cpython/Lib/queue.py at 3.14 · python/cpython · GitHub [proxy]

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
'''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',
    'ShutDown',
    '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.
        '''
        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.
        '''
        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 ShutDown.

        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() and get() will be unblocked.

        If 'immediate', the queue is drained and unfinished tasks
        is reduced by the number of drained tasks.  If unfinished tasks
        is reduced to zero, callers of Queue.join are unblocked.
        '''
        with self.mutex:
            self.is_shutdown = True
            if immediate:
                while self._qsize():
                    self._get()
                    if self.unfinished_tasks > 0:
                        self.unfinished_tasks -= 1
                # release all blocked threads in `join()`
                self.all_tasks_done.notify_all()
            # All getters need to re-check queue-empty to raise ShutDown
            self.not_empty.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