Dear friends,
I want to extend the interrupt handler of a program, my code is: -
...
-
if ($pid = fork) {
-
local $SIG{INT} = sub {
-
print "Please select:\n";
-
$choice = <STDIN>;
-
if ($choice eq "a") {
-
&sub_routine();
-
}
-
else {
-
kill INT => $pid; # send signal to child by parent selectively
-
}
-
};
-
}
-
else {
-
exec("origninal.pl"); # original program, have its own INT handler
-
...
-
}
-
But when I hit ctrl+c, both parent and child process receive INT, the
choice doesn't work.
How can I make child process only accept signal from parent?
Thanks a lot!
3  2283  miller 1,089
Recognized Expert Top Contributor
Greetings Joel,
I'm not a fork expert, nor do I have a lot of experience working with signals. However there are a couple obvious bugs in your problem.
First off, the INT handler that you created for the parent process will never actually be used. Use rightly use local in that assignment, but that is all you do in the parent if statement. This means $SIG{INT} handler is reverted back to it's original value immediately after the assignment because the if block is left. Most likely you need a wait command, but this is the point where my ipc knowledge becomes only perfunctory.
Also, your test for your choice will never match because you do not chomp $choice.
There are other improvements that I would advise, but I'll leave it there for now.
- Miller
Dear Miller and other friends, Thank you for the work that made my question clear, also I find that
you are very precise. One of the improvments you mentioned might be checking whether
fork is successful, to make this piece of code not pseudo-code like,
I will add it.
Seems the original post can't be modified :-(
-Joe
miller 1,089
Recognized Expert Top Contributor
Hello Joel,
Yes, fork and process programming is definitely one of those areas where it is in your best interest to never skimp on error checking. You should definitely add the check for if $pid is defined. As that is the first thing that I would do if I was to refactor your code.
Anyway, good luck with your project, and feel free to ask further questions if you hit a block again.
- Miller
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