mutex.c

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <pthread.h>
#define NUM_THREAD 100
void *thread_inc(void *arg);
void *thread_des(void *arg);

long long num = 0;
pthread_mutex_t mutex; //保存互斥量读取值的变量

int main(int argc, char *argv[])
{
    pthread_t thread_id[NUM_THREAD];
    int i;

    pthread_mutex_init(&mutex, NULL); //创建互斥量

    for (i = 0; i < NUM_THREAD; i++)
    {
        if (i % 2)
            pthread_create(&(thread_id[i]), NULL, thread_inc, NULL);
        else
            pthread_create(&(thread_id[i]), NULL, thread_des, NULL);
    }

    for (i = 0; i < NUM_THREAD; i++)
        pthread_join(thread_id[i], NULL);

    printf("result: %lld \n", num);
    pthread_mutex_destroy(&mutex); //销毁互斥量
    return 0;
}

void *thread_inc(void *arg)
{
    int i;
    pthread_mutex_lock(&mutex); //上锁
    for (i = 0; i < 50000000; i++)
        num += 1;
    pthread_mutex_unlock(&mutex); //解锁
    return NULL;
}
void *thread_des(void *arg)
{
    int i;
    pthread_mutex_lock(&mutex);
    for (i = 0; i < 50000000; i++)
        num -= 1;
    pthread_mutex_unlock(&mutex);
    return NULL;
}