java 多线程-可重入锁

可重入锁：锁可以连续使用
计数器+判断进入的线程是不是已经锁定的线程，如果是那就不用等待，直接使用

public class my {public static void main(String[]args){     my m=new my();     m.test();}public void test(){    synchronized(this)//第一次获得锁    {        while(true)        {            synchronized(this)//第二次获得锁，假如没有可重入锁，将会造成死锁            {                System.out.println("relock");            }            try {                Thread.sleep(1000);            } catch (InterruptedException e) {                // TODO Auto-generated catch block                e.printStackTrace();            }        }    }}}

手工实现:

public class my {Lock lock=new Lock();public void a() throws InterruptedException{    lock.lock();    System.out.println(lock.getCount());    b();    lock.unlock();    System.out.println(lock.getCount());}public void b() throws InterruptedException{    lock.lock();    System.out.println(lock.getCount());    //..    lock.unlock();    System.out.println(lock.getCount());}public static void main(String[]args) throws InterruptedException{    my m=new my();    m.a();    Thread.sleep(1000);    System.out.println(m.lock.getCount());}}class Lock{//是否占用private boolean isLocked=false;private Thread lockedBy=null;//存储线程，如果是自身就不等了private int count=0;//使用锁public synchronized void lock() throws InterruptedException{    Thread t=Thread.currentThread();    while(isLocked&&lockedBy!=t)//如果被锁住了，且不是当前线程    {        wait();    }    isLocked=true;    lockedBy=t;    count++;}//释放锁public synchronized void unlock(){    if(Thread.currentThread()==lockedBy)    {        count--;        if(count==0)        {            isLocked=false;            notify();            lockedBy=null;        }    }    isLocked=false;    notify();}public int getCount() {    return count;}public void setCount(int count) {    this.count = count;}}