file::queue(3pm) [debian man page]
File::Queue(3pm) User Contributed Perl Documentation File::Queue(3pm) NAME
File::Queue - Persistent FIFO queue implemented in pure perl! SYNOPSIS
use strict; # always! use File::Queue; my $q = new File::Queue (File => '/var/spool/yourprog/queue'); $q->enq('some flat text1'); $q->enq('some flat text2'); $q->enq('some flat text3'); # Get up to first 10 elements my $contents = $q->peek(10); my $elem1 = $q->deq(); my $elem2 = $q->deq(); # empty the queue $q->reset(); DESCRIPTION
This module allows for the creation of persistent FIFO queue objects. File::Queue only handles scalars as queue elements. If you want to work with references, serialize them first! The module was written with speed in mind, and it is very fast, but it should be used with care. Please refer to the CAVEATS section. Interface File::Queue implements a OO interface. The object methods and parameters are described below. Methods File::Queue supports all of the queue-related functions a developer should expect. o new() Instantiates your File::Queue object. Parameters are described in the next sub-section. o enq() Enqueues a string element to the queue. o deq() Dequeues a string element from the queue, and returns the element. If the queue is empty, nothing is returned. o peek(n) Returns an arrayref containing the next n elements in the queue. If the queue size is less than n, all elements are returned. If the queue is empty, an empty arrayref is returned. o reset() Emptys the queue. o close() Closes the filehandles belonging to the queue object ('.dat' and '.idx'). o delete() Deletes the files belonging to the queue object ('.dat' and '.idx'). Parameters There are a number of parameters that can be passed when constructing your File::Queue objects. Parameters are case-insensitive. o File (required) File::Queue creates two files using this parameter as the base. In the case of the example in the SYNOPSIS, the two files are '/var/spool/yourprog/queue.dat' and '/var/spool/yourprog.idx'. The '.dat' file holds all of the data, the '.idx' file holds the byte index (pointer) of the starting point of the first element in the queue. o Mode (optional) The file bit mode to be shared by both the '.dat' and '.idx' files. Defaults to '0600'. o Seperator (optional) The character or byte sequence that is used to seperate queue elements in the '.dat' file. It should be something you can guarantee will NEVER appear in your queue data. Defaults to the newline character. o BlockSize (optional) This is the size of the byte chunks that are pulled at each iteration when checking for the end of a queued element. Defaults to 64, which will be fine for most cases, but can be tweaked or tuned for your specific case to squeeze out a few extra nanoseconds. CAVEATS
This module should never be used in situations where the queue is not expected to become empty. The '.dat' file is not truncated (emptied) until the queue is empty. Even the data you've already dequeued remains in the '.dat' file until the queue is empty. If you keep enqueueing elements and never FULLY dequeue everything, eventually your disk will fill up! SEE ALSO
Tie::File AUTHOR
Jason Lavold <jlavold [ at ] gmail.com> perl v5.10.0 2008-12-22 File::Queue(3pm)
Check Out this Related Man Page
Thread::Queue(3perl) Perl Programmers Reference Guide Thread::Queue(3perl) NAME
Thread::Queue - Thread-safe queues VERSION
This document describes Thread::Queue version 2.12 SYNOPSIS
use strict; use warnings; use threads; use Thread::Queue; my $q = Thread::Queue->new(); # A new empty queue # Worker thread my $thr = threads->create(sub { while (my $item = $q->dequeue()) { # Do work on $item } })->detach(); # Send work to the thread $q->enqueue($item1, ...); # Count of items in the queue my $left = $q->pending(); # Non-blocking dequeue if (defined(my $item = $q->dequeue_nb())) { # Work on $item } # Get the second item in the queue without dequeuing anything my $item = $q->peek(1); # Insert two items into the queue just behind the head $q->insert(1, $item1, $item2); # Extract the last two items on the queue my ($item1, $item2) = $q->extract(-2, 2); DESCRIPTION
This module provides thread-safe FIFO queues that can be accessed safely by any number of threads. Any data types supported by threads::shared can be passed via queues: Ordinary scalars Array refs Hash refs Scalar refs Objects based on the above Ordinary scalars are added to queues as they are. If not already thread-shared, the other complex data types will be cloned (recursively, if needed, and including any "bless"ings and read- only settings) into thread-shared structures before being placed onto a queue. For example, the following would cause Thread::Queue to create a empty, shared array reference via "&shared([])", copy the elements 'foo', 'bar' and 'baz' from @ary into it, and then place that shared reference onto the queue: my @ary = qw/foo bar baz/; $q->enqueue(@ary); However, for the following, the items are already shared, so their references are added directly to the queue, and no cloning takes place: my @ary :shared = qw/foo bar baz/; $q->enqueue(@ary); my $obj = &shared({}); $$obj{'foo'} = 'bar'; $$obj{'qux'} = 99; bless($obj, 'My::Class'); $q->enqueue($obj); See "LIMITATIONS" for caveats related to passing objects via queues. QUEUE CREATION
->new() Creates a new empty queue. ->new(LIST) Creates a new queue pre-populated with the provided list of items. BASIC METHODS
The following methods deal with queues on a FIFO basis. ->enqueue(LIST) Adds a list of items onto the end of the queue. ->dequeue() ->dequeue(COUNT) Removes the requested number of items (default is 1) from the head of the queue, and returns them. If the queue contains fewer than the requested number of items, then the thread will be blocked until the requisite number of items are available (i.e., until other threads <enqueue> more items). ->dequeue_nb() ->dequeue_nb(COUNT) Removes the requested number of items (default is 1) from the head of the queue, and returns them. If the queue contains fewer than the requested number of items, then it immediately (i.e., non-blocking) returns whatever items there are on the queue. If the queue is empty, then "undef" is returned. ->pending() Returns the number of items still in the queue. ADVANCED METHODS
The following methods can be used to manipulate items anywhere in a queue. To prevent the contents of a queue from being modified by another thread while it is being examined and/or changed, lock the queue inside a local block: { lock($q); # Keep other threads from changing the queue's contents my $item = $q->peek(); if ($item ...) { ... } } # Queue is now unlocked ->peek() ->peek(INDEX) Returns an item from the queue without dequeuing anything. Defaults to the the head of queue (at index position 0) if no index is specified. Negative index values are supported as with arrays (i.e., -1 is the end of the queue, -2 is next to last, and so on). If no items exists at the specified index (i.e., the queue is empty, or the index is beyond the number of items on the queue), then "undef" is returned. Remember, the returned item is not removed from the queue, so manipulating a "peek"ed at reference affects the item on the queue. ->insert(INDEX, LIST) Adds the list of items to the queue at the specified index position (0 is the head of the list). Any existing items at and beyond that position are pushed back past the newly added items: $q->enqueue(1, 2, 3, 4); $q->insert(1, qw/foo bar/); # Queue now contains: 1, foo, bar, 2, 3, 4 Specifying an index position greater than the number of items in the queue just adds the list to the end. Negative index positions are supported: $q->enqueue(1, 2, 3, 4); $q->insert(-2, qw/foo bar/); # Queue now contains: 1, 2, foo, bar, 3, 4 Specifying a negative index position greater than the number of items in the queue adds the list to the head of the queue. ->extract() ->extract(INDEX) ->extract(INDEX, COUNT) Removes and returns the specified number of items (defaults to 1) from the specified index position in the queue (0 is the head of the queue). When called with no arguments, "extract" operates the same as "dequeue_nb". This method is non-blocking, and will return only as many items as are available to fulfill the request: $q->enqueue(1, 2, 3, 4); my $item = $q->extract(2) # Returns 3 # Queue now contains: 1, 2, 4 my @items = $q->extract(1, 3) # Returns (2, 4) # Queue now contains: 1 Specifying an index position greater than the number of items in the queue results in "undef" or an empty list being returned. $q->enqueue('foo'); my $nada = $q->extract(3) # Returns undef my @nada = $q->extract(1, 3) # Returns () Negative index positions are supported. Specifying a negative index position greater than the number of items in the queue may return items from the head of the queue (similar to "dequeue_nb") if the count overlaps the head of the queue from the specified position (i.e. if queue size + index + count is greater than zero): $q->enqueue(qw/foo bar baz/); my @nada = $q->extract(-6, 2); # Returns () - (3+(-6)+2) <= 0 my @some = $q->extract(-6, 4); # Returns (foo) - (3+(-6)+4) > 0 # Queue now contains: bar, baz my @rest = $q->extract(-3, 4); # Returns (bar, baz) - (2+(-3)+4) > 0 NOTES
Queues created by Thread::Queue can be used in both threaded and non-threaded applications. LIMITATIONS
Passing objects on queues may not work if the objects' classes do not support sharing. See "BUGS AND LIMITATIONS" in threads::shared for more. Passing array/hash refs that contain objects may not work for Perl prior to 5.10.0. SEE ALSO
Thread::Queue Discussion Forum on CPAN: http://www.cpanforum.com/dist/Thread-Queue <http://www.cpanforum.com/dist/Thread-Queue> threads, threads::shared MAINTAINER
Jerry D. Hedden, <jdhedden AT cpan DOT org> LICENSE
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. perl v5.14.2 2011-09-19 Thread::Queue(3perl)