straw/Queue.py

   1 # This file is incorporated into Straw from Python 2.5 and retains the
   2 # license of Python, included in Straw as the file COPYING-python.
   3
   4 """A multi-producer, multi-consumer queue."""
   5
   6 from time import time as _time
   7 from collections import deque
   8
   9 __all__ = ['Empty', 'Full', 'Queue']
  10
  11 class Empty(Exception):
  12     "Exception raised by Queue.get(block=0)/get_nowait()."
  13     pass
  14
  15 class Full(Exception):
  16     "Exception raised by Queue.put(block=0)/put_nowait()."
  17     pass
  18
  19 class Queue:
  20     """Create a queue object with a given maximum size.
  21
  22     If maxsize is <= 0, the queue size is infinite.
  23     """
  24     def __init__(self, maxsize=0):
  25         try:
  26             import threading
  27         except ImportError:
  28             import dummy_threading as threading
  29         self._init(maxsize)
  30         # mutex must be held whenever the queue is mutating.  All methods
  31         # that acquire mutex must release it before returning.  mutex
  32         # is shared between the three conditions, so acquiring and
  33         # releasing the conditions also acquires and releases mutex.
  34         self.mutex = threading.Lock()
  35         # Notify not_empty whenever an item is added to the queue; a
  36         # thread waiting to get is notified then.
  37         self.not_empty = threading.Condition(self.mutex)
  38         # Notify not_full whenever an item is removed from the queue;
  39         # a thread waiting to put is notified then.
  40         self.not_full = threading.Condition(self.mutex)
  41         # Notify all_tasks_done whenever the number of unfinished tasks
  42         # drops to zero; thread waiting to join() is notified to resume
  43         self.all_tasks_done = threading.Condition(self.mutex)
  44         self.unfinished_tasks = 0
  45
  46     def task_done(self):
  47         """Indicate that a formerly enqueued task is complete.
  48
  49         Used by Queue consumer threads.  For each get() used to fetch a task,
  50         a subsequent call to task_done() tells the queue that the processing
  51         on the task is complete.
  52
  53         If a join() is currently blocking, it will resume when all items
  54         have been processed (meaning that a task_done() call was received
  55         for every item that had been put() into the queue).
  56
  57         Raises a ValueError if called more times than there were items
  58         placed in the queue.
  59         """
  60         self.all_tasks_done.acquire()
  61         try:
  62             unfinished = self.unfinished_tasks - 1
  63             if unfinished <= 0:
  64                 if unfinished < 0:
  65                     raise ValueError('task_done() called too many times')
  66                 self.all_tasks_done.notifyAll()
  67             self.unfinished_tasks = unfinished
  68         finally:
  69             self.all_tasks_done.release()
  70
  71     def join(self):
  72         """Blocks until all items in the Queue have been gotten and processed.
  73
  74         The count of unfinished tasks goes up whenever an item is added to the
  75         queue. The count goes down whenever a consumer thread calls task_done()
  76         to indicate the item was retrieved and all work on it is complete.
  77
  78         When the count of unfinished tasks drops to zero, join() unblocks.
  79         """
  80         self.all_tasks_done.acquire()
  81         try:
  82             while self.unfinished_tasks:
  83                 self.all_tasks_done.wait()
  84         finally:
  85             self.all_tasks_done.release()
  86
  87     def qsize(self):
  88         """Return the approximate size of the queue (not reliable!)."""
  89         self.mutex.acquire()
  90         n = self._qsize()
  91         self.mutex.release()
  92         return n
  93
  94     def empty(self):
  95         """Return True if the queue is empty, False otherwise (not reliable!)."""
  96         self.mutex.acquire()
  97         n = self._empty()
  98         self.mutex.release()
  99         return n
 100
 101     def full(self):
 102         """Return True if the queue is full, False otherwise (not reliable!)."""
 103         self.mutex.acquire()
 104         n = self._full()
 105         self.mutex.release()
 106         return n
 107
 108     def put(self, item, block=True, timeout=None):
 109         """Put an item into the queue.
 110
 111         If optional args 'block' is true and 'timeout' is None (the default),
 112         block if necessary until a free slot is available. If 'timeout' is
 113         a positive number, it blocks at most 'timeout' seconds and raises
 114         the Full exception if no free slot was available within that time.
 115         Otherwise ('block' is false), put an item on the queue if a free slot
 116         is immediately available, else raise the Full exception ('timeout'
 117         is ignored in that case).
 118         """
 119         self.not_full.acquire()
 120         try:
 121             if not block:
 122                 if self._full():
 123                     raise Full
 124             elif timeout is None:
 125                 while self._full():
 126                     self.not_full.wait()
 127             else:
 128                 if timeout < 0:
 129                     raise ValueError("'timeout' must be a positive number")
 130                 endtime = _time() + timeout
 131                 while self._full():
 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 self._empty():
 165                     raise Empty
 166             elif timeout is None:
 167                 while self._empty():
 168                     self.not_empty.wait()
 169             else:
 170                 if timeout < 0:
 171                     raise ValueError("'timeout' must be a positive number")
 172                 endtime = _time() + timeout
 173                 while self._empty():
 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.maxsize = maxsize
 199         self.queue = deque()
 200
 201     def _qsize(self):
 202         return len(self.queue)
 203
 204     # Check whether the queue is empty
 205     def _empty(self):
 206         return not self.queue
 207
 208     # Check whether the queue is full
 209     def _full(self):
 210         return self.maxsize > 0 and len(self.queue) == self.maxsize
 211
 212     # Put a new item in the queue
 213     def _put(self, item):
 214         self.queue.append(item)
 215
 216     # Get an item from the queue
 217     def _get(self):
 218         return self.queue.popleft()