Select.pm

# IO::Select.pm
#
# 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.

package IO::Select;

use     strict;
use warnings::register;
require Exporter;

our $VERSION = "1.47";

our @ISA = qw(Exporter); # This is only so we can do version checking

sub VEC_BITS () {0}
sub FD_COUNT () {1}
sub FIRST_FD () {2}

sub new
{
 my $self = shift;
 my $type = ref($self) || $self;

 my $vec = bless [undef,0], $type;

 $vec->add(@_)
    if @_;

 $vec;
}

sub add
{
 shift->_update('add', @_);
}


sub remove
{
 shift->_update('remove', @_);
}


sub exists
{
 my $vec = shift;
 my $fno = $vec->_fileno(shift);
 return undef unless defined $fno;
 $vec->[$fno + FIRST_FD];
}


sub _fileno
{
 my($self, $f) = @_;
 return unless defined $f;
 $f = $f->[0] if ref($f) eq 'ARRAY';
 if($f =~ /^[0-9]+$/) { # plain file number
  return $f;
 }
 elsif(defined(my $fd = fileno($f))) {
  return $fd;
 }
 else {
  # Neither a plain file number nor an opened filehandle; but maybe it was
  # previously registered and has since been closed. ->remove still wants to
  # know what fileno it had
  foreach my $i ( FIRST_FD .. $#$self ) {
   return $i - FIRST_FD if $self->[$i] == $f;
  }
  return undef;
 }
}

sub _update
{
 my $vec = shift;
 my $add = shift eq 'add';

 my $bits = $vec->[VEC_BITS];
 $bits = '' unless defined $bits;

 my $count = 0;
 my $f;
 foreach $f (@_)
  {
   my $fn = $vec->_fileno($f);
   if ($add) {
     next unless defined $fn;
     my $i = $fn + FIRST_FD;
     if (defined $vec->[$i]) {
	 $vec->[$i] = $f;  # if array rest might be different, so we update
	 next;
     }
     $vec->[FD_COUNT]++;
     vec($bits, $fn, 1) = 1;
     $vec->[$i] = $f;
   } else {      # remove
     if ( ! defined $fn ) { # remove if fileno undef'd
       $fn = 0;
       for my $fe (@{$vec}[FIRST_FD .. $#$vec]) {
         if (defined($fe) && $fe == $f) {
	   $vec->[FD_COUNT]--;
	   $fe = undef;
	   vec($bits, $fn, 1) = 0;
	   last;
	 }
	 ++$fn;
       }
     }
     else {
       my $i = $fn + FIRST_FD;
       next unless defined $vec->[$i];
       $vec->[FD_COUNT]--;
       vec($bits, $fn, 1) = 0;
       $vec->[$i] = undef;
     }
   }
   $count++;
  }
 $vec->[VEC_BITS] = $vec->[FD_COUNT] ? $bits : undef;
 $count;
}

sub can_read
{
 my $vec = shift;
 my $timeout = shift;
 my $r = $vec->[VEC_BITS];

 defined($r) && (select($r,undef,undef,$timeout) > 0)
    ? handles($vec, $r)
    : ();
}

sub can_write
{
 my $vec = shift;
 my $timeout = shift;
 my $w = $vec->[VEC_BITS];

 defined($w) && (select(undef,$w,undef,$timeout) > 0)
    ? handles($vec, $w)
    : ();
}

sub has_exception
{
 my $vec = shift;
 my $timeout = shift;
 my $e = $vec->[VEC_BITS];

 defined($e) && (select(undef,undef,$e,$timeout) > 0)
    ? handles($vec, $e)
    : ();
}

sub has_error
{
 warnings::warn("Call to deprecated method 'has_error', use 'has_exception'")
	if warnings::enabled();
 goto &has_exception;
}

sub count
{
 my $vec = shift;
 $vec->[FD_COUNT];
}

sub bits
{
 my $vec = shift;
 $vec->[VEC_BITS];
}

sub as_string  # for debugging
{
 my $vec = shift;
 my $str = ref($vec) . ": ";
 my $bits = $vec->bits;
 my $count = $vec->count;
 $str .= defined($bits) ? unpack("b*", $bits) : "undef";
 $str .= " $count";
 my @handles = @$vec;
 splice(@handles, 0, FIRST_FD);
 for (@handles) {
     $str .= " " . (defined($_) ? "$_" : "-");
 }
 $str;
}

sub _max
{
 my($a,$b,$c) = @_;
 $a > $b
    ? $a > $c
        ? $a
        : $c
    : $b > $c
        ? $b
        : $c;
}

sub select
{
 shift
   if defined $_[0] && !ref($_[0]);

 my($r,$w,$e,$t) = @_;
 my @result = ();

 my $rb = defined $r ? $r->[VEC_BITS] : undef;
 my $wb = defined $w ? $w->[VEC_BITS] : undef;
 my $eb = defined $e ? $e->[VEC_BITS] : undef;

 if(select($rb,$wb,$eb,$t) > 0)
  {
   my @r = ();
   my @w = ();
   my @e = ();
   my $i = _max(defined $r ? scalar(@$r)-1 : 0,
                defined $w ? scalar(@$w)-1 : 0,
                defined $e ? scalar(@$e)-1 : 0);

   for( ; $i >= FIRST_FD ; $i--)
    {
     my $j = $i - FIRST_FD;
     push(@r, $r->[$i])
        if defined $rb && defined $r->[$i] && vec($rb, $j, 1);
     push(@w, $w->[$i])
        if defined $wb && defined $w->[$i] && vec($wb, $j, 1);
     push(@e, $e->[$i])
        if defined $eb && defined $e->[$i] && vec($eb, $j, 1);
    }

   @result = (\@r, \@w, \@e);
  }
 @result;
}


sub handles
{
 my $vec = shift;
 my $bits = shift;
 my @h = ();
 my $i;
 my $max = scalar(@$vec) - 1;

 for ($i = FIRST_FD; $i <= $max; $i++)
  {
   next unless defined $vec->[$i];
   push(@h, $vec->[$i])
      if !defined($bits) || vec($bits, $i - FIRST_FD, 1);
  }
 
 @h;
}

1;
__END__

=head1 NAME

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

=head1 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);

=head1 DESCRIPTION

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

=head1 CONSTRUCTOR

=over 4

=item new ( [ HANDLES ] )

The constructor creates a new object and optionally initialises it with a set
of handles.

=back

=head1 METHODS

=over 4

=item add ( HANDLES )

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

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

=item remove ( HANDLES )

Remove all the given handles from the object. This method also works
by the C<fileno> of the handles. So the exact handles that were added
need not be passed, just handles that have an equivalent C<fileno>

=item exists ( HANDLE )

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

=item handles

Return an array of all registered handles.

=item can_read ( [ TIMEOUT ] )

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

=item can_write ( [ TIMEOUT ] )

Same as C<can_read> except check for handles that can be written to.

=item has_exception ( [ TIMEOUT ] )

Same as C<can_read> except check for handles that have an exception
condition, for example pending out-of-band data.

=item count ()

Returns the number of handles that the object will check for when
one of the C<can_> methods is called or the object is passed to
the C<select> static method.

=item bits()

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

=item select ( READ, WRITE, EXCEPTION [, TIMEOUT ] )

C<select> is a static method, that is you call it with the package name
like C<new>. C<READ>, C<WRITE> and C<EXCEPTION> are either C<undef> or
C<IO::Select> objects. C<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 C<$!> unchanged.  Upon error, an empty list is returned, with C<$!>
set to indicate the error.  To distinguish between timeout and error,
set C<$!> to zero before calling this method, and check it after an
empty list is returned.

=back

=head1 EXAMPLE

Here is a short example which shows how C<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;
            }
        }
    }

=head1 AUTHOR

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

=head1 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.

=cut