可重入鎖，建議聲明爲static
    public static ReentrantLock lock = new ReentrantLock();
    public static int i = 0;
    @Override
    public void run() {
        for(int j=0; j<10000000; j++) {
            // 使用可重入鎖保護臨界資源
            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);
    }
}

重入鎖允許多次加鎖，但是與之對應的釋放鎖次數也要一致。