From C++, I wish to submit a process, pause, resume it and stop it. For this, I am first using the following function to run a shell process in the background and save the associate PID. I found the function at this post (and only removed the standard input and output).
int system2(const char * command)
{
int p_stdin[2];
int p_stdout[2];
int pid;
if (pipe(p_stdin) == -1)
return -1;
if (pipe(p_stdout) == -1) {
close(p_stdin[0]);
close(p_stdin[1]);
return -1;
}
pid = fork();
if (pid < 0) {
close(p_stdin[0]);
close(p_stdin[1]);
close(p_stdout[0]);
close(p_stdout[1]);
return pid;
} else if (pid == 0) {
close(p_stdin[1]);
dup2(p_stdin[0], 0);
close(p_stdout[0]);
dup2(p_stdout[1], 1);
dup2(::open("/dev/null", O_RDONLY), 2);
/// Close all other descriptors for the safety sake.
for (int i = 3; i < 4096; ++i)
::close(i);
setsid();
execl("/bin/sh", "sh", "-c", command, NULL);
_exit(1);
}
close(p_stdin[0]);
close(p_stdout[1]);
return pid;
}
Then, I am using the kill function, to pause, resume and stop the process but it does not work as I expected. Here is an example:
int main()
{
// The process prints on file allowing me to figure out whether the process is paused / stopped, or is running
const char * command = "for i in {1..1000}; do echo $i >> /Users/remi/test/data.txt; sleep 1s;done";
// Run the command and record pid
auto pid = system2(command);
std::cout << "pid = " << pid << "\n";
// with this pid, I could ensure that `ps -p <pid>` returns the correct command
std::cout << "process should be running!\n"; // It is!
// wait
std::this_thread::sleep_for(std::chrono::seconds(10));
// pause
kill(pid, SIGTSTP);
std::cout << "process should be paused!\n"; // But it is not!
// wait
std::this_thread::sleep_for(std::chrono::seconds(10));
// resume process
kill(pid, SIGCONT);
std::cout << "process should be running!\n"; // Sure, it is as it has never been stopped
// wait
std::this_thread::sleep_for(std::chrono::seconds(10));
// Kill process
kill(pid, SIGSTOP);
std::cout << "process should be stopped!\n"; // That worked!
// wait
std::this_thread::sleep_for(std::chrono::seconds(10));
}
Can you please help me figure out how to fix this code to ensure the process stops and resume as I was expected.
FYI, I am on a macOS and wish the solution work on any POSIX system.
