Lars Stoltenow > List-PriorityQueue > List::PriorityQueue

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NAME ^

List::PriorityQueue - high performance priority list (pure perl)

SYNOPSIS ^

 my $prio = new List::PriorityQueue;
 $prio->insert("foo", 2);
 $prio->insert("bar", 1);
 $prio->insert("baz", 3);
 my $next = $prio->pop(); # "bar"
 # I decided that "foo" isn't as important anymore
 $prio->update("foo", 99);

DESCRIPTION ^

This module implements a high-performance priority list. It's written in pure Perl.

Available functions are:

new()

Obvious.

insert($payload, $priority)

update($payload, $new_priority)

Adds the specified payload (anything fitting into a scalar) to the priority queue, using the specified priority. Smaller means more important.

If the item already exists in the queue, it is assigned the new priority. It's optimized to perform better than a delete followed by insert.

These names are actually the same function. The alternative name is provided so you can make clear which operation you intended to be executed.

pop()

Removes the most important item (numerically lowest priority) from the queue and returns it. If no element is there, returns undef.

delete($payload)

Deletes an item known by the specified payload from the queue.

unchecked_insert($payload, $priority)

unchecked_update($payload, $new_priority)

These functions are provided as an alternative to the safe (or "checked") functions described above. By bypassing some checks, they gain you a speed advantage, but if you don't know what you're doing, using these might corrupt/confuse the queue.

You can use these if you definitely know that the element doesn't exist yet for unchecked_insert, or that the element definitely already exists for unchecked_update.

DIFFERENCES TO POE::QUEUE::ARRAY ^

There are some things I disliked about POE::Queue::Array, which ultimately led to the creation of this derivative.

First, it stores data in a package global variable. The author brings up a valid argument why this is not bad in this case. However I still was somehow not happy with the fact it used a global variable. For example, serializing a queue would not work as the actual queue reference only stores numerical IDs into the package variable containing all the data, but that one wouldn't be saved.

Second, for some operations to be carried out efficiently, you have to carry the internal IDs around in your program, else you have to do a full search for your element everytime you want to delete or update it. While carrying it around is relatively simple, there is no reason why the class itself shouldn't manage this and relieve the programmer from this work.

A benchmark with POE::Queue::Array and the described payload-to-ID mapping and this module revealed that they are equally fast.

BUGS ^

Maybe.

SEE ALSO ^

POE::Queue::Array

AUTHORS & COPYRIGHTS ^

Made 2009 by Lars Stoltenow. List::PriorityQueue is free software; you may redistribute it and/or modify it under the same terms as Perl itself.

POE::Queue::Array is Copyright 1998-2007 Rocco Caputo. All rights reserved. Same license.

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