公平锁和非公平锁

公平锁表示线程获取锁的顺序是按照线程加锁的顺序来分配的,即先来先得的FIDO先进先出顺序.

非公平锁就是一种获取锁的抢占机制,是随机获得锁的.

public class DemoService {

    private Lock lock;

    public DemoService(Boolean isFair) {
        this.lock = new ReentrantLock(isFair);
    }

    public void print() {
        lock.lock();
        try {
            System.out.println("ThreadName=" + Thread.currentThread().getName() + "锁定");
        } finally {
            lock.unlock();
        }

    }
}

public class Test {
    public static void main(String[] args) {
        DemoService service = new DemoService(true);

        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                System.out.println("Thread:" + Thread.currentThread().getName());
                service.print();
            }
        };

        Thread[] thread = new Thread[10];
        for (int i = 0; i < 10; i++) {
            thread[i] = new Thread(runnable);
        }
        for (int i = 0; i < 10; i++) {
            thread[i].start();
        }
    }
}

image.png

打印的结果基本呈有序状态，这就是公平锁的特点。

将Test类中的ture改为false就变成了非公平锁了：

image.png

非公平锁运行结果基本是乱序的，说明先start的线程不一定先获得锁。