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

NAME
       Thread::Queue - Thread-safe queues

VERSION
       This document describes Thread::Queue version 3.12

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 {
		   # Thread will loop until no more work
		   while (defined(my $item = $q->dequeue())) {
		       # Do work on $item
		       ...
		   }
	       }
	   );

	   # Send work to the thread
	   $q->enqueue($item1, ...);
	   # Signal that there is no more work to be sent
	   $q->end();
	   # Join up with the thread when it finishes
	   $thr->join();

	   ...

	   # Count of items in the queue
	   my $left = $q->pending();

	   # Non-blocking dequeue
	   if (defined(my $item	= $q->dequeue_nb())) {
	       # Work on $item
	   }

	   # Blocking dequeue with 5-second timeout
	   if (defined(my $item	= $q->dequeue_timed(5))) {
	       # Work on $item
	   }

	   # Set a size	for a queue
	   $q->limit = 5;

	   # 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.

       ->dequeue_timed(TIMEOUT)
       ->dequeue_timed(TIMEOUT,	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, or until the
	   timeout is reached.	If the timeout is reached, it returns whatever
	   items there are on the queue, or "undef" if the queue is empty.

	   The timeout may be a	number of seconds relative to the current time
	   (e.g., 5 seconds from when the call is made), or may	be an absolute
	   timeout in epoch seconds the	same as	would be used with
	   cond_timedwait().  Fractional seconds (e.g.,	2.5 seconds) are also
	   supported (to the extent of the underlying implementation).

	   If "TIMEOUT"	is missing, "undef", or	less than or equal to 0, then
	   this	call behaves the same as "dequeue_nb".

       ->pending()
	   Returns the number of items still in	the queue.  Returns "undef" if
	   the queue has been ended (see below), and there are no more items
	   in the queue.

       ->limit
	   Sets	the size of the	queue.	If set,	calls to "enqueue()" will
	   block until the number of pending items in the queue	drops below
	   the "limit".	 The "limit" does not prevent enqueuing	items beyond
	   that	count:

	    my $q = Thread::Queue->new(1, 2);
	    $q->limit =	4;
	    $q->enqueue(3, 4, 5);   # Does not block
	    $q->enqueue(6);	    # Blocks until at least 2 items are
				    # dequeued
	    my $size = $q->limit;   # Returns the current limit	(may return
				    # 'undef')
	    $q->limit =	0;	    # Queue size is now	unlimited

	   Calling any of the dequeue methods with "COUNT" greater than	a
	   queue's "limit" will	generate an error.

       ->end()
	   Declares that no more items will be added to	the queue.

	   All threads blocking	on "dequeue()" calls will be unblocked with
	   any remaining items in the queue and/or "undef" being returned.
	   Any subsequent calls	to "dequeue()" will behave like
	   "dequeue_nb()".

	   Once	ended, no more items may be placed 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 on	MetaCPAN: <https://metacpan.org/release/Thread-Queue>

       Code repository for CPAN	distribution:
       <https://github.com/Dual-Life/Thread-Queue>

       threads,	threads::shared

       Sample code in the examples directory of	this distribution on CPAN.

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 v5.28.3			  2020-05-14		      Thread::Queue(3)

NAME | VERSION | SYNOPSIS | DESCRIPTION | QUEUE CREATION | BASIC METHODS | ADVANCED METHODS | NOTES | LIMITATIONS | SEE ALSO | MAINTAINER | LICENSE

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