OS X semaphore irregularities

[Computer Guru]

Hi all,

I have some very basic semaphore code that works great on Linux, but cannot for the life of me get it to run properly on OS X... It returns the oddest of results...

#include <iostream>
#include <fcntl.h>
#include <stdio.h>
#include <semaphore.h>

int main()
{
	sem_t* test;
	test = sem_open("test", O_CREAT, 0, 1);
	
	int value;
	sem_getvalue(test, &value);
	printf("Semaphore initialized to %d\n", value);
}

Compiling this on OS X with g++ returns the following output:

iQudsi:Desktop mqudsi$ g++ test.cpp
iQudsi:Desktop mqudsi$ ./a.out 
Semaphore initialized to -1881139893

Whereas on Ubuntu, I get the decidedly more-sane result:

iQudsi: Desktop mqudsi$ g++ test.cpp -lrt
iQudsi:Desktop mqudsi$ ./a.out 
Semaphore initialized to 1

I've been at this for 3 hours straight, and cannot figure out why OS X is returning such bizarre results...

I've tried using file paths as the semaphore name, it didn't make a difference.

[hayne]

Try instead this program (which checks for errors):

#include <iostream>
#include <fcntl.h>
#include <stdio.h>
#include <semaphore.h>

int main()
{
	sem_t* test;
	test = sem_open("test", O_CREAT, 0, 1);
        if (test == SEM_FAILED)
        {
            perror("sem_open");
        }
	
	int value;
	if (sem_getvalue(test, &value) != 0)
        {
            perror("sem_getvalue");
        }
	printf("Semaphore initialized to %d\n", value);
        return 0;
}

[Computer Guru]

Thanks.

It turns out (despite how much ADC talks about it) sem_getvalue is not implemented on OS X.