process_synchro_semaphores.c

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

#define INFOFUNC printf("[%d] %s\n", getpid(), __FUNCTION__)
#define INFO(m) printf("[%d] %s\n", getpid(), m)

sem_t* parent_sem;
sem_t* sem;

void process1_launch() {
    INFOFUNC;
    INFO("Waiting for proc2");
    sem_wait(sem); // wait for process 2
    INFO("Released proc2");
    INFO("Sending post to parent");
    sem_post(parent_sem);
    INFO("Post to parent sent");
}

void process2_launch() {
    INFOFUNC;
    INFO("Proc2 sleep");
    sleep(3);
    INFO("Proc2 wake up");
    sem_post(sem);
    INFO("Released semafore");
}

#define SEMNAME1 "/sem1111"
#define SEMNAME2 "/sem2222"
int main() {
    // create semaphore
    sem = sem_open(SEMNAME1, O_CREAT | O_EXCL, 0644, 0);
    sem_unlink(SEMNAME1);

    parent_sem = sem_open(SEMNAME2, O_CREAT | O_EXCL, 0644, 0);
    sem_unlink(SEMNAME2);

    printf("parent, sem=%p, parent_sem=%p\n", sem, parent_sem);
    
    pid_t f1 = fork();
    if (f1 == 0) {
        printf("child1, sem=%p, parent_sem=%p\n", sem, parent_sem);
        process1_launch();
        INFO("ending");
        return 0; // child dont go further
    }

    pid_t f2 = fork();
    if (f2 == 0) {
        printf("child2, sem=%p, parent_sem=%p\n", sem, parent_sem);
        process2_launch();
        INFO("ending");
        return 0; // child dont go furter
    }
    // parent wait for proc1 end
    INFO("Parent wait");
    sem_wait(parent_sem);
    INFO("Parent ending");
    
    printf("parent, sem=%p, parent_sem=%p\n", sem, parent_sem);
    printf("close sem=%d\n", sem_close(sem));
    printf("close parentsem=%d\n", sem_close(parent_sem));
}