My fork() never equals 0 - c

Question

I have this code where my fork() never equals 0, so it never executes the code inside my if(pubpid == 0){} statement.
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <wordexp.h>
#define MAX_VAL 256
#define MAX_ENTRIES 1000
pid_t pubpid, subpid, ATPpid;
char *subconnect;
char *pubconnect;
char *subaccept;
char *pub_message[] = {"pub pubid connect", "pub pubid topic 1", "end"};
char *sub_message[] = {"sub subid connect", "sub subid topic 1", "end"};
int main(int argc, char **argv)
{
int i, j, publishers, subscribers, topics;
//Grab input arguments
publishers = atoi(argv[1]); //number of publishers
subscribers = atoi(argv[2]); //number of suscribers
topics = atoi(argv[3]); //number of topics
int ATP_Sub[subscribers][2];
int Sub_ATP[subscribers][2];
int ATP_Pub[publishers][2];
int Pub_ATP[publishers][2];
for(i = 0; i < publishers; i++) //publisher
{
pipe(ATP_Pub[i]);
pipe(Pub_ATP[i]);
}
for(i = 0; i < subscribers; i++) //subscriber
{
pipe(ATP_Sub[i]);
pipe(Sub_ATP[i]);
}
//ATP Server
ATPpid = fork();
if(ATPpid == -1){
perror("fork error\n");
exit(1);
}
if(ATPpid == 0){
for(i = 0; i < publishers; i++){
char buffer1[256];
close(Pub_ATP[i][1]);
read(Pub_ATP[i][0], buffer1, 256);
printf("Publisher Accepted!\n");
close(ATP_Pub[i][0]);
write(ATP_Pub[i][1], "accept", sizeof("accept"));
}
close(Pub_ATP[i][0]);
close(Pub_ATP[i][1]);
for(i = 0; i < subscribers; i++){
char buffer2[256];
close(Sub_ATP[i][1]);
read(Sub_ATP[i][0], buffer2, 256);
close(ATP_Sub[i][0]);
write(ATP_Sub[i][1], "accept", 6);
}
close(Sub_ATP[i][0]);
close(Sub_ATP[i][1]);
}
else{
}
//Publisher Pipes
for(i = 0; i < publishers; i++)
{
pubpid = fork();
if(pubpid < -1)
{
perror("fork error\n");
exit(1);
}
if(pubpid == 0)
{
for(j=0; j < 3; j++)
{
char publisherbuffer[256];
//Write to ATP
close(Pub_ATP[i][0]);
write(Pub_ATP[i][1], pub_message[j], 256);
printf("Publisher Connected!");
//Read from ATP
close(ATP_Pub[i][1]);
read(ATP_Pub[i][0], publisherbuffer, 256);
//Check if accept
while(strcmp(publisherbuffer, "accept") != 0)
{
close(ATP_Pub[i][1]);
read(ATP_Pub[i][0], publisherbuffer, 256);
}
}
close(ATP_Pub[i][1]);
close(ATP_Pub[i][0]);
exit(0);
}
else
{
}
}
//Subscriber Pipes
for(i = 0; i < subscribers; i++)
{
subpid = fork();
if(subpid < -1) {
perror("fork error\n");
exit(1);
}
if(subpid == 0){
printf("hello");
for(j=0; j < 3; j++)
{
char subscriberbuffer[256];
//Write to ATP
close(Sub_ATP[i][0]);
write(Sub_ATP[i][1], sub_message[j], 20);
//Read from ATP
close(ATP_Sub[i][1]);
read(ATP_Sub[i][0], subscriberbuffer, 256);
//Check if accept
while(strcmp(subscriberbuffer, "accept") != 0)
{
close(ATP_Sub[i][1]);
read(ATP_Sub[i][0], subscriberbuffer, 256);
}
}
close(ATP_Sub[i][1]);
close(ATP_Sub[i][0]);
}
else {
}
}
return 0;
}
My ATPpid will equal 0, as proven by my print statement, but I never get into my pubpid :( "Publisher Accepted!" is always printed, but never "Published Connected!"
Thanks in advance!

Answer 1

Well there are too many things to fix up, hard to respond the question without just saying "take a debugger"
1) actually, you first fork's child ends up blocking on:
read(Pub_ATP[i][0], buffer1, 256);
but as the father does not send anything not waits for its child, the program ends.
There is probably a closing brace missing before
//Publisher forks
2) your fathers should always wait for completion or the children
3) cannot really figure out what
for(j=0; j < 3; j++)
is used for (you never use j
The following code is just fixes the points I told you, and get your messages to be displayed (nevertheless, does not fix any other bug)
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char **argv)
{
int i, j, publishers, subscribers, topics;
//Grab input arguments
publishers = atoi(argv[1]); //number of publishers
subscribers = atoi(argv[2]); //number of suscribers
topics = atoi(argv[3]); //number of topics
int ATP_Sub[subscribers][2];
int Sub_ATP[subscribers][2];
int ATP_Pub[publishers][2];
int Pub_ATP[publishers][2];
for(i = 0; i < publishers; i++) //publisher pipes
{
pipe(ATP_Pub[i]);
pipe(Pub_ATP[i]);
}
//ATP Server
int ATPpid = fork();
if(ATPpid == -1){
perror("fork error\n");
exit(1);
}
if(ATPpid == 0){
for(i = 0; i < publishers; i++){
char buffer1[256];
close(Pub_ATP[i][1]);
read(Pub_ATP[i][0], buffer1, 256);
printf("Publisher Accepted %s!\n", buffer1);
close(ATP_Pub[i][0]);
write(ATP_Pub[i][1], "accept", sizeof("accept"));
}
close(Pub_ATP[i][0]);
close(Pub_ATP[i][1]);
exit(0);
}
//Publisher forks
for(i = 0; i < publishers; i++)
{
int pubpid = fork();
if(pubpid == -1)
{
perror("fork error\n");
exit(1);
}
if(pubpid == 0)
{
char publisherbuffer[256];
//Write to ATP
close(Pub_ATP[i][0]);
write(Pub_ATP[i][1], "test", 256);
printf("Publisher Connected!");
//Read from ATP
close(ATP_Pub[i][1]);
read(ATP_Pub[i][0], publisherbuffer, 256);
//Check if accept
while(strcmp(publisherbuffer, "accept") != 0)
{
close(ATP_Pub[i][1]);
read(ATP_Pub[i][0], publisherbuffer, 256);
}
close(ATP_Pub[i][1]);
close(ATP_Pub[i][0]);
exit(0);
}
else
{
waitpid(pubpid, NULL, 0);
}
}
waitpid(ATPpid, NULL, 0);
return 0;
}
you may also notice the children are spawn sequentially, which is probably not what you want, you would need to "save" each child pid in an array to do that.

Answer 2

You have several logical problems. Your Publisher connected message is printed for a bad reason! You create pipes, then fork. In the child you close the write part and are blocked on the read part, in the parent you just terminate, that closes read and write parts, then the child is unblocked in its read because there is no more writer.
You didn't test the returned values; here you would be able to see that it detected an end of file. You also use concurrent reads which is a big problem to solve.
Remember that using pipe need to take precautions. Reading/writing are blocked (by default). reading on empty pipe while no more writer : end of file. writing while no more reader : SIGPIPE, etc. You must verify your reading/writing protocol carfully.
Look at the string lengths, you need to send the NUL terminating C-string to behave correctly.