How can I resume a stopped process? - c++

Question

Following this documentation, I am testing how to stop and resume a process. I have basic code to test as follows:
#include <iostream>
#include <csignal>
#include <unistd.h>
int main() {
std::cout << "Hello" << std::endl;
int pid = getpid();
kill(pid, SIGSTOP);
kill(pid, SIGCONT);
std::cout << "Bye" << std::endl;
return 0;
}
The output is:
Hello
It stops the process, but it never resumes it. How should I fix it?

Answer 1

A solution, if a bit complicated, is to create a child process to start and stop the parent. Here is a small code example, that might help:
#include <iostream>
#include <csignal>
#include <unistd.h>
int pid; //Include declaration outside so it transfers to the child process
int main() {
std::cout << "Hello" << std::endl;
pid = getpid();
int returned_pid = fork(); //Duplicate process into 2 identical processes
if(returned_pid) {
// If it is the parent process, then fork returns the child process pid
// This is executed by the parent process
usleep(1000); // Sleep a millisecond to allow for the stop command to run
} else {
// If fork returns 0, then it is the child process
// The else is executed by the child process
kill(pid, SIGSTOP); // Stop parent process
usleep(3000000); // Delay 3 seconds
kill(pid, SIGCONT); // Resume parent process
}
if(returned_pid) { // Only print if parent process
std::cout << "Bye" << std::endl;
}
return 0;
}
Clarification: The fork command returns 2 different values in the 2 processes: 0 in the child, and the pid of the child process in the parent.
Other note: When running this in a terminal, it will look weird, as the terminal may note that the process was stopped and give a new command line, but then the process resumes, so prints Bye over it. Just a note.