C - child processes are displayed in wrong place

Question

I wrote a code in C that takes input argument, creates two child processes by using CreateProcessA(...), but it is not always working as it should. In console it should be displayed like
:

and most of the time it is like that. But sometimes...

this happens (some PIDs are not getting into right "groups"). I tried to fix that in many different ways (my Linux's code using forks(), that does the same, works like a charm by the way), but any change did not fix the problem.
Here is the code:

#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>
#include<string.h>
#include<windows.h>
#include<tchar.h>
#include<process.h>
#include<processthreadsapi.h>

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

    if (argc != 2)
    {
        fprintf(stderr, "Wrong number of input arguments!\n");
        return 1;
    }

    char* endptr;
    int secs = strtol(argv[1], &endptr, 10);
    if (secs <= 0 || *endptr != '\0')
    {
        fprintf(stderr, "Input argument is not a natural number!\n");
        return 2;
    }

    if (atoi(argv[1]) < 1 || atoi(argv[1]) > 13)
    {
        fprintf(stderr, "Input argument must be between 1 and 13\n");
        return 3;
    }

    if (atoi(argv[1]) == 1 || atoi(argv[1]) == 2)
    {
        return 1;
    }
//CreateProcessA() etc part is here

STARTUPINFO si;
PROCESS_INFORMATION pi[2];

memset(&si, 0, sizeof(si));
memset(&pi, 0, sizeof(pi));
si.cb = sizeof(si);

int argument = atoi(argv[1]);   
int argument1 = argument - 1;
int argument2 = argument - 2;

char a1[50];
sprintf(a1, "thisprogram.exe %d", argument1);

BOOL v1 = CreateProcessA("thisprogram.exe", a1, NULL, NULL, 0, 0, NULL, NULL, &si, pi+0);

char a2[50];
sprintf(a2, "thisprogram.exe %d", argument2);

BOOL v2 = CreateProcessA("thisprogram.exe", a2, NULL, NULL, 0, 0, NULL, NULL, &si, pi+1);

WaitForSingleObject(pi[0].hProcess, INFINITE);
WaitForSingleObject(pi[1].hProcess, INFINITE);

DWORD exit1;
GetExitCodeProcess(pi[0].hProcess, &exit1);

DWORD exit2;
GetExitCodeProcess(pi[1].hProcess, &exit2);
    
DWORD pid = GetCurrentProcessId();

printf("%d \t %d \t %d \t %d \t\n", pid, pi[0].dwProcessId, argument1, exit1);
printf("%d \t %d \t %d \t %d \t\n", pid, pi[1].dwProcessId, argument2, exit2);
printf("%d \t \t \t %d\n\n", GetCurrentProcessId(), exit1 + exit2);

for (int i = 0; i >= 0; i--)
{
    CloseHandle(pi[i].hProcess);
    CloseHandle(pi[i].hThread);
}

return exit1+exit2;

}
Shown examples' input argument is 5. For 4 it always work fine. For 6 and more - problem is getting bigger and bigger. I don't think it is a "normal" thing. Any ideas to fix the problem?
Thanks for any help.

I'm trying to solve getting PIDs in wrong place. 3 PIDs should be in the same "group", but as it is shown, sometimes there is group of 2 and that one missing PID from it's orginal group is in another PID's group. (for example: 222 222 222 | 444 444 444 is good, 222 222 444 222 | 444 444 is not) — siwakw7, Dec 16 '20 at 19:46

score 1 · Accepted Answer · answered Dec 16 '20 at 20:37

I don't think it is a "normal" thing.

Actually, it is a normal thing, because they are running concurrently while sharing the same console. In order to fix this, you can do one of these:

You can set CREATE_NEW_CONSOLE flag as stated here. But in this way, you can not display the output in a single window.
You can create a print function and a named mutex object for printing to the console and locking the print function for multiple processes, ordinarily.
Use threads rather than child processes, write a print function, and create an unnamed mutex object to lock print function.

Some related links: first, second.

C - child processes are displayed in wrong place

1 Answers1