19.5.8. Queues¶
Source code: Lib/asyncio/queues.py
Queues:
asyncio queue API was designed to be close to classes of the queue
module (Queue
, PriorityQueue
,
LifoQueue
), but it has no timeout parameter. The
asyncio.wait_for()
function can be used to cancel a task after a timeout.
19.5.8.1. Queue¶
-
class
asyncio.
Queue
(maxsize=0, *, loop=None)¶ A queue, useful for coordinating producer and consumer coroutines.
If maxsize is less than or equal to zero, the queue size is infinite. If it is an integer greater than
0
, thenawait put()
will block when the queue reaches maxsize, until an item is removed byget()
.Unlike the standard library
queue
, you can reliably know this Queue’s size withqsize()
, since your single-threaded asyncio application won’t be interrupted between callingqsize()
and doing an operation on the Queue.This class is not thread safe.
3.4.4 版更變: New
join()
andtask_done()
methods.-
empty
()¶ Return
True
if the queue is empty,False
otherwise.
-
full
()¶ Return
True
if there aremaxsize
items in the queue.備註
If the Queue was initialized with
maxsize=0
(the default), thenfull()
is neverTrue
.
-
coroutine
get
()¶ Remove and return an item from the queue. If queue is empty, wait until an item is available.
This method is a coroutine.
也參考
The
empty()
method.
-
get_nowait
()¶ Remove and return an item from the queue.
Return an item if one is immediately available, else raise
QueueEmpty
.
-
coroutine
join
()¶ 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.This method is a coroutine.
3.4.4 版新加入.
-
coroutine
put
(item)¶ Put an item into the queue. If the queue is full, wait until a free slot is available before adding item.
This method is a coroutine.
也參考
The
full()
method.
-
put_nowait
(item)¶ Put an item into the queue without blocking.
If no free slot is immediately available, raise
QueueFull
.
-
qsize
()¶ Number of items in the queue.
-
task_done
()¶ Indicate that a formerly enqueued task is complete.
Used by queue consumers. For each
get()
used to fetch a task, a subsequent call totask_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 atask_done()
call was received for every item that had beenput()
into the queue).Raises
ValueError
if called more times than there were items placed in the queue.3.4.4 版新加入.
-
maxsize
¶ Number of items allowed in the queue.
-
19.5.8.2. PriorityQueue¶
19.5.8.3. LifoQueue¶
19.5.8.3.1. Exceptions¶
-
exception
asyncio.
QueueEmpty
¶ Exception raised when the
get_nowait()
method is called on aQueue
object which is empty.
-
exception
asyncio.
QueueFull
¶ Exception raised when the
put_nowait()
method is called on aQueue
object which is full.