http://qs321.pair.com?node_id=485475


in reply to Re: New to perl: IO Select question :(
in thread New to perl: IO Select question :(

I don't think you're right on this one. His code works fine as long as you just replace

my @rhSet = IO::Select->select($readSet, undef, undef, 0);
foreach my $rh (@{$rhSet[0]}) {

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with (as in your example)
my @rhSet = IO::Select->select($readSet, undef, undef, 0);
foreach my $rh (@{$rhSet[0]}) {

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The

my $connection = $sock->accept();
$readSet->add($connection);

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you added are not needed, and I'd personally consider doing that more harmful than useful.

I also don't understand your comment about $sock not being an "active channel". After you create a server socket you can add it to the read set perfectly fine, and the select will return the socket when there's a connection to accept.

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Re^3: New to perl: IO Select question :(
by pg (Canon) on Aug 21, 2005 at 03:50 UTC

    For server side, one cares whether each connection can read or write, not the listening server socket. The listening socket does not read or write.

    Let's do a simple testing. With the following client and server:

    #server
use strict;
use warnings;

use IO::Socket;
use IO::Select;

my $sock = IO::Socket::INET->new(Proto=>"tcp", LocalHost=>"localhost",
+ 
Listen=>16, Reuse=>1, LocalPort=>3000) 
    || die("Could not create socket!\n");
my $conn = $sock->accept();
my $sel = new IO::Select($sock);
if ($sel->can_read()) {
    print "can read\n";
}
#client
use IO::Socket;

my $sock = IO::Socket::INET->new(
                                Proto=>"tcp",
                                PeerHost=>"Localhost",
                                PeerPort=>3000
                                ) or die("Could not create socket!\n")
+;


print $sock "abcd\n";

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    Run perl -w server.pl in one window, then run perl -w client.pl in another window, nothing gets printed in the server window! run perl -w client.pl again, "abcd" gets printed. This is not what one will want.

    change server code:

    use strict;
use warnings;

use IO::Socket;
use IO::Select;

my $sock = IO::Socket::INET->new(Proto=>"tcp", LocalHost=>"localhost",
+ 
Listen=>16, Reuse=>1, LocalPort=>3000) 
    || die("Could not create socket!\n");
my $conn = $sock->accept();
my $sel = new IO::Select($conn);
if ($sel->can_read()) {
    print "can read\n";
}

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    The first time you run perl -w client.pl, server side knows that it can read, and prints "abcd". That's what one wants.

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      For server side, one cares whether each connection can read or write, not the listening server socket. The listening socket does not read or write.

      This is false, and your example is not analogous to the original post. A listening socket becomes readable when a connection is ready to be accept()ed. His code correctly tests the listening socket and all open client connections, reacting to a readable state on the listening socket with an accept(), and on all other sockets with a read. (The read isn't quite right since it blocks waiting for a full line, but the intent is fairly clear.)

      Your version blocks on an extraneous accept() before hitting the select(), and is unable to ever accept any more connections. Your "simple testing" fails because it doesn't select on the listening socket until after it pulls the first connection off of it. So, yes, that select() doesn't fall through until a second connection comes in. His code doesn't have that flaw.

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[d/l]
[select]

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