pthread_mutex_lock线程锁使用简单示例

最新推荐文章于 2025-06-01 13:55:23 发布

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最新推荐文章于 2025-06-01 13:55:23 发布

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本文通过一个简单的示例介绍了pthread_mutex_lock线程锁的使用，演示了在多线程环境下如何保证数据的一致性。在加锁的情况下，两个线程交替修改整数，确保线程安全。当移除锁后，通过验证输出，可以观察到数据竞争的现象。

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#define __USE_LARGEFILE64
#define _LARGEFILE64_SOURCE
#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>
#include <dirent.h>
#include <string.h>
#include <pthread.h>
#define mutex_lock

pthread_mutex_t mutex;
void *thread_function_even(void *inpara)
{
int *num = (int *)inpara;
long unsigned int thread_num = pthread_self();
pthread_detach( thread_num ); /*detach to be an independent thread*/
while(1)
{
#ifdef mutex_lock
pthread_mutex_lock(&mutex);
#endif
*num = (*num * 2)% 100;
usleep(1);
printf("int thread_function_even,num:%d,is even:%d\n",*num, (0 == *num % 2) );
#ifdef mutex_lock
pthread_mutex_unlock(&mutex);
#endif
}
}
void *thread_function_odd(void *inpara)
{
int *num = (int *)inpara;
long unsigned int thread_num = pthread_self();
pthread_detach( thread_num ); /*detach to be an independent thread*/
while(1)
{
#ifdef mutex_lock
pthread_mutex_lock(&mutex);
#endif
*num = (*num * 2)% 100 + 1;
usleep(1);
printf("int thread_function_odd,num:%d,is even:%d\n",*num, (0 == *num % 2) );
#ifdef mutex_lock
pthread_mutex_unlock(&mutex);
#endif
}
}
int main (int argc, char *argv[])
{
/*mutex is a lock,everyone only can operate an array by get the mutex*/
#ifdef mutex_lock
pthread_mutex_init(&mutex, NULL);
#endif

/*create two threads,one change the num to even,the other change the num to odd*/
int i = 0;
pthread_t thread_even,thread_odd;
pthread_create(&thread_even, NULL, thread_function_even, &i);
pthread_create(&thread_odd, NULL, thread_function_odd, &i);

while(1);
#ifdef mutex_lock
pthread_mutex_destroy(&mutex);
#endif

}

1.编译:gcc main.c -lpthread -g

2.运行:./a > 1 十几秒后ctrl c停掉

3.验证锁是否有效，以下两条命令都搜不到结果：

cat 1|grep thread_function_odd|grep "even:1"
cat 1|grep thread_function_even|grep "even:0"

4.去掉代码中的锁：注释#define mutex_lock

5.去掉后验证不加锁后是否正确，步骤3中的两条命令能搜到结果

cat 1|grep thread_function_odd|grep "even:1"
cat 1|grep thread_function_even|grep "even:0"

6.代码的原理：创建两个线程，两个线程都操作同一个整数，一个只把整数变为偶数，一个只把整数变为奇数，加锁的情况下，偶数线程中打印的数字全为偶数，奇数线程中打印的数字全为奇数