代码demo

这是一把带超时时间的自旋锁，如果超时时间内依然无法获取锁，就直接返回false

  1. package org.example.spinlock;
  3. import java.util.concurrent.TimeUnit;
  4. import java.util.concurrent.atomic.AtomicBoolean;
  6. /**
  7.  * 自旋锁
  8.  */
  9. public class SpinLockTest {
  11.     public static void main(String[] args) {
  12.         SpinLock spinLock = SpinLock.get();
  13.         for (int i = 0; i < 3; i++) {
  14.             new Thread(()->{
  15.                 boolean success = spinLock.tryLock(2000);
  16.                 if (!success){
  17.                     System.out.println(Thread.currentThread().getName()+" get spin lock fail...");
  18.                     return;
  19.                 }
  21.                 System.out.println(Thread.currentThread().getName()+" get spin lock success...");
  22.                 try {
  23.                     TimeUnit.SECONDS.sleep(3);
  24.                 } catch (InterruptedException e) {
  25.                     e.printStackTrace();
  26.                 }
  27.                 System.out.println(Thread.currentThread().getName()+" TODO 业务逻辑...");
  28.                 spinLock.unLock();
  29.             }).start();
  30.         }
  32.     }
  33. }
  35. class SpinLock{
  37.     private SpinLock(){}
  39.     private final static SpinLock spinLock = new SpinLock();
  41.     public static SpinLock get(){
  42.         return spinLock;
  43.     }
  45.     private final AtomicBoolean available = new AtomicBoolean(false);
  47.     // 尝试获取锁，成功返回true，失败返回false
  48.     public boolean tryLock(long timeout){
  49.         long deadline = System.currentTimeMillis()+timeout;
  50.         while (System.currentTimeMillis()<deadline) {
  51.             if (available.compareAndSet(false, true)){
  52.                 return true;
  53.             }
  54.         }
  55.         return false;
  56.     }
  58.     public void unLock(){
  59.         available.compareAndSet(true,false);
  60.     }
  61. }

执行结果

  1. Thread-0 get spin lock success...
  2. Thread-1 get spin lock fail...
  3. Thread-2 get spin lock fail...
  4. Thread-0 TODO 业务逻辑...


思考

自旋锁如何设计能够最大程度降低空转时间？
（后期有空去优化，可以参考JDK AQS底层的自旋机制）