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Thread::Queue(3pm)     Perl Programmers Reference Guide     Thread::Queue(3pm)

NAME
       Thread::Queue - Thread-safe queues

VERSION
       This document describes Thread::Queue version 2.11

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>

       Annotated POD for Thread::Queue:
       http://annocpan.org/~JDHEDDEN/Thread-Queue-2.11/lib/Thread/Queue.pm
       <http://annocpan.org/~JDHEDDEN/Thread-Queue-2.11/lib/Thread/Queue.pm>

       Source repository: http://code.google.com/p/thread-queue/
       <http://code.google.com/p/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 v5.12.1                      2010-04-26                Thread::Queue(3pm)
 

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Gedruckt am: 20.09.2017 03:54 GMT+0200 (2017-09-20T03:54:26+02:00)