Stupid IO::select question

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

Here's the thing...

I've got a socket, created with IO::Socket::INET, that I've registered with an IO::select object.

I'm writing to the socket using the following code:

if (my @s = $select->can_write()) {
  for (@s) {
    if (print $_ $message) {
       print "message sent";
    } else {
       print STDERR "Could not write to socket: $!\n";
    }
  }
}
[download]

I only have one socket registered with the select, so it only writes to the one socket. This code works fine, except...

The server I'm talking to has the annoying habit of terminating the connection with no warning. When that happens, the $select->can_write() is not blocking, but immediately returns the one registered socket (which was closed from the other end), and the print fails.

Is can_write() supposed to return a handle that I clearly cannot write to? If so, what suggestions can I get for bulletproofing my code?

Comment on Stupid IO::select question Select or Download Code

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Re: Stupid IO::select question by ferrency (Deacon) on Aug 03, 2000 at 21:42 UTC
Disclaimer: I haven't actually tried this. But, you might want to try a has_exception() call to see if there's an error condition on the socket(s) before printing to it (them). Alan	[reply]
Re: Stupid IO::select question by tye (Sage) on Aug 04, 2000 at 08:29 UTC
It almost makes sense. `select` is supposed to tell you when a call won't block. Having the write fail instead of blocking, it makes sense that `select` needs to return (otherwise the select would just hang forever if you didn't give a timeout). Reading the IO::Socket module, I was bit surprised that waiting for more than one condition type isn't easier. But anyway, I'd do this: `my $canWrite= IO::Select->new( $sock ); my $hasError= IO::Select->new( $sock ); my( $aWrite, $aError )= IO::Select->select( undef, $canWrite, $hasError ); for( @$aError ) { warn "Error on socket ($_).\n"; } for( @$aWrite ) { if( print $_ $message ) { print "message sent.\n"; } else { warn "Can't write to socket ($_): $!\n"; } }` [download] and see what happens. Then you have the error loop do recovery based on what behavior you see, etc.	[reply] [d/l] [select]