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# Copyrights and documentation are at the end.
package POE::Queue::Array;
use strict;
use vars qw($VERSION @ISA);
$VERSION = '1.293'; # NOTE - Should be #.### (three decimal places)
@ISA = qw(POE::Queue);
use Errno qw(ESRCH EPERM);
use Carp qw(confess);
sub DEBUG () { 0 }
### Helpful offsets.
sub ITEM_PRIORITY () { 0 }
sub ITEM_ID () { 1 }
sub ITEM_PAYLOAD () { 2 }
sub import {
my $package = caller();
no strict 'refs';
*{ $package . '::ITEM_PRIORITY' } = \&ITEM_PRIORITY;
*{ $package . '::ITEM_ID' } = \&ITEM_ID;
*{ $package . '::ITEM_PAYLOAD' } = \&ITEM_PAYLOAD;
}
# Item IDs are unique across all queues.
my $queue_seq = 0;
my %item_priority;
### A very simple constructor.
sub new {
bless [], shift();
}
### Add an item to the queue. Returns the new item's ID.
sub enqueue {
my ($self, $priority, $payload) = @_;
# Get the next item ID. This clever loop will hang indefinitely if
# you ever run out of integers to store things under. Map the ID to
# its due time for search-by-ID functions.
my $item_id;
1 while exists $item_priority{$item_id = ++$queue_seq};
$item_priority{$item_id} = $priority;
my $item_to_enqueue = [
$priority, # ITEM_PRIORITY
$item_id, # ITEM_ID
$payload, # ITEM_PAYLOAD
];
# Special case: No items in the queue. The queue IS the item.
unless (@$self) {
$self->[0] = $item_to_enqueue;
DEBUG and warn $self->_dump_splice(0);
return $item_id;
}
# Special case: The new item belongs at the end of the queue.
if ($priority >= $self->[-1]->[ITEM_PRIORITY]) {
push @$self, $item_to_enqueue;
DEBUG and warn $self->_dump_splice(@$self-1);
return $item_id;
}
# Special case: The new item belongs at the head of the queue.
if ($priority < $self->[0]->[ITEM_PRIORITY]) {
unshift @$self, $item_to_enqueue;
DEBUG and warn $self->_dump_splice(0);
return $item_id;
}
# Special case: There are only two items in the queue. This item
# naturally belongs between them.
if (@$self == 2) {
splice @$self, 1, 0, $item_to_enqueue;
DEBUG and warn $self->_dump_splice(1);
return $item_id;
}
# And finally we have a nontrivial queue. Insert the item using a
# binary seek.
$self->_insert_item(0, $#$self, $priority, $item_to_enqueue);
return $item_id;
}
### Dequeue the next thing from the queue. Returns an empty list if
### the queue is empty. There are different flavors of this
### operation.
sub dequeue_next {
my $self = shift;
return unless @$self;
my ($priority, $id, $stuff) = @{shift @$self};
delete $item_priority{$id};
return ($priority, $id, $stuff);
}
### Return the next item's priority, undef if the queue is empty.
# This is POE's most-called method. We could greatly benefit from
# finding ways to reduce the number of calls.
sub get_next_priority {
# This is Ton Hospel's optimization.
# He measured a 4% improvement by avoiding $self.
return (shift->[0] || return undef)->[ITEM_PRIORITY];
}
### Return the number of items currently in the queue.
sub get_item_count {
return scalar @{$_[0]};
}
### Internal method to insert an item using a binary seek and splice.
### We accept the bounds as parameters because the alarm adjustment
### functions may also use it.
sub _insert_item {
my ($self, $lower, $upper, $priority, $item) = @_;
while (1) {
my $midpoint = ($upper + $lower) >> 1;
# Upper and lower bounds crossed. Insert at the lower point.
if ($upper < $lower) {
splice @$self, $lower, 0, $item;
DEBUG and warn $self->_dump_splice($lower);
return;
}
# We're looking for a priority lower than the one at the midpoint.
# Set the new upper point to just before the midpoint.
if ($priority < $self->[$midpoint]->[ITEM_PRIORITY]) {
$upper = $midpoint - 1;
next;
}
# We're looking for a priority greater or equal to the one at the
# midpoint. The new lower bound is just after the midpoint.
$lower = $midpoint + 1;
}
}
### Internal method to find a queue item by its priority and ID. We
### assume the priority and ID have been verified already, so the item
### must exist. Returns the index of the item that matches the
### priority/ID pair.
sub _find_item {
my ($self, $id, $priority) = @_;
# Use a binary seek.
my $upper = $#$self; # Last index of @$self.
my $lower = 0;
while (1) {
my $midpoint = ($upper + $lower) >> 1;
# Upper and lower bounds crossed. The lower point is aimed at an
# element with a priority higher than our target.
last if $upper < $lower;
# We're looking for a priority lower than the one at the midpoint.
# Set the new upper point to just before the midpoint.
if ($priority < $self->[$midpoint]->[ITEM_PRIORITY]) {
$upper = $midpoint - 1;
next;
}
# We're looking for a priority greater or equal to the one at the
# midpoint. The new lower bound is just after the midpoint.
$lower = $midpoint + 1;
}
# The lower index is pointing to an element with a priority higher
# than our target. Scan backwards until we find the item with the
# target ID.
while ($lower-- >= 0) {
return $lower if $self->[$lower]->[ITEM_ID] == $id;
}
die "should never get here... maybe the queue is out of order";
}
### Remove an item by its ID. Takes a coderef filter, too, for
### examining the payload to be sure it really wants to leave. Sets
### $! and returns undef on failure.
sub remove_item {
my ($self, $id, $filter) = @_;
my $priority = $item_priority{$id};
unless (defined $priority) {
$! = ESRCH;
return;
}
# Find that darn item.
my $item_index = $self->_find_item($id, $priority);
# Test the item against the filter.
unless ($filter->($self->[$item_index]->[ITEM_PAYLOAD])) {
$! = EPERM;
return;
}
# Remove the item, and return it.
delete $item_priority{$id};
return @{splice @$self, $item_index, 1};
}
### Remove items matching a filter. Regrettably, this must scan the
### entire queue. An optional count limits the number of items to
### remove, and it may shorten execution times. Returns a list of
### references to priority/id/payload lists. This is intended to
### return all the items matching the filter, and the function's
### behavior is undefined when $count is less than the number of
### matching items.
sub remove_items {
my ($self, $filter, $count) = @_;
$count = @$self unless $count;
my @items;
my $i = @$self;
while ($i--) {
if ($filter->($self->[$i]->[ITEM_PAYLOAD])) {
my $removed_item = splice(@$self, $i, 1);
delete $item_priority{$removed_item->[ITEM_ID]};
unshift @items, $removed_item;
last unless --$count;
}
}
return @items;
}
### Adjust the priority of an item by a relative amount. Adds $delta
### to the priority of the $id'd object (if it matches $filter), and
### moves it in the queue.
sub adjust_priority {
my ($self, $id, $filter, $delta) = @_;
my $old_priority = $item_priority{$id};
unless (defined $old_priority) {
$! = ESRCH;
return;
}
# Find that darn item.
my $item_index = $self->_find_item($id, $old_priority);
# Test the item against the filter.
unless ($filter->($self->[$item_index]->[ITEM_PAYLOAD])) {
$! = EPERM;
return;
}
# Nothing to do if the delta is zero.
# TODO Actually we may need to ensure that the item is moved to the
# end of its current priority bucket, since it should have "moved".
return $self->[$item_index]->[ITEM_PRIORITY] unless $delta;
# Remove the item, and adjust its priority.
my $item = splice(@$self, $item_index, 1);
my $new_priority = $item->[ITEM_PRIORITY] += $delta;
$item_priority{$id} = $new_priority;
$self->_reinsert_item($new_priority, $delta, $item_index, $item);
}
### Set the priority to a specific amount. Replaces the item's
### priority with $new_priority (if it matches $filter), and moves it
### to the new location in the queue.
sub set_priority {
my ($self, $id, $filter, $new_priority) = @_;
my $old_priority = $item_priority{$id};
unless (defined $old_priority) {
$! = ESRCH;
return;
}
# Nothing to do if the old and new priorities match.
# TODO Actually we may need to ensure that the item is moved to the
# end of its current priority bucket, since it should have "moved".
return $new_priority if $new_priority == $old_priority;
# Find that darn item.
my $item_index = $self->_find_item($id, $old_priority);
# Test the item against the filter.
unless ($filter->($self->[$item_index]->[ITEM_PAYLOAD])) {
$! = EPERM;
return;
}
# Remove the item, and calculate the delta.
my $item = splice(@$self, $item_index, 1);
my $delta = $new_priority - $old_priority;
$item->[ITEM_PRIORITY] = $item_priority{$id} = $new_priority;
$self->_reinsert_item($new_priority, $delta, $item_index, $item);
}
### Sanity-check the results of an item insert. Verify that it
### belongs where it was put. Only called during debugging.
sub _dump_splice {
my ($self, $index) = @_;
my @return;
my $at = $self->[$index]->[ITEM_PRIORITY];
if ($index > 0) {
my $before = $self->[$index-1]->[ITEM_PRIORITY];
push @return, "before($before)";
confess "out of order: $before should be < $at" if $before > $at;
}
push @return, "at($at)";
if ($index < $#$self) {
my $after = $self->[$index+1]->[ITEM_PRIORITY];
push @return, "after($after)";
my @priorities = map {$_->[ITEM_PRIORITY]} @$self;
confess "out of order: $at should be < $after (@priorities)" if (
$at >= $after
);
}
return "@return";
}
### Reinsert an item into the queue. It has just been removed by
### adjust_priority() or set_priority() and needs to be replaced.
### This tries to be clever by not doing more work than necessary.
sub _reinsert_item {
my ($self, $new_priority, $delta, $item_index, $item) = @_;
# Now insert it back.
# The special cases are duplicates from enqueue(). We use the delta
# (direction) of the move and the old item index to narrow down the
# subsequent nontrivial insert if none of the special cases apply.
# Special case: No events in the queue. The queue IS the item.
unless (@$self) {
$self->[0] = $item;
DEBUG and warn $self->_dump_splice(0);
return $new_priority;
}
# Special case: The item belongs at the end of the queue.
if ($new_priority >= $self->[-1]->[ITEM_PRIORITY]) {
push @$self, $item;
DEBUG and warn $self->_dump_splice(@$self-1);
return $new_priority;
}
# Special case: The item belongs at the head of the queue.
if ($new_priority < $self->[0]->[ITEM_PRIORITY]) {
unshift @$self, $item;
DEBUG and warn $self->_dump_splice(0);
return $new_priority;
}
# Special case: There are only two items in the queue. This item
# naturally belongs between them.
if (@$self == 2) {
splice @$self, 1, 0, $item;
DEBUG and warn $self->_dump_splice(1);
return $new_priority;
}
# The item has moved towards an end of the queue, but there are a
# lot of items into which it may be inserted. We'll binary seek.
my ($upper, $lower);
if ($delta > 0) {
$upper = $#$self; # Last index in @$self.
$lower = $item_index;
}
else {
$upper = $item_index;
$lower = 0;
}
$self->_insert_item($lower, $upper, $new_priority, $item);
return $new_priority;
}
### Peek at items that match a filter. Returns a list of payloads
### that match the supplied coderef.
sub peek_items {
my ($self, $filter, $count) = @_;
$count = @$self unless $count;
my @items;
my $i = @$self;
while ($i--) {
if ($filter->($self->[$i]->[ITEM_PAYLOAD])) {
unshift @items, $self->[$i];
last unless --$count;
}
}
return @items;
}
1;
__END__
=head1 NAME
POE::Queue::Array - a high-performance array-based priority queue
=head1 SYNOPSIS
See L<POE::Queue>.
=head1 DESCRIPTION
This class is an implementation of the abstract POE::Queue interface.
As such, its documentation may be found in L<POE::Queue>.
POE::Queue::Array implements a priority queue using Perl arrays,
splice, and copious application of cleverness.
Despite its name, POE::Queue::Array may be used as a stand-alone
priority queue without the rest of POE.
=head1 SEE ALSO
L<POE>, L<POE::Queue>
=head1 BUGS
None known.
=head1 AUTHORS & COPYRIGHTS
Please see L<POE> for more information about authors, contributors,
and POE's licensing.
=cut
# rocco // vim: ts=2 sw=2 expandtab
# TODO - Edit.
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