phpman > perldoc > IO::Select(3perl)

NAME
    IO::Select - OO interface to the select system call

SYNOPSIS
        use IO::Select;

        $s = IO::Select->new();

        $s->add(\*STDIN);
        $s->add($some_handle);

        @ready = $s->can_read($timeout);

        @ready = IO::Select->new(@handles)->can_read(0);

DESCRIPTION
    The "IO::Select" package implements an object approach to the system "select" function call. It
    allows the user to see what IO handles, see IO::Handle, are ready for reading, writing or have
    an exception pending.

CONSTRUCTOR
    new ( [ HANDLES ] )
        The constructor creates a new object and optionally initialises it with a set of handles.

METHODS
    add ( HANDLES )
        Add the list of handles to the "IO::Select" object. It is these values that will be returned
        when an event occurs. "IO::Select" keeps these values in a cache which is indexed by the
        "fileno" of the handle, so if more than one handle with the same "fileno" is specified then
        only the last one is cached.

        Each handle can be an "IO::Handle" object, an integer or an array reference where the first
        element is an "IO::Handle" or an integer.

    remove ( HANDLES )
        Remove all the given handles from the object. This method also works by the "fileno" of the
        handles. So the exact handles that were added need not be passed, just handles that have an
        equivalent "fileno"

    exists ( HANDLE )
        Returns a true value (actually the handle itself) if it is present. Returns undef otherwise.

    handles
        Return an array of all registered handles.

    can_read ( [ TIMEOUT ] )
        Return an array of handles that are ready for reading. "TIMEOUT" is the maximum amount of
        time to wait before returning an empty list (with $! unchanged), in seconds, possibly
        fractional. If "TIMEOUT" is not given and any handles are registered then the call will
        block indefinitely. Upon error, an empty list is returned, with $! set to indicate the
        error. To distinguish between timeout and error, set $! to zero before calling this method,
        and check it after an empty list is returned.

    can_write ( [ TIMEOUT ] )
        Same as "can_read" except check for handles that can be written to.

    has_exception ( [ TIMEOUT ] )
        Same as "can_read" except check for handles that have an exception condition, for example
        pending out-of-band data.

    count ()
        Returns the number of handles that the object will check for when one of the "can_" methods
        is called or the object is passed to the "select" static method.

    bits()
        Return the bit string suitable as argument to the core select() call.

    select ( READ, WRITE, EXCEPTION [, TIMEOUT ] )
        "select" is a static method, that is you call it with the package name like "new". "READ",
        "WRITE" and "EXCEPTION" are either "undef" or "IO::Select" objects. "TIMEOUT" is optional
        and has the same effect as for the core select call.

        If at least one handle is ready for the specified kind of operation, 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 exceptions respectively. Upon timeout, an empty list is
        returned, with $! unchanged. Upon error, an empty list is returned, with $! set to indicate
        the error. To distinguish between timeout and error, set $! to zero before calling this
        method, and check it after an empty list is returned.

EXAMPLE
    Here is a short example which shows how "IO::Select" could be used to write a server which
    communicates with several sockets while also listening for more connections on a listen socket

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

        $lsn = IO::Socket::INET->new(Listen => 1, LocalPort => 8080);
        $sel = IO::Select->new( $lsn );

        while(@ready = $sel->can_read) {
            foreach $fh (@ready) {
                if($fh == $lsn) {
                    # Create a new socket
                    $new = $lsn->accept;
                    $sel->add($new);
                }
                else {
                    # Process socket

                    # Maybe we have finished with the socket
                    $sel->remove($fh);
                    $fh->close;
                }
            }
        }

AUTHOR
    Graham Barr. Currently maintained by the Perl Porters. Please report all bugs to
    <perlbug AT perl.org>.

COPYRIGHT
    Copyright (c) 1997-8 Graham Barr <gbarr AT 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.