Unix/Linux Go Back    


CentOS 7.0 - man page for thread::queue (centos section 3)

Linux & Unix Commands - Search Man Pages
Man Page or Keyword Search:   man
Select Man Page Set:       apropos Keyword Search (sections above)


Thread::Queue(3)	       User Contributed Perl Documentation		 Thread::Queue(3)

NAME
       Thread::Queue - Thread-safe queues

VERSION
       This document describes Thread::Queue version 3.02

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
	   }

	   # 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, c<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.

       ->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 Discussion Forum on CPAN: <http://www.cpanforum.com/dist/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 v5.16.3				    2013-02-19				 Thread::Queue(3)
Unix & Linux Commands & Man Pages : ©2000 - 2018 Unix and Linux Forums


All times are GMT -4. The time now is 11:29 PM.