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IO::Select(3)          Perl Programmers Reference Guide          IO::Select(3)

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

           use IO::Select;

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


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

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

       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.

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

       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.

           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.

           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.

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

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

                       # Maybe we have finished with the socket

       Graham Barr. Currently maintained by the Perl Porters.  Please report all bugs to <>.

       Copyright (c) 1997-8 Graham Barr <>. All rights reserved.  This program is free software; you
       can redistribute it and/or modify it under the same terms as Perl itself.

perl v5.8.8                       2001-09-21                     IO::Select(3)