Java不可重入锁和可重入锁的简单代码实现

Java多线程的wait()方法和notify()方法:

• wait()：阻塞当前线程
• notify()：唤起被wait()阻塞的线程

这两个方法是成对出现和使用的，要执行这两个方法，有一个前提就是，当前线程必须获其对象的monitor（“锁”），否则会抛出IllegalMonitorStateException异常，所以这两个方法必须在同步块代码里面调用。
 

不可重入锁:

public class Lock{
    private boolean isLocked = false;
    public synchronized void lock() throws InterruptedException{
        while(isLocked){    
            wait();
        }
        isLocked = true;
    }
    public synchronized void unlock(){
        isLocked = false;
        notify();
    }
}
//使用
class Count{
    Lock lock = new Lock();
    public void print(){
        lock.lock();
        doAdd();
        lock.unlock();
    }
    public void doAdd(){
        lock.lock();
        //do something
        lock.unlock();
    }
}

可重入锁:

public class Lock{
    boolean isLocked = false;
    Thread  lockedBy = null;
    int lockedCount = 0;
    public synchronized void lock()
            throws InterruptedException{
        Thread thread = Thread.currentThread();
        while(isLocked && lockedBy != thread){
            wait();
        }
        isLocked = true;
        lockedCount++;
        lockedBy = thread;
    }
    public synchronized void unlock(){
        if(Thread.currentThread() == this.lockedBy){
            lockedCount--;
            if(lockedCount == 0){
                isLocked = false;
                notify();
            }
        }
    }
}
//使用
class Count{
    Lock lock = new Lock();
    public void print(){
        lock.lock();
        doAdd();
        lock.unlock();
    }
    public void doAdd(){
        lock.lock();
        //do something
        lock.unlock();
    }
}