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Child Process Executing Print Statement But Nothing Afterwards


Child Process Executing Print Statement But Nothing Afterwards

By : Saran Solutions
Date : September 23 2020, 05:00 AM
it should still fix some issue I have the following code: , When you do :
code :
dup2(fd[1], STDOUT_FILENO)
//dup2(fd[1], STDOUT_FILENO)


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How to create two child process executing parallel from a single parent process in C++?

How to create two child process executing parallel from a single parent process in C++?


By : mckbgrd
Date : March 29 2020, 07:55 AM
it should still fix some issue use fork() and exec family of functions to start child processes. parent process can call waitpid till child process exists.
exec link: http://linux.about.com/library/cmd/blcmdl3_execvp.htm
Can a CPU keep a process in pending state for 10 seconds, while a child process is executing?

Can a CPU keep a process in pending state for 10 seconds, while a child process is executing?


By : Maddin Oltschbee
Date : March 29 2020, 07:55 AM
it helps some times It is in theory POSSIBLE that the parent process is blocked for 10 seconds [not by the CPU as such, but by the OS scheduling mechanism]. But since the forked process is at the same priority as the parent in this case, it's quite unlikely that the child process gets to run before the parent completes, but like any two unsynchronized processes, it's impossible to entirely guarantee which order they execute in.
On my machine, certainly, the child process doesn't run until well after the parent process has completed. So output is:
code :
Parent process 
[my prompt $] Child Process
C - Child Process Not Executing

C - Child Process Not Executing


By : Michael Bondo Anders
Date : March 29 2020, 07:55 AM
wish helps you Here is a suggestion, check for child_pid == 0 explicitly cause it could also be the case that your safe_fork() function failed, also check for those errors i.e child_pid < 0. Add debug printf statements to check control flow if you already haven't and finally check if the execl call failed.
Also please have a look at this tutorial for creating pipes in C and using them to communicate between a parent and a child process. As I feel there are some issues with how you are handling those file descriptors. A possible reason that you can't see any output is that wc might still waiting for some input.
Why does the child process executing uniq -d not print duplicates passed by pipe over stdin?

Why does the child process executing uniq -d not print duplicates passed by pipe over stdin?


By : perfectstorms
Date : March 29 2020, 07:55 AM
help you fix your problem You have to close the pipe before waiting for uniq to finish, because it won't know it's got EOF until you close the pipe. And you've not written even one line to the standard input of uniq because there isn't a newline in the data that was written. The write() system call writes only what you tell it to write; it certainly doesn't add any newlines of its own volition.
Those changes, and sundry trivia, lead to:
code :
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <unistd.h>

int main(void)
{
    int pipefd[2];
    if (pipe(pipefd) < 0)
    {
        fprintf(stderr, "Failed to create pipe\n");
        return 1;
    }

    char *argv[] = {"uniq", "-d", (char *)0};

    pid_t pid = fork();

    switch (pid)
    {
    case -1:
        fprintf(stderr, "Failed to fork\n");
        return 1;

    case 0:
        close(pipefd[1]);
        dup2(pipefd[0], STDIN_FILENO);
        close(pipefd[0]);
        execvp(argv[0], argv);
        fprintf(stderr, "Failed to exec %s\n", argv[0]);
        exit(errno);

    default:
        close(pipefd[0]);
        write(pipefd[1], "test1\n", 6);
        write(pipefd[1], "test1\n", 6);
        write(pipefd[1], "test2\n", 6);
        close(pipefd[1]);
        int status;
        int corpse = wait(&status);

        if (WEXITSTATUS(status) != EXIT_SUCCESS)
        {
            fprintf(stderr, "Child (%s) exited (PID %d, status 0x%.4X)\n", argv[0], corpse, status);
        }
        break;
    }
    return 0;
}
How to print output of an interactive child process from parent process?

How to print output of an interactive child process from parent process?


By : Jonathan
Date : March 29 2020, 07:55 AM
Hope that helps Run exec.Command("python", "-i").
By default when running python not in a shell it won't enter interactive mode and won't print anything out.
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