java中可重入锁和自旋锁

Posted 2020-10-31 hy7873

1、可重入锁：

也称为递归锁，当外层函数获得该锁之后，内层递归函数仍有获取该锁的代码，结果不受影响；

java中的synchronized  ReentrantLock都是可重的

举例：

public class Test implements Runnable{

    public synchronized void get(){
        System.out.println(Thread.currentThread().getId());
        set();
    }

    public synchronized void set(){
        System.out.println(Thread.currentThread().getId());
    }

    @Override
    public void run() {
        get();
    }
    public static void main(String[] args) {
        Test ss=new Test();
        new Thread(ss).start();
        new Thread(ss).start();
        new Thread(ss).start();
    }
}



public class Test implements Runnable {
    ReentrantLock lock = new ReentrantLock();

    public void get() {
        lock.lock();
        System.out.println(Thread.currentThread().getId());
        set();
        lock.unlock();
    }

    public void set() {
        lock.lock();
        System.out.println(Thread.currentThread().getId());
        lock.unlock();
    }

    @Override
    public void run() {
        get();
    }

    public static void main(String[] args) {
        Test ss = new Test();
        new Thread(ss).start();
        new Thread(ss).start();
        new Thread(ss).start();
    }
}

 

2、自旋锁

一个线程直接循环执行一个任务，不触发临界条件，另一个线程控制临界条件，另一个线程执行时可以使前一个线程停止执行。

例子：

public class SpinLock {

  private AtomicReference<Thread> sign =new AtomicReference<>();

  public void lock(){
    Thread current = Thread.currentThread();
    while(!sign .compareAndSet(null, current)){
    }
  }

  public void unlock (){
    Thread current = Thread.currentThread();
    sign .compareAndSet(current, null);
  }
}

　　

 

 

public class Test implements Runnable{

02

03	public synchronized void get(){

04	System.out.println(Thread.currentThread().getId());

05

set();

06

}

07

08	public synchronized void set(){

09	System.out.println(Thread.currentThread().getId());

10

}

11

12

@Override

13	public void run() {

14

get();

15

}

16	public static void main(String[] args) {

17	Test ss=new Test();

18	new Thread(ss).start();

19	new Thread(ss).start();

20	new Thread(ss).start();

21

}

22

}

01	public class Test implements Runnable {

02	ReentrantLock lock = new ReentrantLock();

03

04	public void get() {

05	lock.lock();

06	System.out.println(Thread.currentThread().getId());

07

set();

08	lock.unlock();

09

}

10

11	public void set() {

12	lock.lock();

13	System.out.println(Thread.currentThread().getId());

14	lock.unlock();

15

}

16

17

@Override

18	public void run() {

19

get();

20

}

21

22	public static void main(String[] args) {

23	Test ss = new Test();

24	new Thread(ss).start();

25	new Thread(ss).start();

26	new Thread(ss).start();

27

}

28

}