gevent.queue – Synchronized queues

Synchronized queues.

The gevent.queue 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.

The classes in this module implement the iterator protocol. Iterating over a queue means repeatedly calling get until get returns StopIteration (specifically that class, not an instance or subclass).

>>> import gevent.queue
>>> queue = gevent.queue.Queue()
>>> queue.put(1)
>>> queue.put(2)
>>> queue.put(StopIteration)
>>> for item in queue:
...    print(item)
1
2

Changed in version 1.0: Queue(0) now means queue of infinite size, not a channel. A DeprecationWarning will be issued with this argument.

exception Empty

Bases: Exception

Exception raised by Queue.get(block=0)/get_nowait().

exception Full

Bases: Exception

Exception raised by Queue.put(block=0)/put_nowait().

class Channel(maxsize=1)

Bases: object

empty()

full()

get(block=True, timeout=None)

get_nowait()

next()

put(item, block=True, timeout=None)

put_nowait(item)

qsize()

property balance

getters

hub

putters

class JoinableQueue(maxsize=None, items=(), unfinished_tasks=None)

Bases: Queue

A subclass of Queue that additionally has task_done() and join() methods.

Changed in version 1.1a1: If unfinished_tasks is not given, then all the given items (if any) will be considered unfinished.

copy()

join(timeout=None)

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.

Parameters:

timeout (float) – If not None, then wait no more than this time in seconds for all tasks to finish.

Returns:

True if all tasks have finished; if timeout was given and expired before all tasks finished, False.

Changed in version 1.1a1: Add the timeout parameter.

task_done()

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.

unfinished_tasks

class LifoQueue(maxsize=None, items=(), _warn_depth=2)

Bases: Queue

A subclass of Queue that retrieves most recently added entries first.

class PriorityQueue(maxsize=None, items=(), _warn_depth=2)

Bases: Queue

A subclass of Queue that retrieves entries in priority order (lowest first).

Entries are typically tuples of the form: (priority number, data).

Changed in version 1.2a1: Any items given to the constructor will now be passed through heapq.heapify() to ensure the invariants of this class hold. Previously it was just assumed that they were already a heap.

class Queue(maxsize=None, items=(), _warn_depth=2)

Bases: object

Create a queue object with a given maximum size.

If maxsize is less than or equal to zero or None, the queue size is infinite.

Queues have a len equal to the number of items in them (the qsize()), but in a boolean context they are always True.

Changed in version 1.1b3: Queues now support len(); it behaves the same as qsize().

Changed in version 1.1b3: Multiple greenlets that block on a call to put() for a full queue will now be awakened to put their items into the queue in the order in which they arrived. Likewise, multiple greenlets that block on a call to get() for an empty queue will now receive items in the order in which they blocked. An implementation quirk under CPython usually ensured this was roughly the case previously anyway, but that wasn’t the case for PyPy.

copy()

empty()

Return True if the queue is empty, False otherwise.

full()

Return True if the queue is full, False otherwise.

Queue(None) is never full.

get(block=True, timeout=None)

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 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 Empty exception (timeout is ignored in that case).

get_nowait()

Remove and return an item from the queue without blocking.

Only get an item if one is immediately available. Otherwise raise the Empty exception.

next()

peek(block=True, timeout=None)

Return an item from the queue without removing it.

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 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 Empty exception (timeout is ignored in that case).

peek_nowait()

Return an item from the queue without blocking.

Only return an item if one is immediately available. Otherwise raise the Empty exception.

put(item, block=True, timeout=None)

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 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 Full exception (timeout is ignored in that case).

put_nowait(item)

Put an item into the queue without blocking.

Only enqueue the item if a free slot is immediately available. Otherwise raise the Full exception.

qsize()

Return the size of the queue.

getters

hub

property maxsize

putters

queue

SimpleQueue

alias of _PySimpleQueue

exception Full

An alias for Queue.Full

exception Empty

An alias for Queue.Empty

Examples

Example of how to wait for enqueued tasks to be completed:

def worker():
    while True:
        item = q.get()
        try:
            do_work(item)
        finally:
            q.task_done()

q = JoinableQueue()
for i in range(num_worker_threads):
     gevent.spawn(worker)

for item in source():
    q.put(item)

q.join()  # block until all tasks are done

Next page: gevent.local – Greenlet-local objects