LinuxQuestions.org - IPC - semphores and static functions

In the book "Beginning Linux Programming [Wrox Press]" there's an example about IPC semaphores. It implements the simplest form of a semaphore (a binary semaphore) by a set of 4 functions. Alle of these functions are "static". Anybody knows why they are static functions? Do they need to be static? Why (not)?

Code:

/* Taken from the book "Beginning Linux Programming" by Wrox Press

 * released under GPL by Wrox

 */



#include <unistd.h>

#include <stdlib.h>

#include <stdio.h>



#include <sys/types.h>

#include <sys/ipc.h>

#include <sys/sem.h>



static int set_semvalue(void);

static void del_semvalue(void);

static int semaphore_p(void);

static int semaphore_v(void);



static int sem_id;





int main(int argc, char *argv[])

{

    int i;

    int pause_time;

    char op_char = 'O';



    srand((unsigned int)getpid());

    

    sem_id = semget((key_t)1234, 1, 0666 | IPC_CREAT);



    if (argc > 1) {

        if (!set_semvalue()) {

            fprintf(stderr, "Failed to initialize semaphore\n");

            exit(EXIT_FAILURE);

        }

        op_char = 'X';

        sleep(2);

    }

    

    for(i = 0; i < 10; i++) {        



        if (!semaphore_p()) exit(EXIT_FAILURE);



            /* start of critical section */

        printf("%c", op_char);fflush(stdout);

        pause_time = rand() % 3;

        sleep(pause_time);

        printf("%c", op_char);fflush(stdout);

            /* end of critical section */        



        if (!semaphore_v()) exit(EXIT_FAILURE);

        

        pause_time = rand() % 2;

        sleep(pause_time);

    }    



    printf("\n%d - finished\n", getpid());



    if (argc > 1) {    

        sleep(10);

        del_semvalue();

    }

        

    exit(EXIT_SUCCESS);

}



static int set_semvalue(void)

{

    union semun sem_union;



    sem_union.val = 1;

    if (semctl(sem_id, 0, SETVAL, sem_union) == -1) return(0);

    return(1);

}



static void del_semvalue(void)

{

    union semun sem_union;

    

    if (semctl(sem_id, 0, IPC_RMID, sem_union) == -1)

        fprintf(stderr, "Failed to delete semaphore\n");

}



static int semaphore_p(void)

{

    struct sembuf sem_b;

    

    sem_b.sem_num = 0;

    sem_b.sem_op = -1; /* P() */

    sem_b.sem_flg = SEM_UNDO;

    if (semop(sem_id, &sem_b, 1) == -1) {

        fprintf(stderr, "semaphore_p failed\n");

        return(0);

    }

    return(1);

}



static int semaphore_v(void)

{

    struct sembuf sem_b;

    

    sem_b.sem_num = 0;

    sem_b.sem_op = 1; /* V() */

    sem_b.sem_flg = SEM_UNDO;

    if (semop(sem_id, &sem_b, 1) == -1) {

        fprintf(stderr, "semaphore_v failed\n");

        return(0);

    }

    return(1);

}