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   at
       <https://github.com/Perl/perl5/issues>.

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.

perl v5.38.2                                       2025-04-08                                  IO::Select(3perl)