I would like to catch signal sent to my program and do simple action (e.g. exit with specified code). But if process received a signal before my signal handler set, it exited abnormally like no handler existed.
Source code of my simple program:
#include <signal.h>
#include <stdlib.h>
#include <unistd.h>
void handler(int sig) { exit(0); }
int main()
{
signal(SIGTERM, handler);
while(1) { sleep(1); }
return 0;
}
Compiled with g++ my.c command.
Script to run program continuously:
while true; do ./a.out; echo $?; done
If I manually send a signal to process then most of time everything is ok - exited with zero code. But if I use script below:
Script for frequent sending signal to process:
while true; do slay -sSIGTERM a.out; done
I've got many of Terminated 143 messages.
But if I use gcc (instead of g++) I could not get the situation with a non-zero exit code.
In this regard, the question of how do I get a C++ (g++ compiled) program similar behavior with the C (gcc compiled) program?
Preferably in the maximum standardized approach.
Tested on QNX 6.5, gcc 4.7.2
The only way to achieve what you want is to have the parent process block all signals (sigprocmask) before forking and wait to unblock them until after setting up your signal handlers. Anything purely in your own program would be useless since the signal could still arrive between the window where the parent forks and where it execs.