Linux使用C语言实现通过互斥锁限制对共享资源的访问

news2025/4/8 11:35:06

互斥锁限制共享资源的访问

主线程中有两个线程，分别输出信息。

#include <stdio.h>
#include <pthread.h>
#include <unistd.h>

int g_data=0;


void* fun1(void *arg)
{
        printf("t1：%ld thread is create\n", (unsigned long)pthread_self());
        printf("t1: %d\n", *((int*)arg));
        
        while(1){
                printf("t1:%d\n", g_data++);
                sleep(1);
        }
}

void* fun2(void *arg)
{
        printf("t2：%ld thread is create\n", (unsigned long)pthread_self());
        printf("t2: %d\n", *((int*)arg));
        while(1){
                printf("t2:%d\n", g_data++);
                sleep(1);
        }
}

int main()
{

        int ret;
        int param = 100;
        pthread_t t1;
        pthread_t t2;


        //                       线程属性 线程函数 线程函数参数
        ret = pthread_create(&t1, NULL, fun1, (void*)&param);
        if(ret == 0){
                printf("main:create t1 success\n");
        } else {
                perror("why t1 fail");
        }

        ret = pthread_create(&t2, NULL, fun2, (void*)&param);
        if(ret == 0){
                printf("main:create t1 success\n");
        } else {
                perror("why t2 fail");
        }

        printf("main:%ld\n", (unsigned long)pthread_self());//打印主线程ID

        while(1){
                printf("main:%d\n", g_data);
                sleep(1);
        }

        pthread_join(t1, NULL);//等待线程结束，防止进程结束，线程还未执行完毕
        pthread_join(t2, NULL);//等待线程结束，防止进程结束，线程还未执行完毕

        return 0;
}

如何能确保 3 一定在线程1 中输出呢？我们就需要用到“锁”这个东西了。
一定要线程1 先运行并且保证能输出3。
t1刚开始执行到while循环时候，就让它加锁，不让其它线程对共享资源访问【无论是否t2先执行，最终1s后都会轮到t1加锁，因为t2中释放锁后存在sleep函数，而t1没有】，循环一直执行，直到等到3 结束。因为当t1执行while循环时，t2就不能对g_data进行修改。

加锁后的修改：

//demo6
#include <stdio.h>
#include <pthread.h>
#include <unistd.h>

int g_data=0;
pthread_mutex_t mutex;

void* fun1(void *arg)
{
        printf("t1：%ld thread is create\n", (unsigned long)pthread_self());
        printf("t1: %d\n", *((int*)arg));
        pthread_mutex_lock(&mutex);
        while(1){
                printf("t1:%d\n", g_data++);
                sleep(1);
                if(g_data == 3){
                        pthread_mutex_unlock(&mutex);
                        printf("t1 quit================\n");
                        pthread_exit(NULL);
                }
        }
}

void* fun2(void *arg)
{
        printf("t2：%ld thread is create\n", (unsigned long)pthread_self());
        printf("t2: %d\n", *((int*)arg));
        while(1){
                printf("t2:%d\n", g_data);
                pthread_mutex_lock(&mutex);
                g_data++;
                pthread_mutex_unlock(&mutex);
                sleep(1);
        }
}

int main()
{

        int ret;
        int param = 100;
        pthread_t t1;
        pthread_t t2;

        pthread_mutex_init(&mutex, NULL);

        //                       线程属性 线程函数 线程函数参数
        ret = pthread_create(&t1, NULL, fun1, (void*)&param);
        if(ret == 0){
                printf("main:create t1 success\n");
        } else {
                perror("why t1 fail");
        }

        ret = pthread_create(&t2, NULL, fun2, (void*)&param);
        if(ret == 0){
                printf("main:create t1 success\n");
        } else {
                perror("why t2 fail");
        }

        printf("main:%ld\n", (unsigned long)pthread_self());//打印主线程ID

        while(1){
                printf("main:%d\n", g_data);
                sleep(1);
        }

        pthread_join(t1, NULL);//等待线程结束，防止进程结束，线程还未执行完毕
        pthread_join(t2, NULL);//等待线程结束，防止进程结束，线程还未执行完毕

        pthread_mutex_destroy(&mutex);
        return 0;
}