示例

创建两个线程，分别对全局变量进行 +1 操作,分别对比使用互斥锁和没有使用互斥锁

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>

static int global = 0;

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

void *do_thread(void *arg)
{
    int loops = *(int *)arg;
    int i,tmp = 0;

    for (i = 0;i < loops;i++){
        pthread_mutex_lock(&mutex);
        tmp = global;
        tmp++;
        global = tmp;
        pthread_mutex_unlock(&mutex);
    }

    pthread_exit(NULL);
}

int main(int argc,char *argv[])
{
    int err,i = 0;
    pthread_t tid[2] = {0};
    int loops = 0;

    if (argc != 2){
        fprintf(stderr,"Usage : < %s > < count loops>\n",argv[0]);
        exit(EXIT_FAILURE);
    }

    loops = atoi(argv[1]);

    for (i = 0;i < 2;i++){
        err = pthread_create(&tid[i],NULL,do_thread,&loops);
        if (err != 0){
            fprintf(stderr,"[ERROR] pthread_create(): < %s > \n",strerror(err));
            exit(EXIT_FAILURE);
        }
    }


    pthread_join(tid[0],NULL);
    pthread_join(tid[1],NULL);

    printf("global = %d\n",global);
    return 0;
}

• 没有使用互斥锁时，输出结果如下:

./a.out 1000000
global = 1321859

• 使用互斥锁后，输出结果如下:

global = 2000000

练习

使用互斥锁验证上述示例