Lib/Queue.py

   1 """A multi-producer, multi-consumer queue."""
   2
   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
  10
  11 __all__ = ['Empty', 'Full', 'Queue', 'PriorityQueue', 'LifoQueue']
  12
  13 class Empty(Exception):
  14     "Exception raised by Queue.get(block=0)/get_nowait()."
  15     pass
  16
  17 class Full(Exception):
  18     "Exception raised by Queue.put(block=0)/put_nowait()."
  19     pass
  20
  21 class Queue:
  22     """Create a queue object with a given maximum size.
  23
  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
  44
  45     def task_done(self):
  46         """Indicate that a formerly enqueued task is complete.
  47
  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.
  51
  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).
  55
  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()
  69
  70     def join(self):
  71         """Blocks until all items in the Queue have been gotten and processed.
  72
  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.
  76
  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()
  85
  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
  92
  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
  99
 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
 106
 107     def put(self, item, block=True, timeout=None):
 108         """Put an item into the queue.
 109
 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).
 117         """
 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()
 141
 142     def put_nowait(self, item):
 143         """Put an item into the queue without blocking.
 144
 145         Only enqueue the item if a free slot is immediately available.
 146         Otherwise raise the Full exception.
 147         """
 148         return self.put(item, False)
 149
 150     def get(self, block=True, timeout=None):
 151         """Remove and return an item from the queue.
 152
 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).
 160         """
 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()
 183
 184     def get_nowait(self):
 185         """Remove and return an item from the queue without blocking.
 186
 187         Only get an item if one is immediately available. Otherwise
 188         raise the Empty exception.
 189         """
 190         return self.get(False)
 191
 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
 195
 196     # Initialize the queue representation
 197     def _init(self, maxsize):
 198         self.queue = deque()
 199
 200     def _qsize(self, len=len):
 201         return len(self.queue)
 202
 203     # Put a new item in the queue
 204     def _put(self, item):
 205         self.queue.append(item)
 206
 207     # Get an item from the queue
 208     def _get(self):
 209         return self.queue.popleft()
 210
 211
 212 class PriorityQueue(Queue):
 213     '''Variant of Queue that retrieves open entries in priority order (lowest first).
 214
 215     Entries are typically tuples of the form:  (priority number, data).
 216     '''
 217
 218     def _init(self, maxsize):
 219         self.queue = []
 220
 221     def _qsize(self, len=len):
 222         return len(self.queue)
 223
 224     def _put(self, item, heappush=heapq.heappush):
 225         heappush(self.queue, item)
 226
 227     def _get(self, heappop=heapq.heappop):
 228         return heappop(self.queue)
 229
 230
 231 class LifoQueue(Queue):
 232     '''Variant of Queue that retrieves most recently added entries first.'''
 233
 234     def _init(self, maxsize):
 235         self.queue = []
 236
 237     def _qsize(self, len=len):
 238         return len(self.queue)
 239
 240     def _put(self, item):
 241         self.queue.append(item)
 242
 243     def _get(self):
 244         return self.queue.pop()