guv.queue
- greenthread-compatible queue¶Synchronized queues
This module implements multi-producer, multi-consumer queues that work across greenlets, with the
API similar to the classes found in the standard queue
and multiprocessing
modules.
A major difference is that queues in this module operate as channels when initialized with maxsize
of zero. In such case, both empty()
and full()
return
True
and put()
always blocks until a call to get()
retrieves the item.
An interesting difference, made possible because of GreenThreads, is that
qsize()
, empty()
, and full()
can be used
as indicators of whether the subsequent get()
or put()
will
not block. The new methods LightQueue.getting()
and LightQueue.putting()
report on
the number of GreenThreads blocking in put()
or get()
respectively.
guv.queue.
Full
[source]¶Bases: Exception
Exception raised by Queue.put(block=0)/put_nowait().
guv.queue.
Empty
[source]¶Bases: Exception
Exception raised by Queue.get(block=0)/get_nowait().
guv.queue.
Queue
(maxsize=None)[source]¶Bases: guv.queue.LightQueue
Create a queue object with a given maximum size
If maxsize is less than zero or None
, the queue size is infinite.
Queue(0)
is a channel, that is, its put()
method always blocks until the item is
delivered. (This is unlike the standard queue.Queue
, where 0 means infinite size).
In all other respects, this Queue class resembles the standard library, queue.Queue
.
join
() → None[source]¶Block until all items in the queue have been gotten and processed
The count of unfinished tasks goes up whenever an item is added to the queue.
The count goes down whenever a consumer thread calls task_done()
to indicate
that the item was retrieved and all work on it is complete. When the count of
unfinished tasks drops to zero, join()
unblocks.
task_done
() → None[source]¶Indicate that a formerly enqueued task is complete. Used by queue consumer threads.
For each get
used to fetch a task, a subsequent call to
task_done()
tells the queue
that the processing on the task is complete.
If a join()
is currently blocking, it will resume when all items have been processed
(meaning that a task_done()
call was received for every item that had been
put
into the queue).
Raises a ValueError
if called more times than there were items placed in the queue.
guv.queue.
PriorityQueue
(maxsize=None)[source]¶Bases: guv.queue.Queue
A subclass of Queue
that retrieves entries in priority order (lowest first)
Entries are typically tuples of the form: (priority number, data)
.
guv.queue.
LifoQueue
(maxsize=None)[source]¶Bases: guv.queue.Queue
A subclass of Queue
that retrieves most recently added entries first
guv.queue.
LightQueue
(maxsize=None)[source]¶Bases: object
This is a variant of Queue that behaves mostly like the standard Queue
. It differs by
not supporting the task_done()
or join()
methods, and is a
little faster for not having that overhead.
full
() → None[source]¶Return True
if the queue is full, False
otherwise.
Queue(None)
is never full.
get
(block=True, timeout=None) → None[source]¶Remove and return an item from the queue.
If optional args block is true and timeout is None
(the default),
block if necessary until an item is available. If timeout is a positive number,
it blocks at most timeout seconds and raises the queue.Empty
exception
if no item was available within that time. Otherwise (block is false), return
an item if one is immediately available, else raise the queue.Empty
exception
(timeout is ignored in that case).
get_nowait
() → None[source]¶Remove and return an item from the queue without blocking.
Only get an item if one is immediately available. Otherwise
raise the queue.Empty
exception.
getting
() → None[source]¶Returns the number of GreenThreads that are blocked waiting on an empty queue.
put
(item, block=True, timeout=None) → None[source]¶Put an item into the queue.
If optional arg block is true and timeout is None
(the default),
block if necessary until a free slot is available. If timeout is
a positive number, it blocks at most timeout seconds and raises
the queue.Full
exception if no free slot was available within that time.
Otherwise (block is false), put an item on the queue if a free slot
is immediately available, else raise the queue.Full
exception (timeout
is ignored in that case).
put_nowait
(item) → None[source]¶Put an item into the queue without blocking.
Only enqueue the item if a free slot is immediately available.
Otherwise raise the queue.Full
exception.