java - 多线程和锁

Question

在进入条件之前，我试图了解锁和多线程的工作原理。这是我目前正在测试的代码:

public class tester {
    private static int count = 0;

    public void incrementCount() {
        count++;
    }

    public int getCount() {
        return count;
    }

    public static void main(String[] args) throws InterruptedException {
        Thread thread1 = new Thread(new testing());
        Thread thread2 = new Thread(new testing());
        thread1.start();
        thread2.start();
        thread1.join();
        thread2.join();
        System.out.println(count);
    }
}

这是实现 Runnable 的部分:

public class testing implements Runnable {
    Lock lock = new ReentrantLock();
    tester in = new tester();

    public void run() {
        for (int i = 0; i < 1000; i++) {
            lock.lock();
            in.incrementCount();
            lock.unlock();

        }
    }
}

我遇到的问题是，我试图在 main 方法的末尾打印出 2000，但即使我使用了锁，它也从未真正达到 2000。帮助将不胜感激!

Answer 1

even though I am using locks.

您正在为两个线程中的每一个使用单独的锁。

如果你想让锁在线程之间协调，它们都需要使用同一个锁实例。否则毫无意义。

改成类似的东西

class Testing implements Runnable {
    private final Lock lock;

    // pass in the lock to use via the constructor
    // both threads need to receive the same lock
    Testing(Lock lock){ this.lock = lock; }           

    public void run() {
        for (int i = 0; i < 1000; i++) {
            lock.lock();
            Tester.incrementCount();
            lock.unlock();
        }
    }
}