java - 任何人都可以解释如何在 java 中使用 Reentrant Lock over Synchronized 和一些最好的例子

Question

当我在 http://javarevisited.blogspot.in/2013/03/reentrantlock-example-in-java-synchronized-difference-vs-lock.html 运行示例类时，我看到了与 synchronized 相同的行为。

Answer 1

这里有线程获取锁和释放锁的三种方式、方法。您可能想尝试使用 synchronized 关键字来实现这些。使用 ReentrantLock 的扩展功能和优势将变得显而易见。

public class DoorLockUsingLock {

    private int counter= 0;
    private Thread owner= null;
    private Lock l = new ReentrantLock();
    private Condition notLocked= l.newCondition();

    public void lockItDown() throws InterruptedException {
        l.lockInterruptibly();
        try {
            while ((counter> 0) && (owner!= Thread.currentThread())) {
                notLocked.await();
            }
            counter++;
            owner = Thread.currentThread();
        } finally {
            l.unlock();
        }
    }

    public void lockItDownUninterruptibly() {
        l.lock();
        try {
            while ((counter > 0) && (owner != Thread.currentThread())) {
                notLocked.awaitUninterruptibly();
            }
            counter++;
            owner= Thread.currentThread();
        } finally {
            l.unlock();
        }
    }

    public boolean tryLockItDown(long timeout, TimeUnit unit) throws InterruptedException {
        long time = unit.toNanos(timeout);
        long end = System.nanoTime() + time;
        boolean success = l.tryLock(timeout, unit);
        if (!success) {
            return false;
        }
        try {
            time = end- System.nanoTime();
            while ((counter> 0) && (owner != Thread.currentThread()) && (time > 0)) {
                notLocked.await(time, TimeUnit.NANOSECONDS);
                time = end - System.nanoTime();
            }
            if (time > 0) {
                counter++;
                owner = Thread.currentThread();
                return true;
            }
            return false;
        } finally {
            l.unlock();
        }
    }

    public void unlockIt() throws IllegalMonitorStateException {
        l.lock();
        try {
            if (counter== 0) {
                throw new IllegalMonitorStateException();
            }
            if (owner!= Thread.currentThread()) {
                throw new IllegalMonitorStateException();
            }
            counter--;
            if (counter == 0) {
                owner = null;
                notLocked.signal();
            }
        } finally {
            l.unlock();
        }
    }
}