---
name: "Thread::Queue-5.005"
section: "3pm"
platform: "linux"
package: "perl-5.005-thread"
version: "5.005.03-7.1"
release: "Debian 2.2 (Potato)"
platforms: ["linux"]
url: "https://new.carta.tech/Thread::Queue-5.005"
---

# Thread::Queue-5.005(3pm)

thread-safe queues

## NAME

Thread::Queue - thread-safe queues

## SYNOPSIS

```
    use Thread::Queue;
    my $q = new Thread::Queue;
    $q->enqueue("foo", "bar");
    my $foo = $q->dequeue;    # The "bar" is still in the queue.
    my $foo = $q->dequeue_nb; # returns "bar", or undef if the queue was
                              # empty
    my $left = $q->pending;   # returns the number of items still in the queue
```

## DESCRIPTION

A queue, as implemented by `Thread::Queue` is a thread-safe data structure much like a list. Any number of threads can safely add elements to the end of the list, or remove elements from the head of the list. (Queues don't permit adding or removing elements from the middle of the list)

## FUNCTIONS AND METHODS

- new

  The `new` function creates a new empty queue.\

- enqueue LIST

  The `enqueue` method adds a list of scalars on to the end of the queue. The queue will grow as needed to accomodate the list.\

- dequeue

  The `dequeue` method removes a scalar from the head of the queue and returns it. If the queue is currently empty, `dequeue` will block the thread until another thread `enqueue`s a scalar.\

- dequeue\_nb

  The `dequeue_nb` method, like the `dequeue` method, removes a scalar from the head of the queue and returns it. Unlike `dequeue`, though, `dequeue_nb` won't block if the queue is empty, instead returning `undef`.\

- pending

  The `pending` method returns the number of items still in the queue.  (If there can be multiple readers on the queue it's best to lock the queue before checking to make sure that it stays in a consistent state)

## SEE ALSO

the *Thread* manpage

\=cut

sub new {\
     my `$class` = shift;\
     return bless \[@\_\], `$class`; }

sub dequeue {\
     use attrs *qw*(locked method);\
     my `$q` = shift;\
     cond\_wait `$q` until @$q;\
     return shift @$q; }

sub dequeue\_nb {\
   use attrs *qw*(locked method);\
   my `$q` = shift;\
   if (@$q) {\
     return shift @$q;\
   } else {\
     return undef;\
   } }

sub enqueue {\
     use attrs *qw*(locked method);\
     my `$q` = shift;\
     *push*(@$q, `@_`) and cond\_broadcast `$q`; }

sub pending {\
   use attrs *qw*(locked method);\
   my `$q` = shift;\
   return *scalar*(@$q); }

1;