Why semaphore object is not initialized? - semaphore

Question

I'm learning to use semaphore object. But I can't initialize it.
A sem_init function always return value -1 rain or shine.
return value -1 indicates first argument is not valid pointer, say my reference.
But I can't find miss print in my code. I compiled my code in Xcode on OS X.
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <pthread.h>
#include <semaphore.h>
void * thread_snd(void *arg);
void * thread_rcv(void* arg);
sem_t bin_sem;
int number = 0;
char thread1[] = "A thread";
char thread2[] = "B thread";
char thread3[] = "C thread";
int main(int argc, char** argv)
{
pthread_t t1, t2 ,t3;
void *thread_result;
int state;
state = sem_init(&bin_sem, 0, 0);
if(state != 0)
{
puts("fail to initialize semaphore");
exit(1);
}
pthread_create(&t1, NULL, thread_snd, &thread1);
pthread_create(&t2, NULL, thread_rcv, &thread2);
pthread_create(&t3, NULL, thread_rcv, &thread3);
pthread_join(t1, &thread_result);
pthread_join(t2, &thread_result);
pthread_join(t3, &thread_result);
printf("final number : %d \n", number);
sem_destroy(&bin_sem);
return 0;
}
void * thread_snd(void * arg)
{
int i;
for(i = 0 ; i < 4; i++)
{
while(number != 0)
sleep(1);
number++;
printf("execution : %s, number : %d \n", (char*) arg, number);
sem_post(&bin_sem);
}
}
void * thread_rcv(void* arg)
{
int i;
for(i = 0 ; i < 2; i++)
{
sem_wait(&bin_sem);
number--;
printf("execution : %s number : %d \n", (char*)arg, number);
}
}

Answer 1

On Mac OS X (10.6.8) there is no sem_init() and sem_destroy().
Use sem_open() and sem_unlink() instead.
/*
cat semaphore_test.c
source:
"Why semaphore object is not initialized?",
https://stackoverflow.com/questions/13834367/why-semaphore-object-is-not-initialized
compiled on Mac OS X 10.6.8 with:
gcc -ansi -pedantic -std=gnu99 -Os -Wall -Wextra -Wshadow -Wpointer-arith -Wcast-qual -Wstrict-prototypes \
-Wmissing-prototypes -Wformat=2 -Wreturn-type -Wunreachable-code -finline -l pthread -o semaphore_test semaphore_test.c
./semaphore_test
*/
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <pthread.h>
#include <semaphore.h>
void * thread_snd(void *arg);
void * thread_rcv(void* arg);
//sem_t bin_sem;
static sem_t *bin_sem;
static const char *semname = "Semaphore";
static int number = 0;
char thread1[] = "A thread";
char thread2[] = "B thread";
char thread3[] = "C thread";
int main(void)
{
pthread_t t1, t2 ,t3;
void *thread_result;
int state;
/*
state = sem_init(&bin_sem, 0, 0);
if(state != 0)
{
puts("fail to initialize semaphore");
exit(1);
}
*/
bin_sem = sem_open(semname, O_CREAT, 0777, 0);
if (bin_sem == SEM_FAILED)
{
fprintf(stderr, "%s\n", "ERROR creating semaphore semname");
exit(EXIT_FAILURE);
}
pthread_create(&t1, NULL, thread_snd, &thread1);
pthread_create(&t2, NULL, thread_rcv, &thread2);
pthread_create(&t3, NULL, thread_rcv, &thread3);
pthread_join(t1, &thread_result);
pthread_join(t2, &thread_result);
pthread_join(t3, &thread_result);
printf("final number : %d \n", number);
//sem_destroy(&bin_sem);
sem_unlink(semname);
return 0;
}
void * thread_snd(void * arg)
{
int i;
for(i = 0 ; i < 4; i++)
{
while(number != 0)
sleep(1);
number++;
printf("snd execution : %s, number : %d \n", (char*) arg, number);
//sem_post(&bin_sem);
sem_post(bin_sem);
}
}
void * thread_rcv(void* arg)
{
int i;
for(i = 0 ; i < 2; i++)
{
//sem_wait(&bin_sem);
sem_wait(bin_sem);
number--;
printf("rcv execution : %s number : %d \n", (char*)arg, number);
}
}
See also:
sem_init on OS X
Program using Semaphores runs fine on Linux... unexpected results on Mac OS X