Linux操作系统的三种锁机制

Java程序员也要知道一些底层知识

一、Linux操作系统的三种锁机制：互斥锁（metux）、自旋锁（Spin）、信号量

 

二、互斥锁-C语言使用-Java锁会调用

 

 

 1）代码编译指令： gcc mutextest.c -o mutextest.out -pthread

2） C语言代码：

  

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
//声明全局变量sharei 和 方法
int sharei = 0;
void increase_num(void);
// add mutex --定义一个互斥锁并初始化
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
//主函数
int main()
{
  int ret;
  pthread_t thread1,thread2,thread3;
  ret = pthread_create(&thread1,NULL,(void *)&increase_num,NULL);
  ret = pthread_create(&thread2,NULL,(void *)&increase_num,NULL);
  ret = pthread_create(&thread3,NULL,(void *)&increase_num,NULL);
  // join 主线程等待子线程执行完成以后才结束
  pthread_join(thread1,NULL);
  pthread_join(thread2,NULL);
  pthread_join(thread3,NULL);
  printf("sharei = %d\n",sharei);
  return 0;
}
//run
void increase_num(void)
{
  long i,tmp;
  for(i =0;i<=9999;++i)
  {
     
    //上锁
    pthread_mutex_lock(&mutex);
    
    //不加锁 结果会小于30000 ，加锁以后结果正确=3000
    tmp=sharei;
    tmp=tmp+1;
    
    sharei = tmp;
    //解锁
    pthread_mutex_unlock(&mutex);
    
  }
}

　　三、自旋锁-C语言使用（Spin）

    

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
int sharei = 0;
void increase_num(void);
//定义一把自旋锁
pthread_spinlock_t a_lock;
int main()
{
    //初始化自旋锁
  pthread_spin_init(&a_lock, 0);
  int ret;
  pthread_t thread1,thread2,thread3;
  ret = pthread_create(&thread1,NULL,(void *)&increase_num,NULL);
  ret = pthread_create(&thread2,NULL,(void *)&increase_num,NULL);
  ret = pthread_create(&thread3,NULL,(void *)&increase_num,NULL);
  pthread_join(thread1,NULL);
  pthread_join(thread2,NULL);
  pthread_join(thread3,NULL);
  printf("sharei = %d\n",sharei);
  return 0;
}
void increase_num(void)
{
  long i,tmp;
  for(i =0;i<=9999;++i)
  {
    // lock spin 自旋
    pthread_spin_lock(&a_lock);
    tmp=sharei;
    tmp=tmp+1;
    
    sharei = tmp;
    pthread_spin_unlock(&a_lock);
    
  }
}