Convert Pthread to process fork()

Question

With this basic pthread code below, what is the method to convert pthread_create to fork() and achieve a similar outcome.

#include <stdio.h>
#include <pthread.h>
#include <semaphore.h> 
#include <unistd.h>
sem_t mutex; 
void* wait_t(void* a)
{
    (int)a--;
    if ((int)a < 0)
    {
        sem_wait(&mutex);
        printf("waiting\n");
    }
}
void* signal_t(void* a)
{
    (int)a++;
    if ((int)a <= 0)
    {
        printf("signal\n");
        sem_post(&mutex);
    }
}
int main()
{
    sem_init(&mutex, 0, 1);
    int i = -2;
    pthread_t t1, t2; 
    pthread_create(&t1, NULL, wait_t, i);
    pthread_create(&t2, NULL, signal_t, i); 
    pthread_join(t1, NULL);
    pthread_join(t2, NULL);
    exit(0); 
}

Possible duplicate of https://stackoverflow.com/questions/10909011/how-to-use-fork-to-create-only-2-child-processes — peachykeen, May 03 '20 at 13:58
You have to create two child processes with `fork()` and in each child process you invoke the functions `wait_t`and `signal_t`. — CRM, May 03 '20 at 13:59
@peachykeen that question is about how to use `fork()` this question convert pthread to process and achieve a similar outcome — Zam-Oxy, May 03 '20 at 14:01

CRM · Accepted Answer · 2020-05-03T14:24:15.937

Unless I'm missing something, the following code allows you to achieve the same functionality using processes instead of threads.

#include <stdio.h>
#include <semaphore.h> 
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/wait.h>

sem_t mutex; 
void wait_t(int a)
{
    a--;
    if (a < 0)
    {
        sem_wait(&mutex);
        printf("waiting\n");
    }
}

void signal_t(int a)
{
    a++;
    if (a <= 0)
    {
        printf("signal\n");
        sem_post(&mutex);
    }
}

int main()
{
    sem_init(&mutex, 0, 1);
    int i = -2;

    if(fork() == 0){ // create 1st child process
        wait_t(i);
        exit(0);
    }

    if(fork() == 0){ // create 2nd child process
        signal_t(i);
        exit(0);
    }


    wait(NULL);
    wait(NULL);

    exit(0); 
}

Note: I'm not validating any possible errors thrown by fork() as it is advisable to do.

You can use it if you want, but in your original example you were not using this information so I didn't use it in the answer. You can get the PID for each process using `getpid()`, and the parent of each process can get this value via `fork()` which, in case of success, returns the PID of the just created child process. — CRM, May 07 '20 at 07:57

Convert Pthread to process fork()

1 Answers1