Re: gethostbyname and Event

On Sun, Sep 09, 2001 at 09:08:12AM -0700, [email protected] wrote:
> well-understood.  The 'standard' solution (employed by netscape and
> squid among others) is to fork one or more 'helper' processes.  The

This is actually what the Coro module does (Coro::Util::gethostbyname),
albeit very suboptimal (one fork for every resolve, but that could be
transparently improved).

> - has anyone done this already?  Someone else must have
> encountered this problem before.  Are there pre-existing solutions?

The drawback is that Coro does not work with callbacks and just blocks the
calling coroutine ;->

Anyway, if you don't call gethostbyname in a tight loop, it's fairly
trivial to implement a seperate process solution. My (suboptimal) one
looks like this (obviously one would have to modify it to use a callback
instead of using the "unblock" call.

sub _do_asy(&;@) {
   require POSIX; # just for _exit

   my $sub = shift;
   $jobs->down; # semaphore to limit max. number of parallel jobs
   my $fh;
   if (0 == open $fh, "-|") {
      syswrite STDOUT, join "\0", map { unpack "H*", $_ } &$sub;
      POSIX::_exit(0);
   }
   my $buf;
   $fh = unblock $fh;
   $fh->read($buf, 16384);
   close $fh;
   $jobs->up; # semaphore to limit max. number of parallel jobs
   my @r = map { pack "H*", $_ } split /\0/, $buf;
   wantarray ? @r : $r[0];
}

=item gethostbyname, gethostbyaddr

Work exactly like their perl counterparts, but do not block. Currently
this is being implemented by forking, so it's not exactly low-cost.

=cut

sub gethostbyname($) {
   _do_asy { gethostbyname $_[0] } @_;
}

sub gethostbyaddr($$) {
   _do_asy { gethostbyaddr $_[0], $_[1] } @_;
}


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