跟mutex的区别是mutex是拿不到锁就睡眠，spinlock是拿不到锁就自旋。

自旋锁

自旋锁的概念有两种，一种是OS级别的自旋锁，也就是spinlock，另一种是语言平台实现的自旋，比如ReentrantLock。

ReentrantLock的自旋

image.png

Linux OS的自旋

pthread_spinlock_init 定义

image.png :::tips int pthread_spin_destroy(pthread_spinlock_t lock);
int pthread_spin_init(pthread_spinlock_t lock, int pshared); :::

  1. #include <stdio.h>
  2. #include <stdlib.h>
  3. #include <pthread.h>
  5. int sharei = 0;
  6. void increase_num(void);
  7. //定义一把自旋锁
  8. pthread_spinlock_t a_lock;
  10. int main()
  11. {
  12.     //初始化自旋锁
  13.   pthread_spin_init(&a_lock, 0);
  14.   int ret;
  15.   pthread_t thread1,thread2,thread3;
  16.   ret = pthread_create(&thread1,NULL,(void *)&increase_num,NULL);
  17.   ret = pthread_create(&thread2,NULL,(void *)&increase_num,NULL);
  18.   ret = pthread_create(&thread3,NULL,(void *)&increase_num,NULL);
  20.   pthread_join(thread1,NULL);
  21.   pthread_join(thread2,NULL);
  22.   pthread_join(thread3,NULL);
  24.   printf("sharei = %d\n",sharei);
  26.   return 0;
  27. }
  29. void increase_num(void)
  30. {
  31.   long i,tmp;
  32.   for(i =0;i<=9999;++i)
  33.   {
  34.     // lock spin 自旋
  35.     pthread_spin_lock(&a_lock);
  36.     tmp=sharei;
  37.     tmp=tmp+1;
  39.     sharei = tmp;
  40.     pthread_spin_unlock(&a_lock);
  42.   }
  43. }