java多線程編程環(huán)境下并發(fā)是常見(jiàn)問(wèn)題，這兩天看了鎖相關(guān)的問(wèn)題，記錄下兩個(gè)簡(jiǎn)單的用鎖實(shí)現(xiàn)等待/喚醒機(jī)制的demo。

1.synchronized方式實(shí)現(xiàn)等待/喚醒。

public class WaitAndNotify {
    private static boolean flag = true;
    private static Object lock = new Object();
    public static void main(String[] args) {
        Thread waitThread = new Thread(new Wait(), "WaitThread");
        waitThread.start();
        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        Thread notifyThread = new Thread(new Notify(), "NotifyThread");
        notifyThread.start();
    }
    private static class Wait implements Runnable {
        @Override
        public void run() {
            synchronized (lock) {
                while (flag) {
                    System.out.println(Thread.currentThread() + " flag是true,wait。。" + new SimpleDateFormat("HH:mm:ss").format(new Date()));
                    try {
                        lock.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                System.out.println(Thread.currentThread() + " flag是false，開(kāi)始繼續(xù)工作" + new SimpleDateFormat("HH:mm:ss").format(new Date()));
            }
        }
    }
    private static class Notify implements Runnable {
        @Override
        public void run() {
            synchronized (lock){
                System.out.println(Thread.currentThread() + " 持有鎖，發(fā)出通知" + new SimpleDateFormat("HH:mm:ss").format(new Date()));
                lock.notifyAll();
                flag = false;
                try {
                    TimeUnit.SECONDS.sleep(5);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

打印結(jié)果：

Thread[WaitThread,5,main] flag是true,wait。。18:55:28
Thread[NotifyThread,5,main] 持有鎖，發(fā)出通知18:55:29
Thread[WaitThread,5,main] flag是false，開(kāi)始繼續(xù)工作18:55:34

分析：根據(jù)程序可以看到，大致的過(guò)程就是：WaitThread拿到lock對(duì)象的鎖，然后根據(jù)flag標(biāo)記，自己調(diào)用了wait()方法，從而釋放鎖并進(jìn)入WAITTING狀態(tài)。NotifyThread此時(shí)獲取了lock對(duì)象的鎖，然后進(jìn)行notify操作，此時(shí)WaitThread被喚醒，但是，它不能立刻執(zhí)行，因?yàn)閱拘丫€程N(yùn)otifyThread還持有“該對(duì)象的同步鎖”。必須等到NotifyThread線程釋放了“對(duì)象的同步鎖”之后，也就是同步代碼塊執(zhí)行完以后，即睡眠5秒以后，等待線程WaitThread才能獲取到“對(duì)象的同步鎖”進(jìn)而繼續(xù)運(yùn)行。

2.ReentrantLock方式實(shí)現(xiàn)等待/喚醒。

public class ReenterLockCondition {
    private static ReentrantLock lock = new ReentrantLock();
    private static Condition condition = lock.newCondition();
    private static Runnable runnable = () -> {
        try {
            lock.lock();
            System.out.println(Thread.currentThread().getName() + "進(jìn)入等待。。");
            condition.await();
            System.out.println(Thread.currentThread().getName() + "繼續(xù)執(zhí)行");
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    };
    public static void main(String[] args) throws InterruptedException {
        Thread thread = new Thread(runnable, "thread--1");
        thread.start();
        Thread.sleep(2000);
        lock.lock();
        condition.signal();
        System.out.println("主線程發(fā)出信號(hào)");
        lock.unlock();
    }
}

打印結(jié)果：

thread--1進(jìn)入等待。。
主線程發(fā)出信號(hào)
thread--1繼續(xù)執(zhí)行

分析：這里thread–1線程是等待線程，主線程就是喚醒想成。開(kāi)始thread-1啟動(dòng)，拿到鎖，然后進(jìn)入等待并且釋放鎖，2秒后，主線程拿到鎖，然后發(fā)出信號(hào)并釋放鎖，最后，thread–1繼續(xù)執(zhí)行。

以上就是關(guān)于“實(shí)現(xiàn)Java鎖的兩種機(jī)制”的介紹，大家如果想了解更多相關(guān)知識(shí)，不妨來(lái)關(guān)注一下動(dòng)力節(jié)點(diǎn)的Java視頻教程，里面的課程內(nèi)容由淺到深，通俗易懂，即使沒(méi)有基礎(chǔ)也可以聽(tīng)懂，希望對(duì)大家的學(xué)習(xí)能夠有所幫助。