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;
}

}