java 线程——可重所锁&不可重入锁

不可重入锁

当前线程已经获取了锁，当这个线程再次尝试获取这个锁的时候就会获取不到被阻塞，我们来写一个不可重入锁的例子。

class Lock{
	private boolean lock = false;
	/**
	 * 加锁
	 * 当lock = true;说明当前对象拿着锁
	 */
	public synchronized void lock() throws Exception{
		while(lock){
			wait();
		}
		lock = true;
	}
	public synchronized void unlock(){
		lock = false;
		notify();
	}
}

可重入锁

当前线程获取了该锁之后还可以再次获取该锁。

class Lock2{
	private boolean lock = false;
	private Thread lockBy = null;
	private int lockCount = 0;
	
	public synchronized void lock() throws Exception{
		Thread thread = Thread.currentThread();
		while(lock && lockBy != thread){
			wait();
		}
		lock = true;
		lockBy = thread;
		lockCount ++;
	}
	public synchronized void unlock(){
		if(Thread.currentThread() == lockBy){
			lockCount--;
			if(lockCount == 0){
				lock = false;
				notify();
			}
		}
	}
}