michaelfung has asked for the wisdom of the Perl Monks concerning the following question:

Dear Monks,

I need to handle thousands of concurrent TCP connections. I use AnyEvent/EV. In order to take advantage of multiple CPUs, I pre-forked some children and pass them client socket handles. I pass the handles with AnyEvent::Beanstalk, when the child receives it, it complains it is not an AnyEvent Handle. I tried to use Storable to serialize the handle before passing but to no avail.

So, is this pre-fork approach practical at all with perl?

  • Comment on How to pass AnyEvent socket handle to pre-forked child process?

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Re: How to pass AnyEvent socket handle to pre-forked child process?
by zwon (Abbot) on Jan 21, 2013 at 12:05 UTC

    You can't pass filehandles between processes. Instead just let children accept connections.

[reply]

      Actually, you can pass filehandles between processes, it's just not something that solves many problems, and there usually are better ways to accomplish the same, as you outlined already. :-)

      PPerl has code for passing around filehandles in pass_fd.c, and I wrote a replacement for that for Win32, but can't find it on RT. Maybe I forgot to open a bug for it.

      This approach still leaves systems not so close to Unix in the rain of course, so your better, and common, approach of using accept still stands.

[reply]
        That's interesting, probably it's time to reread APUE, thank you
[reply]

      I can't use accept() as it is not accessible in AnyEvent.

[reply]

        If whatever you receive actually is a filehandle, or even better, a socket, then you need to maybe wrap it with an AnyEvent::Handle. Looking at AnyEvent::Beanstalk, I don't see how to pass sockets around with it though.

[reply]

        You can use accept, you just should ensure that it will not block. Make server socket non-blocking, add read watcher to it, in read callback accept all connections. Something like: 

        use AnyEvent::Util qw(fh_nonblocking);
...;
fh_nonblocking $srv_sock, 1;
my $w = AE::io $srv_sock, 0, sub {
    while(accept my $cli_sock, $srv_sock) {
        # initialize watchers for client socket
    }
};

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