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();     } }