java锁（2）公平锁

废话不多说，直接上实例：
public class Test04 {
public static void main(String[] args) {
ExecutorService es = Executors.newCachedThreadPool();
Some01 some = new Some01();
for (int i = 0; i < 10; i++) {
Runnable thread = new MyTread01(some);
es.execute(thread);
}
}

}

class MyLock {
volatile Thread first; // 队首线程
volatile Boolean isLock = false; // 锁状态字
volatile BlockingQueue<Thread> waitThread = new ArrayBlockingQueue<Thread>(20); // 等待队列,使用阻塞队列

// 上锁
synchronized void lock() throws InterruptedException {
    Thread nowThread = Thread.currentThread();
    while (isLock) { // 锁已被占用，则直接进入等待队列
        waitThread.put(nowThread);
        System.out.println(nowThread.getName() + "进入等待队列");
        wait();
    }
    if (waitThread.isEmpty()) { // 等待队列为空则直接获得锁
        isLock = true;
        System.out.println(nowThread.getName() + "直接获得锁");
    } else {
        while (nowThread != first) { // 不是队首线程则阻塞
            wait();
        }
        isLock = true;
        System.out.println("队首" + nowThread.getName() + "获得锁");
        Thread ft = waitThread.poll(); // 获取到锁后移除队首线程
        System.out.println("等待队列移除" + ft.getName());
    }

}

// 解锁
synchronized void unLock() {
    isLock = false;
    first = waitThread.peek(); // 获取等待队列队首线程,注意不移除
    notifyAll(); // 没有唤醒指定线程的方法，直接唤醒所有。
}

}

//共享资源
class Some01 {
private MyLock lock;

public Some01() {
    this.lock = new MyLock();
}

public void lock() throws InterruptedException {
    lock.lock();
}

public void unLock() {
    lock.unLock();
}

}

//自定义线程
class MyTread01 implements Runnable {
private Some01 some;

public MyTread01(Some01 some) {
    this.some = some;
}

public void run() {
    try {
        some.lock();
        System.out.println(Thread.currentThread().getName() + "开始工作");
        Thread.currentThread().sleep(300);
        System.out.println(Thread.currentThread().getName() + "结束工作");
        some.unLock();
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}

}

运行结果为 公平锁结果.PNG
突然发现Thread是真的不好用，根本没有办法唤醒指定线程，只能转为直接唤醒所有线程，然后判断是否为队首线程，不是则再次堵塞，

由此可以类推非公平锁的实现，就是将判断是否为队首线程的判断去掉，不再维护等待线程的顺序性，完全由线程间直接竞争，但是效率的确是会比公平锁高。