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.\"
.IX Title "IO::Select 3"
.TH IO::Select 3 "2002-11-24" "perl v5.8.0" "Perl Programmers Reference Guide"
.SH "NAME"
IO::Select \- OO interface to the select system call
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&    use IO::Select;
.Ve
.PP
.Vb 1
\&    $s = IO::Select->new();
.Ve
.PP
.Vb 2
\&    $s->add(\e*STDIN);
\&    $s->add($some_handle);
.Ve
.PP
.Vb 1
\&    @ready = $s->can_read($timeout);
.Ve
.PP
.Vb 1
\&    @ready = IO::Select->new(@handles)->read(0);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \f(CW\*(C`IO::Select\*(C'\fR package implements an object approach to the system \f(CW\*(C`select\*(C'\fR
function call. It allows the user to see what \s-1IO\s0 handles, see IO::Handle,
are ready for reading, writing or have an error condition pending.
.SH "CONSTRUCTOR"
.IX Header "CONSTRUCTOR"
.IP "new ( [ \s-1HANDLES\s0 ] )" 4
.IX Item "new ( [ HANDLES ] )"
The constructor creates a new object and optionally initialises it with a set
of handles.
.SH "METHODS"
.IX Header "METHODS"
.IP "add ( \s-1HANDLES\s0 )" 4
.IX Item "add ( HANDLES )"
Add the list of handles to the \f(CW\*(C`IO::Select\*(C'\fR object. It is these values that
will be returned when an event occurs. \f(CW\*(C`IO::Select\*(C'\fR keeps these values in a
cache which is indexed by the \f(CW\*(C`fileno\*(C'\fR of the handle, so if more than one
handle with the same \f(CW\*(C`fileno\*(C'\fR is specified then only the last one is cached.
.Sp
Each handle can be an \f(CW\*(C`IO::Handle\*(C'\fR object, an integer or an array
reference where the first element is an \f(CW\*(C`IO::Handle\*(C'\fR or an integer.
.IP "remove ( \s-1HANDLES\s0 )" 4
.IX Item "remove ( HANDLES )"
Remove all the given handles from the object. This method also works
by the \f(CW\*(C`fileno\*(C'\fR of the handles. So the exact handles that were added
need not be passed, just handles that have an equivalent \f(CW\*(C`fileno\*(C'\fR
.IP "exists ( \s-1HANDLE\s0 )" 4
.IX Item "exists ( HANDLE )"
Returns a true value (actually the handle itself) if it is present.
Returns undef otherwise.
.IP "handles" 4
.IX Item "handles"
Return an array of all registered handles.
.IP "can_read ( [ \s-1TIMEOUT\s0 ] )" 4
.IX Item "can_read ( [ TIMEOUT ] )"
Return an array of handles that are ready for reading. \f(CW\*(C`TIMEOUT\*(C'\fR is
the maximum amount of time to wait before returning an empty list, in
seconds, possibly fractional. If \f(CW\*(C`TIMEOUT\*(C'\fR is not given and any
handles are registered then the call will block.
.IP "can_write ( [ \s-1TIMEOUT\s0 ] )" 4
.IX Item "can_write ( [ TIMEOUT ] )"
Same as \f(CW\*(C`can_read\*(C'\fR except check for handles that can be written to.
.IP "has_exception ( [ \s-1TIMEOUT\s0 ] )" 4
.IX Item "has_exception ( [ TIMEOUT ] )"
Same as \f(CW\*(C`can_read\*(C'\fR except check for handles that have an exception
condition, for example pending out-of-band data.
.IP "count ()" 4
.IX Item "count ()"
Returns the number of handles that the object will check for when
one of the \f(CW\*(C`can_\*(C'\fR methods is called or the object is passed to
the \f(CW\*(C`select\*(C'\fR static method.
.IP "\fIbits()\fR" 4
.IX Item "bits()"
Return the bit string suitable as argument to the core \fIselect()\fR call.
.IP "select ( \s-1READ\s0, \s-1WRITE\s0, \s-1ERROR\s0 [, \s-1TIMEOUT\s0 ] )" 4
.IX Item "select ( READ, WRITE, ERROR [, TIMEOUT ] )"
\&\f(CW\*(C`select\*(C'\fR is a static method, that is you call it with the package
name like \f(CW\*(C`new\*(C'\fR. \f(CW\*(C`READ\*(C'\fR, \f(CW\*(C`WRITE\*(C'\fR and \f(CW\*(C`ERROR\*(C'\fR are either \f(CW\*(C`undef\*(C'\fR
or \f(CW\*(C`IO::Select\*(C'\fR objects. \f(CW\*(C`TIMEOUT\*(C'\fR is optional and has the same
effect as for the core select call.
.Sp
The result will be an array of 3 elements, each a reference to an array
which will hold the handles that are ready for reading, writing and have
error conditions respectively. Upon error an empty array is returned.
.SH "EXAMPLE"
.IX Header "EXAMPLE"
Here is a short example which shows how \f(CW\*(C`IO::Select\*(C'\fR could be used
to write a server which communicates with several sockets while also
listening for more connections on a listen socket
.PP
.Vb 2
\&    use IO::Select;
\&    use IO::Socket;
.Ve
.PP
.Vb 2
\&    $lsn = new IO::Socket::INET(Listen => 1, LocalPort => 8080);
\&    $sel = new IO::Select( $lsn );
.Ve
.PP
.Vb 9
\&    while(@ready = $sel->can_read) {
\&        foreach $fh (@ready) {
\&            if($fh == $lsn) {
\&                # Create a new socket
\&                $new = $lsn->accept;
\&                $sel->add($new);
\&            }
\&            else {
\&                # Process socket
.Ve
.PP
.Vb 6
\&                # Maybe we have finished with the socket
\&                $sel->remove($fh);
\&                $fh->close;
\&            }
\&        }
\&    }
.Ve
.SH "AUTHOR"
.IX Header "AUTHOR"
Graham Barr. Currently maintained by the Perl Porters.  Please report all
bugs to <perl5\-porters@perl.org>.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright (c) 1997\-8 Graham Barr <gbarr@pobox.com>. All rights reserved.
This program is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.