What is the smart way for start parallel tasks in forked proccess via perl, linux and anyevent?

Question

I have an issue with AnyEvent::Utils::fork_call. I m using fork_call, then doing some work, and after that i should end my fork_call, and start new parallel task.

I tried that:

fork_call {

    # very important work

    # start new parallel task
    if (my $pid = fork) {
        # other important and very long work
    }
} sub {
    # never reached this, while parallel task working
}

I suppouse that any event fork_call is waiting for all its childs to finish their jobs.

So how can I avoid this problem? Maybe I should get rid of parent process?

Any suggestions and advices are welcome. Thank you.

score 2 · Answer 1 · answered May 21 '13 at 13:15

2

I don't know if that suits your needs, but you can run next fork_call in a callback in first one. Something like this appears to work:

fork_call {
    # Important work
} sub {
    fork_call {
        # other important work
    } sub {
        warn "done!";
    }
};

Because second fork_call is used in first one's callback this means it forks and starts after "Important work" is done.

answered May 21 '13 at 13:15

bjakubski

1,477
10
9

Thanks for answer! Suddenly, I can't change code in parent fork_call directly. Parent fork_call was written by another man, it call some other functions, and one of this 'some other' function i should write. Currenly I do some kind of hacking: i do fork (*), then fork (**), and after that stop (*) proccess. I don't think that it is good practice, but it works. Therefore question is still open: how to start parallel task, that not tied to parent fork_call? Or does it possible at all without such kind of hacking? – rasmikun May 21 '13 at 13:30

score 1 · Answer 2 · answered Dec 29 '13 at 00:31

While not directly an answer to your question, doing any nontrivial amounts of processing in a forked child is error-prone and unportable. A generic way to avoid any and all such problems is to use AnyEvent::Fork (and/or AnyEvent::Fork::RPC, AnyEvent::Fork::Pool) to create worker processes. These modules create a new Perl process from scratch and use it to fork further worker processes. This avoids almost all problems with inheriting state from your parent, which might be the problem you are running into - it might especially explain why it works sometimes for you and sometimes not, depending on what other things were going on when the process was forked.

What is the smart way for start parallel tasks in forked proccess via perl, linux and anyevent?

2 Answers2