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# IO::Select

Perl 5 version 26.0 documentation
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# IO::Select

- NAME
- SYNOPSIS
- DESCRIPTION
- CONSTRUCTOR
- METHODS
- EXAMPLE
- AUTHOR
- COPYRIGHT

# 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, in seconds, possibly fractional. If `TIMEOUT` is not given and any handles are registered then the call will block.

- 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.

  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 error 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@perl.org>.

# 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.

Page index

- NAME
- SYNOPSIS
- DESCRIPTION
- CONSTRUCTOR
- METHODS
- EXAMPLE
- AUTHOR
- COPYRIGHT