POSIX信号量实现互斥

来源：互联网发布：三峡大学网络课程编辑：程序博客网时间：2024/06/05 18:46
采用POSIX信号量实现互斥原语，实现线程间同步
/* * 采用信号量实现互斥原语 */#include <stdio.h>#include <stdlib.h>#include <semaphore.h>#include <unistd.h>#include <errno.h>#include <limits.h>#include <sys/types.h>#include <fcntl.h>#include <pthread.h>#define MAXNUM 10000//用一个结构体封装命名信号量struct slock{    sem_t* pSem;    char name[_POSIX_NAME_MAX];};//为信号量结构体分配内存struct slock* s_alloc(){    struct slock* sp;    static int cnt;    if((sp = (struct slock*)malloc(sizeof(struct slock))) == NULL)        return NULL;    do    {        snprintf(sp->name, sizeof(sp->name), "/%ld.%d", (long)getpid(), cnt++);        sp->pSem = sem_open(sp->name, O_CREAT|O_EXCL, S_IRWXU, 1);    }    while((sp->pSem == SEM_FAILED) && (errno == EEXIST));    if(sp->pSem == SEM_FAILED)    {        free(sp);        return NULL;    }    sem_unlink(sp->name);    return sp;}//释放内存void s_free(struct slock* sp){    if(sp != NULL)    {        sem_close(sp->pSem);        free(sp);        sp = NULL;    }}//互斥lockint s_lock(struct slock* sp){    return sem_wait(sp->pSem);}//互斥unlockint s_unlock(struct slock* sp){    return sem_post(sp->pSem);}//互斥trylockint s_trylock(struct slock* sp){    return sem_trywait(sp->pSem);}//线程函数static void* th_fun1(void* pArg);static void* th_fun2(void* pArg);//封装结构体作为参数传给线程struct foo{    int count;    struct slock* pslock;};int main(){    int err;    pthread_t tid1, tid2;    struct foo obj;    obj.count = 0;    if((obj.pslock = s_alloc()) == NULL)        return 0;    //创建线程    err = pthread_create(&tid1, NULL, th_fun1, (void*)&obj);    if(err != 0)    {        perror("pthread_create error");        exit(1);    }    err = pthread_create(&tid2, NULL, th_fun2, (void*)&obj);    if(err != 0)    {        perror("pthread_create error");        exit(1);    }    //在主线程中等待线程退出    pthread_join(tid1, NULL);    printf("thread 1 exit\n");    pthread_join(tid2, NULL);    printf("thread 2 exit\n");    s_free(obj.pslock);    exit(0);}static void* th_fun1(void* pArg){    while(1)    {        struct foo* pObj = (struct foo*)pArg;        s_lock(pObj->pslock);        if(pObj->count == MAXNUM)        {            s_unlock(pObj->pslock);            break;        }        pObj->count++;        printf("thread 1 print count: %d\n", pObj->count);        s_unlock(pObj->pslock);    }    return ((void*)1);}static void* th_fun2(void* pArg){    while(1)    {        struct foo* pObj = (struct foo*)pArg;        s_lock(pObj->pslock);        if(pObj->count == MAXNUM)        {            s_unlock(pObj->pslock);            break;        }        pObj->count++;        printf("thread 2 print count: %d\n", pObj->count);        s_unlock(pObj->pslock);    }    return ((void*)2);}
参考：APUE第三版第15章
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