1'''A multi-producer, multi-consumer queue.'''
2
3try:
4    import threading
5except ImportError:
6    import dummy_threading as threading
7from collections import deque
8from heapq import heappush, heappop
9from time import monotonic as time
10
11__all__ = ['Empty', 'Full', 'Queue', 'PriorityQueue', 'LifoQueue']
12
13class Empty(Exception):
14    'Exception raised by Queue.get(block=0)/get_nowait().'
15    pass
16
17class Full(Exception):
18    'Exception raised by Queue.put(block=0)/put_nowait().'
19    pass
20
21class Queue:
22    '''Create a queue object with a given maximum size.
23
24    If maxsize is <= 0, the queue size is infinite.
25    '''
26
27    def __init__(self, maxsize=0):
28        self.maxsize = maxsize
29        self._init(maxsize)
30
31        # mutex must be held whenever the queue is mutating.  All methods
32        # that acquire mutex must release it before returning.  mutex
33        # is shared between the three conditions, so acquiring and
34        # releasing the conditions also acquires and releases mutex.
35        self.mutex = threading.Lock()
36
37        # Notify not_empty whenever an item is added to the queue; a
38        # thread waiting to get is notified then.
39        self.not_empty = threading.Condition(self.mutex)
40
41        # Notify not_full whenever an item is removed from the queue;
42        # a thread waiting to put is notified then.
43        self.not_full = threading.Condition(self.mutex)
44
45        # Notify all_tasks_done whenever the number of unfinished tasks
46        # drops to zero; thread waiting to join() is notified to resume
47        self.all_tasks_done = threading.Condition(self.mutex)
48        self.unfinished_tasks = 0
49
50    def task_done(self):
51        '''Indicate that a formerly enqueued task is complete.
52
53        Used by Queue consumer threads.  For each get() used to fetch a task,
54        a subsequent call to task_done() tells the queue that the processing
55        on the task is complete.
56
57        If a join() is currently blocking, it will resume when all items
58        have been processed (meaning that a task_done() call was received
59        for every item that had been put() into the queue).
60
61        Raises a ValueError if called more times than there were items
62        placed in the queue.
63        '''
64        with self.all_tasks_done:
65            unfinished = self.unfinished_tasks - 1
66            if unfinished <= 0:
67                if unfinished < 0:
68                    raise ValueError('task_done() called too many times')
69                self.all_tasks_done.notify_all()
70            self.unfinished_tasks = unfinished
71
72    def join(self):
73        '''Blocks until all items in the Queue have been gotten and processed.
74
75        The count of unfinished tasks goes up whenever an item is added to the
76        queue. The count goes down whenever a consumer thread calls task_done()
77        to indicate the item was retrieved and all work on it is complete.
78
79        When the count of unfinished tasks drops to zero, join() unblocks.
80        '''
81        with self.all_tasks_done:
82            while self.unfinished_tasks:
83                self.all_tasks_done.wait()
84
85    def qsize(self):
86        '''Return the approximate size of the queue (not reliable!).'''
87        with self.mutex:
88            return self._qsize()
89
90    def empty(self):
91        '''Return True if the queue is empty, False otherwise (not reliable!).
92
93        This method is likely to be removed at some point.  Use qsize() == 0
94        as a direct substitute, but be aware that either approach risks a race
95        condition where a queue can grow before the result of empty() or
96        qsize() can be used.
97
98        To create code that needs to wait for all queued tasks to be
99        completed, the preferred technique is to use the join() method.
100        '''
101        with self.mutex:
102            return not self._qsize()
103
104    def full(self):
105        '''Return True if the queue is full, False otherwise (not reliable!).
106
107        This method is likely to be removed at some point.  Use qsize() >= n
108        as a direct substitute, but be aware that either approach risks a race
109        condition where a queue can shrink before the result of full() or
110        qsize() can be used.
111        '''
112        with self.mutex:
113            return 0 < self.maxsize <= self._qsize()
114
115    def put(self, item, block=True, timeout=None):
116        '''Put an item into the queue.
117
118        If optional args 'block' is true and 'timeout' is None (the default),
119        block if necessary until a free slot is available. If 'timeout' is
120        a non-negative number, it blocks at most 'timeout' seconds and raises
121        the Full exception if no free slot was available within that time.
122        Otherwise ('block' is false), put an item on the queue if a free slot
123        is immediately available, else raise the Full exception ('timeout'
124        is ignored in that case).
125        '''
126        with self.not_full:
127            if self.maxsize > 0:
128                if not block:
129                    if self._qsize() >= self.maxsize:
130                        raise Full
131                elif timeout is None:
132                    while self._qsize() >= self.maxsize:
133                        self.not_full.wait()
134                elif timeout < 0:
135                    raise ValueError("'timeout' must be a non-negative number")
136                else:
137                    endtime = time() + timeout
138                    while self._qsize() >= self.maxsize:
139                        remaining = endtime - time()
140                        if remaining <= 0.0:
141                            raise Full
142                        self.not_full.wait(remaining)
143            self._put(item)
144            self.unfinished_tasks += 1
145            self.not_empty.notify()
146
147    def get(self, block=True, timeout=None):
148        '''Remove and return an item from the queue.
149
150        If optional args 'block' is true and 'timeout' is None (the default),
151        block if necessary until an item is available. If 'timeout' is
152        a non-negative number, it blocks at most 'timeout' seconds and raises
153        the Empty exception if no item was available within that time.
154        Otherwise ('block' is false), return an item if one is immediately
155        available, else raise the Empty exception ('timeout' is ignored
156        in that case).
157        '''
158        with self.not_empty:
159            if not block:
160                if not self._qsize():
161                    raise Empty
162            elif timeout is None:
163                while not self._qsize():
164                    self.not_empty.wait()
165            elif timeout < 0:
166                raise ValueError("'timeout' must be a non-negative number")
167            else:
168                endtime = time() + timeout
169                while not self._qsize():
170                    remaining = endtime - time()
171                    if remaining <= 0.0:
172                        raise Empty
173                    self.not_empty.wait(remaining)
174            item = self._get()
175            self.not_full.notify()
176            return item
177
178    def put_nowait(self, item):
179        '''Put an item into the queue without blocking.
180
181        Only enqueue the item if a free slot is immediately available.
182        Otherwise raise the Full exception.
183        '''
184        return self.put(item, block=False)
185
186    def get_nowait(self):
187        '''Remove and return an item from the queue without blocking.
188
189        Only get an item if one is immediately available. Otherwise
190        raise the Empty exception.
191        '''
192        return self.get(block=False)
193
194    # Override these methods to implement other queue organizations
195    # (e.g. stack or priority queue).
196    # These will only be called with appropriate locks held
197
198    # Initialize the queue representation
199    def _init(self, maxsize):
200        self.queue = deque()
201
202    def _qsize(self):
203        return len(self.queue)
204
205    # Put a new item in the queue
206    def _put(self, item):
207        self.queue.append(item)
208
209    # Get an item from the queue
210    def _get(self):
211        return self.queue.popleft()
212
213
214class PriorityQueue(Queue):
215    '''Variant of Queue that retrieves open entries in priority order (lowest first).
216
217    Entries are typically tuples of the form:  (priority number, data).
218    '''
219
220    def _init(self, maxsize):
221        self.queue = []
222
223    def _qsize(self):
224        return len(self.queue)
225
226    def _put(self, item):
227        heappush(self.queue, item)
228
229    def _get(self):
230        return heappop(self.queue)
231
232
233class LifoQueue(Queue):
234    '''Variant of Queue that retrieves most recently added entries first.'''
235
236    def _init(self, maxsize):
237        self.queue = []
238
239    def _qsize(self):
240        return len(self.queue)
241
242    def _put(self, item):
243        self.queue.append(item)
244
245    def _get(self):
246        return self.queue.pop()
247