c - 查找一个进程一次可以打开的最大信号量

为了找到一个进程一次可以打开的最大信号量，我不明白为什么下面的代码_SC_SEM_NSEMS_MAX返回-1。

int main(void) {
        long max_limit = 0;
        errno = EINVAL;
        max_limit = sysconf(_SC_SEM_NSEMS_MAX);
        printf("max_limit : %ld error_no : %d\n",max_limit,errno);

        return 0;
}

编辑：-以下是我试图手动获取的最大限制。

struct count {
        sem_t sem_addr;
        int count;
};
int main(void) {
        int fd = 0,zero = 0;
        struct count *shared;
        fd = shm_open("/my_semaphore",O_RDWR|O_CREAT,0777);
        if(fd == -1){
                perror("shm_open");
                exit(0);
        }
        //ftruncate(fd,4096);
        write(fd,&zero,4);
        shared = mmap(NULL,4096,PROT_READ|PROT_WRITE,MAP_SHARED,fd,(off_t)0);
        sem_init(&shared->sem_addr,1,1);

        pid_t pid = fork();
        if(pid > 0) {
                //printf("parent process: %d \n",getpid());
                sem_wait(&shared->sem_addr);
                for(int i = 0;i < 50 ;i++) {
                        printf("parent = %d \n",shared->count++);
                }
                sem_post(&shared->sem_addr);
        }
        else if (pid == 0) {
                //printf("child process: %d \n",getpid());
                sem_wait(&shared->sem_addr);
                for(int i = 0;i < 50 ;i++) {
                        printf("child = %d \n",shared->count++);
                }
                sem_post(&shared->sem_addr);
        }
        sem_destroy(&shared->sem_addr);
        return 0;
}

任何帮助都将不胜感激。

最佳答案

从手册页：

RETURN VALUE
       If name is invalid, -1 is returned, and errno is set to EINVAL.  Other‐
       wise, the value returned is the value of the system resource and errno
       is  not  changed.  In the case of options, a positive value is returned
       if a queried option is available, and -1 if it is not.  In the case  of
       limits, -1 means that there is no definite limit.

特别注意最后一句话。所以，-1可能意味着你的系统不知道_SC_SEM_NSEMS_MAX或者没有限制。无论哪种方式，我解释这意味着开放信号量的最大数目不是由系统任意限制的（当然它可能受内存限制等限制）。

关于c - 查找一个进程一次可以打开的最大信号量，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/50106374/