ReentrantLock介绍

重入锁（ReentrantLock）是一种递归无阻塞的同步机制,一个可重入的互斥锁定 Lock，它具有与使用 synchronized 方法和语句所访问的隐式监视器锁定相同的一些基本行为和语义，但功能更强大。

在Condition中，用await()替换wait()，用signal()替换notify()，用signalAll()替换notifyAll()，传统线程的通信方式，Condition都可以实现，这里注意，Condition是被绑定到Lock上的，要创建一个Lock的Condition必须用newCondition()方法。

Condition的强大之处在于它可以为多个线程间建立不同的Condition。

例子：接着synchronized的题目，改用ReentrantLock实现

public class TestLock implements Runnable {

    private int num;

    private int initNum;

    private Lock lock;

    private Condition thisCondtion;

    public TestLock(Lock lock, Condition thisCondtion, int num, int initNum) {
        this.lock = lock;
        this.thisCondtion = thisCondtion;
        this.num = num;
        this.initNum = initNum;
    }

    @Override
    public void run() {
        for (int i = 0; i < 6; i++) {
            try {
                lock.lock();
                while (initNum < num) {
                    thisCondtion.signal();
                    System.out.println(Thread.currentThread().getName() + ":" + initNum);
                    initNum++;
                    try {
                        thisCondtion.await();
                    } catch (InterruptedException e1) {
                        e1.printStackTrace();
                    }
                }
            } finally {
                lock.unlock();
            }

        }
    }

    public static void main(String[] args) {
        Lock lock = new ReentrantLock();
        Condition condition = lock.newCondition();
        TestLock testLock = new TestLock(lock, condition, 51, 1);
        Thread thread1 = new Thread(testLock, "线程1");
        Thread thread2 = new Thread(testLock, "线程2");
        thread1.start();
        try {
            thread1.sleep(100);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        thread2.start();
    }
}