C ++ Macs OS X semaphore.h：出现“ sem_open（）”和“ sem_wait（）”问题

Question

#include <semaphore.h>

sem_t* x;

int main () 
{
    x = sem_open("x", O_CREAT, 0, 0);;
    sem_wait(x); sem_wait(x); sem_wait(x);
    std::cout << "\ndone\n";
}

This code shouldn't even pass the first sem_wait() but on my system it reaches the end of main() . Everything I have read, such as here and here , say that, although Mac OS X does not support sem_init() , it does support sem_open() . However, using sem_open() as above hasn't fixed the problem. I'm running OS X 10.5.7.

Answer 1

Try putting sem_unlink("x"); before sem_open() , I'm sure it's not your first attempt on it. And mode of 0 won't let you do much with it, unless you remove it. Also, do check your calls for errors, it will if not resolve, but, at least, amend your questions.

Answer 2

Permissions of 0 to sem_open mean that nobody can access the semaphore. You really should add proper error checking -- it will tell you which function is failing and way.