Use a custom timeout in test_support.open_urlresource.
[python.git] / Lib / Queue.py
blob2db8d76966535ac458d5f21ab5533dd4aca8297b
1 """A multi-producer, multi-consumer queue."""
3 from time import time as _time
4 try:
5 import threading as _threading
6 except ImportError:
7 import dummy_threading as _threading
8 from collections import deque
9 import heapq
11 __all__ = ['Empty', 'Full', 'Queue', 'PriorityQueue', 'LifoQueue']
13 class Empty(Exception):
14 "Exception raised by Queue.get(block=0)/get_nowait()."
15 pass
17 class Full(Exception):
18 "Exception raised by Queue.put(block=0)/put_nowait()."
19 pass
21 class Queue:
22 """Create a queue object with a given maximum size.
24 If maxsize is <= 0, the queue size is infinite.
25 """
26 def __init__(self, maxsize=0):
27 self.maxsize = maxsize
28 self._init(maxsize)
29 # mutex must be held whenever the queue is mutating. All methods
30 # that acquire mutex must release it before returning. mutex
31 # is shared between the three conditions, so acquiring and
32 # releasing the conditions also acquires and releases mutex.
33 self.mutex = _threading.Lock()
34 # Notify not_empty whenever an item is added to the queue; a
35 # thread waiting to get is notified then.
36 self.not_empty = _threading.Condition(self.mutex)
37 # Notify not_full whenever an item is removed from the queue;
38 # a thread waiting to put is notified then.
39 self.not_full = _threading.Condition(self.mutex)
40 # Notify all_tasks_done whenever the number of unfinished tasks
41 # drops to zero; thread waiting to join() is notified to resume
42 self.all_tasks_done = _threading.Condition(self.mutex)
43 self.unfinished_tasks = 0
45 def task_done(self):
46 """Indicate that a formerly enqueued task is complete.
48 Used by Queue consumer threads. For each get() used to fetch a task,
49 a subsequent call to task_done() tells the queue that the processing
50 on the task is complete.
52 If a join() is currently blocking, it will resume when all items
53 have been processed (meaning that a task_done() call was received
54 for every item that had been put() into the queue).
56 Raises a ValueError if called more times than there were items
57 placed in the queue.
58 """
59 self.all_tasks_done.acquire()
60 try:
61 unfinished = self.unfinished_tasks - 1
62 if unfinished <= 0:
63 if unfinished < 0:
64 raise ValueError('task_done() called too many times')
65 self.all_tasks_done.notify_all()
66 self.unfinished_tasks = unfinished
67 finally:
68 self.all_tasks_done.release()
70 def join(self):
71 """Blocks until all items in the Queue have been gotten and processed.
73 The count of unfinished tasks goes up whenever an item is added to the
74 queue. The count goes down whenever a consumer thread calls task_done()
75 to indicate the item was retrieved and all work on it is complete.
77 When the count of unfinished tasks drops to zero, join() unblocks.
78 """
79 self.all_tasks_done.acquire()
80 try:
81 while self.unfinished_tasks:
82 self.all_tasks_done.wait()
83 finally:
84 self.all_tasks_done.release()
86 def qsize(self):
87 """Return the approximate size of the queue (not reliable!)."""
88 self.mutex.acquire()
89 n = self._qsize()
90 self.mutex.release()
91 return n
93 def empty(self):
94 """Return True if the queue is empty, False otherwise (not reliable!)."""
95 self.mutex.acquire()
96 n = not self._qsize()
97 self.mutex.release()
98 return n
100 def full(self):
101 """Return True if the queue is full, False otherwise (not reliable!)."""
102 self.mutex.acquire()
103 n = 0 < self.maxsize == self._qsize()
104 self.mutex.release()
105 return n
107 def put(self, item, block=True, timeout=None):
108 """Put an item into the queue.
110 If optional args 'block' is true and 'timeout' is None (the default),
111 block if necessary until a free slot is available. If 'timeout' is
112 a positive number, it blocks at most 'timeout' seconds and raises
113 the Full exception if no free slot was available within that time.
114 Otherwise ('block' is false), put an item on the queue if a free slot
115 is immediately available, else raise the Full exception ('timeout'
116 is ignored in that case).
118 self.not_full.acquire()
119 try:
120 if self.maxsize > 0:
121 if not block:
122 if self._qsize() == self.maxsize:
123 raise Full
124 elif timeout is None:
125 while self._qsize() == self.maxsize:
126 self.not_full.wait()
127 elif timeout < 0:
128 raise ValueError("'timeout' must be a positive number")
129 else:
130 endtime = _time() + timeout
131 while self._qsize() == self.maxsize:
132 remaining = endtime - _time()
133 if remaining <= 0.0:
134 raise Full
135 self.not_full.wait(remaining)
136 self._put(item)
137 self.unfinished_tasks += 1
138 self.not_empty.notify()
139 finally:
140 self.not_full.release()
142 def put_nowait(self, item):
143 """Put an item into the queue without blocking.
145 Only enqueue the item if a free slot is immediately available.
146 Otherwise raise the Full exception.
148 return self.put(item, False)
150 def get(self, block=True, timeout=None):
151 """Remove and return an item from the queue.
153 If optional args 'block' is true and 'timeout' is None (the default),
154 block if necessary until an item is available. If 'timeout' is
155 a positive number, it blocks at most 'timeout' seconds and raises
156 the Empty exception if no item was available within that time.
157 Otherwise ('block' is false), return an item if one is immediately
158 available, else raise the Empty exception ('timeout' is ignored
159 in that case).
161 self.not_empty.acquire()
162 try:
163 if not block:
164 if not self._qsize():
165 raise Empty
166 elif timeout is None:
167 while not self._qsize():
168 self.not_empty.wait()
169 elif timeout < 0:
170 raise ValueError("'timeout' must be a positive number")
171 else:
172 endtime = _time() + timeout
173 while not self._qsize():
174 remaining = endtime - _time()
175 if remaining <= 0.0:
176 raise Empty
177 self.not_empty.wait(remaining)
178 item = self._get()
179 self.not_full.notify()
180 return item
181 finally:
182 self.not_empty.release()
184 def get_nowait(self):
185 """Remove and return an item from the queue without blocking.
187 Only get an item if one is immediately available. Otherwise
188 raise the Empty exception.
190 return self.get(False)
192 # Override these methods to implement other queue organizations
193 # (e.g. stack or priority queue).
194 # These will only be called with appropriate locks held
196 # Initialize the queue representation
197 def _init(self, maxsize):
198 self.queue = deque()
200 def _qsize(self, len=len):
201 return len(self.queue)
203 # Put a new item in the queue
204 def _put(self, item):
205 self.queue.append(item)
207 # Get an item from the queue
208 def _get(self):
209 return self.queue.popleft()
212 class PriorityQueue(Queue):
213 '''Variant of Queue that retrieves open entries in priority order (lowest first).
215 Entries are typically tuples of the form: (priority number, data).
218 def _init(self, maxsize):
219 self.queue = []
221 def _qsize(self, len=len):
222 return len(self.queue)
224 def _put(self, item, heappush=heapq.heappush):
225 heappush(self.queue, item)
227 def _get(self, heappop=heapq.heappop):
228 return heappop(self.queue)
231 class LifoQueue(Queue):
232 '''Variant of Queue that retrieves most recently added entries first.'''
234 def _init(self, maxsize):
235 self.queue = []
237 def _qsize(self, len=len):
238 return len(self.queue)
240 def _put(self, item):
241 self.queue.append(item)
243 def _get(self):
244 return self.queue.pop()