Wait for children to complete if parent intercepts SIGINT

问题

I have a perl script with multiple child processes (created using fork()). Each child sleeps then does some processing (several system() calls). Under windows when I hit Ctrl+C I see that the signal was caught , then the script waits for the children to complete and after this exits. I want to replicate this behaviour in linux (catch sigint , let the children complete and exit the main script/process ).

How do I wait for all children to complete before killing the parent ? Is it possible to exit the main script / kill the parent , but let the children complete in the background ?

I found Child process receives parent's SIGINT , and it seems SIGINT is propagated to the children (the process group) , so to avoid this I'd have to set the child in a different process group.

$SIG{'INT'} = sub {
    print "Caught Ctrl+C\n";
    die "Stopping...";
};

++$|;

print "Start\n";
for($i=0; $i < 500; $i++) {
    sleep 3;
    $childPid = fork(); #fork a process
    if($childPid == 0){
        print "Child $i...\n";
        sleep 10;
        system("echo finishing");
        print "Exit child $i\n";
        exit;
    }
}

I also tried to include this in the SIGINT processing block , but the for loop isn't paused , so new child processes are created and parent doesn't die.

# I used my $parentPid = $$; (before  the for loop) to get the parent pid.

if ($$ = $parentPid){
    foreach $var (@pids) {
        $pid = waitpid($var ,0);
    }

EDIT:

Tried setting the child SIGINT handler to IGNORE and it works as expected. In the parent handler I do :

$SIG{'INT'} = sub {
  print "Caught Ctrl+C by $$\n";
  # while($result != -1){
      # $result = wait();
  #}
    die "Stopping...";
};

a) If include the commented lines the script waits for the children to complete and then exits.

b) But if I comment the "wait" lines I assume it works like this

the script exits and the parent process is terminated
the children continue running in the background and display "Exit child" message as expected before exiting.

I understand the a) case but how does the b) case work, please explain why doesn't this generate zombie processes ?

回答1:

Under windows when I hit Ctrl+C I see that the signal was caught , then the script waits for the children to complete and after this exits.

I think this is a side-effect of the psuedo-fork implementation.

How do I wait for all children to complete before killing the parent ?

The easiest way is to ignore the SIGINT In the children, and wait/waitpid in the parents SIGINT handler.

I also tried to include this in the SIGINT processing block , but the for loop isn't paused , so new child processes are created and parent doesn't die.

I think you meant $$ == $parentPid (comparison instead of assignment). Also, it's not really useful to specify which child you're waiting for if you're waiting for all of them anyway.

来源：https://stackoverflow.com/questions/33518868/wait-for-children-to-complete-if-parent-intercepts-sigint

标签

perl

fork