CODEWITHSUNDEEP
windowsperl
antred
antred

Reputation: 3884

(fork / waitpid) Wait for a list of child processes but interrupt the wait every time a child finishes

I'm using fork to spawn a number of child processes that run several tasks in parallel. In my case it is not sufficient to simply wait on all child processes in a loop, because if the first process in my list is the last to finish then my waitpid call would block until that process has finished.

I want my waitpid call to wake up every time a process has finished. The reason is that I immediately want to inspect the finished child process's exit code to determine if the process was successful so I can cancel any child processes still running. In my case, there is no point in letting them continue (potentially for hours!) if any child process returns a non-zero exit code because that would indicate an error, and even a single error would make the whole undertaking pointless.

(EDIT: I know that that's not how waitpid actually works, but I'm looking for something like that.)

Now, I could do this by using a loop to call waitpid with the WNOHANG flag and then keep checking my child processes with sleep intervals between individual waitpid calls, but this solution seems like a hack. Does anyone have a more elegant solution?

Upvotes: 3

Views: 551

Answers (2)

Pradeep
Pradeep

Reputation: 3153

You can trap SIGCHLD, something like this:

$SIG{CHLD} = sub {
    my $child;
    while ( ( $child = waitpid( -1, WNOHANG ) ) > 0 ) {
        warn("Reaped $child, exited with $?");
    }
};

Upvotes: 2

Miguel Prz
Miguel Prz

Reputation: 13792

You can use the wait function, it waits for a child process to terminate and returns the pid of the deceased process.

Upvotes: 3

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