queue — A synchronized queue class
https://docs.python.org/3.6/library/queue.html
https://github.com/python/cpython/blob/3.6/Lib/queue.py
The queue
module implements multi-producer, multi-consumer queues. It is especially useful in threaded programming when information must be exchanged safely between multiple threads. The Queue
class in this module implements all the required locking semantics. It depends on the availability of thread support in Python; see the threading
module.
The module implements three types of queue, which differ only in the order in which the entries are retrieved. In a FIFO queue, the first tasks added are the first retrieved. In a LIFO queue, the most recently added entry is the first retrieved (operating like a stack). With a priority queue, the entries are kept sorted (using the heapq
module) and the lowest valued entry is retrieved first.
Internally, the module uses locks to temporarily block competing threads; however, it is not designed to handle reentrancy within a thread.
The queue
module defines the following classes and exceptions:
- class
queue.
Queue
(maxsize=0) -
Constructor for a FIFO queue. maxsize is an integer that sets the upperbound limit on the number of items that can be placed in the queue. Insertion will block once this size has been reached, until queue items are consumed. If maxsize is less than or equal to zero, the queue size is infinite.
- class
queue.
LifoQueue
(maxsize=0) -
Constructor for a LIFO queue. maxsize is an integer that sets the upperbound limit on the number of items that can be placed in the queue. Insertion will block once this size has been reached, until queue items are consumed. If maxsize is less than or equal to zero, the queue size is infinite.
- class
queue.
PriorityQueue
(maxsize=0) -
Constructor for a priority queue. maxsize is an integer that sets the upperbound limit on the number of items that can be placed in the queue. Insertion will block once this size has been reached, until queue items are consumed. If maxsize is less than or equal to zero, the queue size is infinite.
The lowest valued entries are retrieved first (the lowest valued entry is the one returned by
sorted(list(entries))[0]
). A typical pattern for entries is a tuple in the form:(priority_number, data)
.
- exception
queue.
Empty
-
Exception raised when non-blocking
get()
(orget_nowait()
) is called on aQueue
object which is empty.
- exception
queue.
Full
-
Exception raised when non-blocking
put()
(orput_nowait()
) is called on aQueue
object which is full.
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