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Guido van Rossum27b7c7e2013-10-17 13:40:50 -07001"""Queues"""
2
3__all__ = ['Queue', 'PriorityQueue', 'LifoQueue', 'JoinableQueue',
4 'Full', 'Empty']
5
6import collections
7import heapq
8import queue
9
10from . import events
11from . import futures
12from . import locks
13from .tasks import coroutine
14
15
16# Re-export queue.Full and .Empty exceptions.
17Full = queue.Full
18Empty = queue.Empty
19
20
21class Queue:
22 """A queue, useful for coordinating producer and consumer coroutines.
23
24 If maxsize is less than or equal to zero, the queue size is infinite. If it
25 is an integer greater than 0, then "yield from put()" will block when the
26 queue reaches maxsize, until an item is removed by get().
27
28 Unlike the standard library Queue, you can reliably know this Queue's size
Victor Stinner2748bc72013-12-13 10:57:04 +010029 with qsize(), since your single-threaded asyncio application won't be
Guido van Rossum27b7c7e2013-10-17 13:40:50 -070030 interrupted between calling qsize() and doing an operation on the Queue.
31 """
32
33 def __init__(self, maxsize=0, *, loop=None):
34 if loop is None:
35 self._loop = events.get_event_loop()
36 else:
37 self._loop = loop
38 self._maxsize = maxsize
39
40 # Futures.
41 self._getters = collections.deque()
42 # Pairs of (item, Future).
43 self._putters = collections.deque()
44 self._init(maxsize)
45
46 def _init(self, maxsize):
47 self._queue = collections.deque()
48
49 def _get(self):
50 return self._queue.popleft()
51
52 def _put(self, item):
53 self._queue.append(item)
54
55 def __repr__(self):
56 return '<{} at {:#x} {}>'.format(
57 type(self).__name__, id(self), self._format())
58
59 def __str__(self):
60 return '<{} {}>'.format(type(self).__name__, self._format())
61
62 def _format(self):
63 result = 'maxsize={!r}'.format(self._maxsize)
64 if getattr(self, '_queue', None):
65 result += ' _queue={!r}'.format(list(self._queue))
66 if self._getters:
67 result += ' _getters[{}]'.format(len(self._getters))
68 if self._putters:
69 result += ' _putters[{}]'.format(len(self._putters))
70 return result
71
72 def _consume_done_getters(self):
73 # Delete waiters at the head of the get() queue who've timed out.
74 while self._getters and self._getters[0].done():
75 self._getters.popleft()
76
77 def _consume_done_putters(self):
78 # Delete waiters at the head of the put() queue who've timed out.
79 while self._putters and self._putters[0][1].done():
80 self._putters.popleft()
81
82 def qsize(self):
83 """Number of items in the queue."""
84 return len(self._queue)
85
86 @property
87 def maxsize(self):
88 """Number of items allowed in the queue."""
89 return self._maxsize
90
91 def empty(self):
92 """Return True if the queue is empty, False otherwise."""
93 return not self._queue
94
95 def full(self):
96 """Return True if there are maxsize items in the queue.
97
98 Note: if the Queue was initialized with maxsize=0 (the default),
99 then full() is never True.
100 """
101 if self._maxsize <= 0:
102 return False
103 else:
104 return self.qsize() == self._maxsize
105
106 @coroutine
107 def put(self, item):
108 """Put an item into the queue.
109
110 If you yield from put(), wait until a free slot is available
111 before adding item.
112 """
113 self._consume_done_getters()
114 if self._getters:
115 assert not self._queue, (
116 'queue non-empty, why are getters waiting?')
117
118 getter = self._getters.popleft()
119
120 # Use _put and _get instead of passing item straight to getter, in
121 # case a subclass has logic that must run (e.g. JoinableQueue).
122 self._put(item)
123 getter.set_result(self._get())
124
125 elif self._maxsize > 0 and self._maxsize == self.qsize():
126 waiter = futures.Future(loop=self._loop)
127
128 self._putters.append((item, waiter))
129 yield from waiter
130
131 else:
132 self._put(item)
133
134 def put_nowait(self, item):
135 """Put an item into the queue without blocking.
136
137 If no free slot is immediately available, raise Full.
138 """
139 self._consume_done_getters()
140 if self._getters:
141 assert not self._queue, (
142 'queue non-empty, why are getters waiting?')
143
144 getter = self._getters.popleft()
145
146 # Use _put and _get instead of passing item straight to getter, in
147 # case a subclass has logic that must run (e.g. JoinableQueue).
148 self._put(item)
149 getter.set_result(self._get())
150
151 elif self._maxsize > 0 and self._maxsize == self.qsize():
152 raise Full
153 else:
154 self._put(item)
155
156 @coroutine
157 def get(self):
158 """Remove and return an item from the queue.
159
160 If you yield from get(), wait until a item is available.
161 """
162 self._consume_done_putters()
163 if self._putters:
164 assert self.full(), 'queue not full, why are putters waiting?'
165 item, putter = self._putters.popleft()
166 self._put(item)
167
168 # When a getter runs and frees up a slot so this putter can
169 # run, we need to defer the put for a tick to ensure that
170 # getters and putters alternate perfectly. See
171 # ChannelTest.test_wait.
172 self._loop.call_soon(putter.set_result, None)
173
174 return self._get()
175
176 elif self.qsize():
177 return self._get()
178 else:
179 waiter = futures.Future(loop=self._loop)
180
181 self._getters.append(waiter)
182 return (yield from waiter)
183
184 def get_nowait(self):
185 """Remove and return an item from the queue.
186
Guido van Rossum16c42392013-11-24 22:41:35 -0800187 Return an item if one is immediately available, else raise Empty.
Guido van Rossum27b7c7e2013-10-17 13:40:50 -0700188 """
189 self._consume_done_putters()
190 if self._putters:
191 assert self.full(), 'queue not full, why are putters waiting?'
192 item, putter = self._putters.popleft()
193 self._put(item)
194 # Wake putter on next tick.
195 putter.set_result(None)
196
197 return self._get()
198
199 elif self.qsize():
200 return self._get()
201 else:
202 raise Empty
203
204
205class PriorityQueue(Queue):
206 """A subclass of Queue; retrieves entries in priority order (lowest first).
207
208 Entries are typically tuples of the form: (priority number, data).
209 """
210
211 def _init(self, maxsize):
212 self._queue = []
213
214 def _put(self, item, heappush=heapq.heappush):
215 heappush(self._queue, item)
216
217 def _get(self, heappop=heapq.heappop):
218 return heappop(self._queue)
219
220
221class LifoQueue(Queue):
222 """A subclass of Queue that retrieves most recently added entries first."""
223
224 def _init(self, maxsize):
225 self._queue = []
226
227 def _put(self, item):
228 self._queue.append(item)
229
230 def _get(self):
231 return self._queue.pop()
232
233
234class JoinableQueue(Queue):
235 """A subclass of Queue with task_done() and join() methods."""
236
237 def __init__(self, maxsize=0, *, loop=None):
238 super().__init__(maxsize=maxsize, loop=loop)
239 self._unfinished_tasks = 0
240 self._finished = locks.Event(loop=self._loop)
241 self._finished.set()
242
243 def _format(self):
244 result = Queue._format(self)
245 if self._unfinished_tasks:
246 result += ' tasks={}'.format(self._unfinished_tasks)
247 return result
248
249 def _put(self, item):
250 super()._put(item)
251 self._unfinished_tasks += 1
252 self._finished.clear()
253
254 def task_done(self):
255 """Indicate that a formerly enqueued task is complete.
256
257 Used by queue consumers. For each get() used to fetch a task,
258 a subsequent call to task_done() tells the queue that the processing
259 on the task is complete.
260
261 If a join() is currently blocking, it will resume when all items have
262 been processed (meaning that a task_done() call was received for every
263 item that had been put() into the queue).
264
265 Raises ValueError if called more times than there were items placed in
266 the queue.
267 """
268 if self._unfinished_tasks <= 0:
269 raise ValueError('task_done() called too many times')
270 self._unfinished_tasks -= 1
271 if self._unfinished_tasks == 0:
272 self._finished.set()
273
274 @coroutine
275 def join(self):
276 """Block until all items in the queue have been gotten and processed.
277
278 The count of unfinished tasks goes up whenever an item is added to the
279 queue. The count goes down whenever a consumer thread calls task_done()
280 to indicate that the item was retrieved and all work on it is complete.
281 When the count of unfinished tasks drops to zero, join() unblocks.
282 """
283 if self._unfinished_tasks > 0:
284 yield from self._finished.wait()