Java锁机制ReentrantLock

ReentrantLock 锁常用于保证程序的人为顺序执行。

写一个类模拟ReentrantLock类的功能

class MyLock{
    private boolean lock = false;
    private int holdCount = 0;
    private Thread myThread = null; //当前占用锁的线程
    public synchronized void lock(){ //线程同步，只允许一个线程来获取这把锁
        Thread currThread = Thread.currentThread();   //当前访问线程
        if(lock == true && currThread != myThread){
            try {
                wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        //给予锁
        myThread = currThread;
        lock = true;
        holdCount ++;
    }
    public synchronized  void unlock(){
        Thread currThread = Thread.currentThread();   //当前访问线程
        if(currThread == myThread && holdCount>0){
            holdCount -- ;
            if(holdCount == 0){
                notifyAll();
                lock = false;
                myThread = null;
            }
        }
    }

    public int getHoldCount() {
        return holdCount;
    }
}

当一个线程不能得到一把锁时就会产生等待，等到其他线程释放锁后其将被唤醒，然后拿到所继续运行。

public class Test {
    public static void main(String[] args) {
        MyLock myLock = new MyLock();
        new Thread(new Runnable() {
            @Override
            public void run() {
                myLock.lock();
                System.out.println(Thread.currentThread().getName()+"得到锁:"+myLock.getHoldCount());
                myLock.lock();  //可重入锁
                System.out.println(Thread.currentThread().getName()+"重入成功:"+myLock.getHoldCount());
                myLock.unlock();
                System.out.println(Thread.currentThread().getName()+"释放锁:"+myLock.getHoldCount());
                myLock.unlock();
                System.out.println(Thread.currentThread().getName()+"释放锁:"+myLock.getHoldCount());
            }
        }).start();
        new Thread(new Runnable() {
            @Override
            public void run() {
                myLock.lock();
                System.out.println(Thread.currentThread().getName()+"得到锁:"+myLock.getHoldCount());
                myLock.unlock();
                System.out.println(Thread.currentThread().getName()+"释放锁:"+myLock.getHoldCount());
            }
        }).start();
    }
}

ReentrantLock的使用

public class LockTest {
    ReentrantLock lock = new ReentrantLock();
    public void a() throws InterruptedException {
        lock.lock();
        System.out.println(lock.getHoldCount());
        dosomething();
        lock.unlock();
        System.out.println(lock.getHoldCount());
    }
    public void dosomething() throws InterruptedException {
        lock.lock();
        System.out.println(lock.getHoldCount());
        lock.unlock();
        System.out.println(lock.getHoldCount());
    }
    public static void main(String[] args) throws InterruptedException {
        LockTest lockTest = new LockTest();
        lockTest.a();
    }
}