cpython/Lib/queue.py at b2d9d134dcb5633deebebf2b0118cd4f7ca598a2 · python/cpython · GitHub

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'''A multi-producer, multi-consumer queue.'''

import threading

import types

from collections import deque

from heapq import heappush, heappop

from time import monotonic as time

try:

from _queue import SimpleQueue

except ImportError:

SimpleQueue = None

__all__ = ['Empty', 'Full', 'Queue', 'PriorityQueue', 'LifoQueue', 'SimpleQueue']

try:

from _queue import Empty

except ImportError:

class Empty(Exception):

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

pass

class Full(Exception):

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

pass

class ShutDown(Exception):

'''Raised when put/get with shut-down queue.'''

class Queue:

'''Create a queue object with a given maximum size.

If maxsize is <= 0, the queue size is infinite.

'''

def __init__(self, maxsize=0):

self.maxsize = maxsize

self._init(maxsize)

# 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

# Queue shutdown state

self.is_shutdown = False

def task_done(self):

'''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.

Raises ShutDown if the queue has been shut down immediately.

'''

with self.all_tasks_done:

unfinished = self.unfinished_tasks - 1

if unfinished <= 0:

if unfinished < 0:

raise ValueError('task_done() called too many times')

self.all_tasks_done.notify_all()

self.unfinished_tasks = unfinished

def join(self):

'''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.

Raises ShutDown if the queue has been shut down immediately.

'''

with self.all_tasks_done:

while self.unfinished_tasks:

self.all_tasks_done.wait()

def qsize(self):

'''Return the approximate size of the queue (not reliable!).'''

with self.mutex:

return self._qsize()

def empty(self):

'''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

qsize() can be used.

To create code that needs to wait for all queued tasks to be

completed, the preferred technique is to use the join() method.

'''

with self.mutex:

return not self._qsize()

def full(self):

'''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

qsize() can be used.

'''

with self.mutex:

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).

Raises ShutDown if the queue has been shut down.

'''

with self.not_full:

if self.is_shutdown:

raise ShutDown

if self.maxsize > 0:

if not block:

if self._qsize() >= self.maxsize:

raise Full

elif timeout is None:

while self._qsize() >= self.maxsize:

self.not_full.wait()

if self.is_shutdown:

raise ShutDown

elif timeout < 0:

raise ValueError("'timeout' must be a non-negative number")

else:

endtime = time() + timeout

while self._qsize() >= self.maxsize:

remaining = endtime - time()

if remaining <= 0.0:

raise Full

self.not_full.wait(remaining)

if self.is_shutdown:

raise ShutDown

self._put(item)

self.unfinished_tasks += 1

self.not_empty.notify()

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

in that case).

Raises ShutDown if the queue has been shut down and is empty,

or if the queue has been shut down immediately.

'''

with self.not_empty:

if self.is_shutdown and not self._qsize():

raise ShutDown

if not block:

if not self._qsize():

raise Empty

elif timeout is None:

while not self._qsize():

self.not_empty.wait()

if self.is_shutdown and not self._qsize():

raise ShutDown

elif timeout < 0:

raise ValueError("'timeout' must be a non-negative number")

else:

endtime = time() + timeout

while not self._qsize():

remaining = endtime - time()

if remaining <= 0.0:

raise Empty

self.not_empty.wait(remaining)

if self.is_shutdown and not self._qsize():

raise ShutDown

item = self._get()

self.not_full.notify()

return item

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)

def get_nowait(self):

'''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)

def shutdown(self, immediate=False):

'''Shut-down the queue, making queue gets and puts raise.

By default, gets will only raise once the queue is empty. Set

'immediate' to True to make gets raise immediately instead.

All blocked callers of put() will be unblocked, and also get()

and join() if 'immediate'. The ShutDown exception is raised.

'''

with self.mutex:

self.is_shutdown = True

if immediate:

n_items = self._qsize()

while self._qsize():

self._get()

if self.unfinished_tasks > 0:

self.unfinished_tasks -= 1

self.not_empty.notify_all()

# release all blocked threads in `join()`

self.all_tasks_done.notify_all()

self.not_full.notify_all()

# 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):

self.queue = deque()

def _qsize(self):

return len(self.queue)

# Put a new item in the queue

def _put(self, item):

self.queue.append(item)

# Get an item from the queue

def _get(self):

return self.queue.popleft()

__class_getitem__ = classmethod(types.GenericAlias)

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):

self.queue = []

def _qsize(self):

return len(self.queue)

def _put(self, item):

heappush(self.queue, item)

def _get(self):

return heappop(self.queue)

class LifoQueue(Queue):

'''Variant of Queue that retrieves most recently added entries first.'''

def _init(self, maxsize):

self.queue = []

def _qsize(self):

return len(self.queue)

def _put(self, item):

self.queue.append(item)

def _get(self):

return self.queue.pop()

class _PySimpleQueue:

'''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.

def __init__(self):

self._queue = deque()

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.

'''

self._queue.append(item)

self._count.release()

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

in that case).

'''

if timeout is not None and timeout < 0:

raise ValueError("'timeout' must be a non-negative number")

if not self._count.acquire(block, timeout):

raise Empty

return self._queue.popleft()

def put_nowait(self, item):

'''Put an item into the queue without blocking.

This is exactly equivalent to `put(item, block=False)` and is only provided

for compatibility with the Queue class.

'''

return self.put(item, block=False)

def get_nowait(self):

'''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)

def empty(self):

'''Return True if the queue is empty, False otherwise (not reliable!).'''

return len(self._queue) == 0

def qsize(self):

'''Return the approximate size of the queue (not reliable!).'''

return len(self._queue)

__class_getitem__ = classmethod(types.GenericAlias)

if SimpleQueue is None:

SimpleQueue = _PySimpleQueue

cpython/Lib/queue.py at b2d9d134dcb5633deebebf2b0118cd4f7ca598a2 · python/cpython · GitHub

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