'''A multi-producer, multi-consumer queue.'''
from collections import deque
from heapq import heappush, heappop
from time import monotonic as time
from _queue import SimpleQueue
__all__ = ['Empty', 'Full', 'Queue', 'PriorityQueue', 'LifoQueue', 'SimpleQueue']
'Exception raised by Queue.get(block=0)/get_nowait().'
'Exception raised by Queue.put(block=0)/put_nowait().'
'''Create a queue object with a given maximum size.
If maxsize is <= 0, the queue size is infinite.
def __init__(self, maxsize=0):
# mutex must be held whenever the queue is mutating. All methods
# that acquire mutex must release it before returning. mutex
# is shared between the three conditions, so acquiring and
# releasing the conditions also acquires and releases mutex.
self.mutex = threading.Lock()
# Notify not_empty whenever an item is added to the queue; a
# thread waiting to get is notified then.
self.not_empty = threading.Condition(self.mutex)
# Notify not_full whenever an item is removed from the queue;
# a thread waiting to put is notified then.
self.not_full = threading.Condition(self.mutex)
# Notify all_tasks_done whenever the number of unfinished tasks
# drops to zero; thread waiting to join() is notified to resume
self.all_tasks_done = threading.Condition(self.mutex)
self.unfinished_tasks = 0
'''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
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
with self.all_tasks_done:
unfinished = self.unfinished_tasks - 1
raise ValueError('task_done() called too many times')
self.all_tasks_done.notify_all()
self.unfinished_tasks = unfinished
'''Blocks 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 the item was retrieved and all work on it is complete.
When the count of unfinished tasks drops to zero, join() unblocks.
with self.all_tasks_done:
while self.unfinished_tasks:
self.all_tasks_done.wait()
'''Return the approximate size of the queue (not reliable!).'''
'''Return True if the queue is empty, False otherwise (not reliable!).
This method is likely to be removed at some point. Use qsize() == 0
as a direct substitute, but be aware that either approach risks a race
condition where a queue can grow before the result of empty() or
To create code that needs to wait for all queued tasks to be
completed, the preferred technique is to use the join() method.
'''Return True if the queue is full, False otherwise (not reliable!).
This method is likely to be removed at some point. Use qsize() >= n
as a direct substitute, but be aware that either approach risks a race
condition where a queue can shrink before the result of full() or
return 0 < self.maxsize <= self._qsize()
def put(self, item, block=True, timeout=None):
'''Put an item into the queue.
If optional args 'block' is true and 'timeout' is None (the default),
block if necessary until a free slot is available. If 'timeout' is
a non-negative 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).
if self._qsize() >= self.maxsize:
while self._qsize() >= self.maxsize:
raise ValueError("'timeout' must be a non-negative number")
endtime = time() + timeout
while self._qsize() >= self.maxsize:
remaining = endtime - time()
self.not_full.wait(remaining)
self.unfinished_tasks += 1
def get(self, 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 non-negative 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
raise ValueError("'timeout' must be a non-negative number")
endtime = time() + timeout
remaining = endtime - time()
self.not_empty.wait(remaining)
def put_nowait(self, 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.
return self.put(item, block=False)
'''Remove and return an item from the queue without blocking.
Only get an item if one is immediately available. Otherwise
raise the Empty exception.
return self.get(block=False)
# Override these methods to implement other queue organizations
# (e.g. stack or priority queue).
# These will only be called with appropriate locks held
# Initialize the queue representation
def _init(self, maxsize):
# Put a new item in the queue
# Get an item from the queue
return self.queue.popleft()
class PriorityQueue(Queue):
'''Variant of Queue that retrieves open entries in priority order (lowest first).
Entries are typically tuples of the form: (priority number, data).
def _init(self, maxsize):
heappush(self.queue, item)
return heappop(self.queue)
'''Variant of Queue that retrieves most recently added entries first.'''
def _init(self, maxsize):
'''Simple, unbounded FIFO queue.
This pure Python implementation is not reentrant.
# Note: while this pure Python version provides fairness
# (by using a threading.Semaphore which is itself fair, being based
# on threading.Condition), fairness is not part of the API contract.
# This allows the C version to use a different implementation.
self._count = threading.Semaphore(0)
def put(self, item, block=True, timeout=None):
'''Put the item on the queue.
The optional 'block' and 'timeout' arguments are ignored, as this method
never blocks. They are provided for compatibility with the Queue class.
def get(self, 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 non-negative 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
if timeout is not None and timeout < 0:
raise ValueError("'timeout' must be a non-negative number")
if not self._count.acquire(block, timeout):
return self._queue.popleft()
def put_nowait(self, item):
'''Put an item into the queue without blocking.
This is exactly equivalent to `put(item)` and is only provided
for compatibility with the Queue class.
return self.put(item, block=False)
'''Remove and return an item from the queue without blocking.
Only get an item if one is immediately available. Otherwise
raise the Empty exception.
return self.get(block=False)
'''Return True if the queue is empty, False otherwise (not reliable!).'''
return len(self._queue) == 0
'''Return the approximate size of the queue (not reliable!).'''
SimpleQueue = _PySimpleQueue
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