source file: /System/Library/Frameworks/Python.framework/Versions/2.3/lib/python2.3/Queue.py
file stats: 109 lines, 63 executed: 57.8% covered
   1. """A multi-producer, multi-consumer queue."""
   2. 
   3. from time import time as _time, sleep as _sleep
   4. 
   5. __all__ = ['Empty', 'Full', 'Queue']
   6. 
   7. class Empty(Exception):
   8.     "Exception raised by Queue.get(block=0)/get_nowait()."
   9.     pass
  10. 
  11. class Full(Exception):
  12.     "Exception raised by Queue.put(block=0)/put_nowait()."
  13.     pass
  14. 
  15. class Queue:
  16.     def __init__(self, maxsize=0):
  17.         """Initialize a queue object with a given maximum size.
  18. 
  19.         If maxsize is <= 0, the queue size is infinite.
  20.         """
  21.         try:
  22.             import thread
  23.         except ImportError:
  24.             import dummy_thread as thread
  25.         self._init(maxsize)
  26.         self.mutex = thread.allocate_lock()
  27.         self.esema = thread.allocate_lock()
  28.         self.esema.acquire()
  29.         self.fsema = thread.allocate_lock()
  30. 
  31.     def qsize(self):
  32.         """Return the approximate size of the queue (not reliable!)."""
  33.         self.mutex.acquire()
  34.         n = self._qsize()
  35.         self.mutex.release()
  36.         return n
  37. 
  38.     def empty(self):
  39.         """Return True if the queue is empty, False otherwise (not reliable!)."""
  40.         self.mutex.acquire()
  41.         n = self._empty()
  42.         self.mutex.release()
  43.         return n
  44. 
  45.     def full(self):
  46.         """Return True if the queue is full, False otherwise (not reliable!)."""
  47.         self.mutex.acquire()
  48.         n = self._full()
  49.         self.mutex.release()
  50.         return n
  51. 
  52.     def put(self, item, block=True, timeout=None):
  53.         """Put an item into the queue.
  54. 
  55.         If optional args 'block' is true and 'timeout' is None (the default),
  56.         block if necessary until a free slot is available. If 'timeout' is
  57.         a positive number, it blocks at most 'timeout' seconds and raises
  58.         the Full exception if no free slot was available within that time.
  59.         Otherwise ('block' is false), put an item on the queue if a free slot
  60.         is immediately available, else raise the Full exception ('timeout'
  61.         is ignored in that case).
  62.         """
  63.         if block:
  64.             if timeout is None:
  65.                 # blocking, w/o timeout, i.e. forever
  66.                 self.fsema.acquire()
  67.             elif timeout >= 0:
  68.                 # waiting max. 'timeout' seconds.
  69.                 # this code snipped is from threading.py: _Event.wait():
  70.                 # Balancing act:  We can't afford a pure busy loop, so we
  71.                 # have to sleep; but if we sleep the whole timeout time,
  72.                 # we'll be unresponsive.  The scheme here sleeps very
  73.                 # little at first, longer as time goes on, but never longer
  74.                 # than 20 times per second (or the timeout time remaining).
  75.                 delay = 0.0005 # 500 us -> initial delay of 1 ms
  76.                 endtime = _time() + timeout
  77.                 while True:
  78.                     if self.fsema.acquire(0):
  79.                         break
  80.                     remaining = endtime - _time()
  81.                     if remaining <= 0:  #time is over and no slot was free
  82.                         raise Full
  83.                     delay = min(delay * 2, remaining, .05)
  84.                     _sleep(delay)       #reduce CPU usage by using a sleep
  85.             else:
  86.                 raise ValueError("'timeout' must be a positive number")
  87.         elif not self.fsema.acquire(0):
  88.             raise Full
  89.         self.mutex.acquire()
  90.         release_fsema = True
  91.         try:
  92.             was_empty = self._empty()
  93.             self._put(item)
  94.             # If we fail before here, the empty state has
  95.             # not changed, so we can skip the release of esema
  96.             if was_empty:
  97.                 self.esema.release()
  98.             # If we fail before here, the queue can not be full, so
  99.             # release_full_sema remains True
 100.             release_fsema = not self._full()
 101.         finally:
 102.             # Catching system level exceptions here (RecursionDepth,
 103.             # OutOfMemory, etc) - so do as little as possible in terms
 104.             # of Python calls.
 105.             if release_fsema:
 106.                 self.fsema.release()
 107.             self.mutex.release()
 108. 
 109.     def put_nowait(self, item):
 110.         """Put an item into the queue without blocking.
 111. 
 112.         Only enqueue the item if a free slot is immediately available.
 113.         Otherwise raise the Full exception.
 114.         """
 115.         return self.put(item, False)
 116. 
 117.     def get(self, block=True, timeout=None):
 118.         """Remove and return an item from the queue.
 119. 
 120.         If optional args 'block' is true and 'timeout' is None (the default),
 121.         block if necessary until an item is available. If 'timeout' is
 122.         a positive number, it blocks at most 'timeout' seconds and raises
 123.         the Empty exception if no item was available within that time.
 124.         Otherwise ('block' is false), return an item if one is immediately
 125.         available, else raise the Empty exception ('timeout' is ignored
 126.         in that case).
 127.         """
 128.         if block:
 129.             if timeout is None:
 130.                 # blocking, w/o timeout, i.e. forever
 131.                 self.esema.acquire()
 132.             elif timeout >= 0:
 133.                 # waiting max. 'timeout' seconds.
 134.                 # this code snipped is from threading.py: _Event.wait():
 135.                 # Balancing act:  We can't afford a pure busy loop, so we
 136.                 # have to sleep; but if we sleep the whole timeout time,
 137.                 # we'll be unresponsive.  The scheme here sleeps very
 138.                 # little at first, longer as time goes on, but never longer
 139.                 # than 20 times per second (or the timeout time remaining).
 140.                 delay = 0.0005 # 500 us -> initial delay of 1 ms
 141.                 endtime = _time() + timeout
 142.                 while 1:
 143.                     if self.esema.acquire(0):
 144.                         break
 145.                     remaining = endtime - _time()
 146.                     if remaining <= 0:  #time is over and no element arrived
 147.                         raise Empty
 148.                     delay = min(delay * 2, remaining, .05)
 149.                     _sleep(delay)       #reduce CPU usage by using a sleep
 150.             else:
 151.                 raise ValueError("'timeout' must be a positive number")
 152.         elif not self.esema.acquire(0):
 153.             raise Empty
 154.         self.mutex.acquire()
 155.         release_esema = True
 156.         try:
 157.             was_full = self._full()
 158.             item = self._get()
 159.             # If we fail before here, the full state has
 160.             # not changed, so we can skip the release of fsema
 161.             if was_full:
 162.                 self.fsema.release()
 163.             # Failure means empty state also unchanged - release_esema
 164.             # remains True.
 165.             release_esema = not self._empty()
 166.         finally:
 167.             if release_esema:
 168.                 self.esema.release()
 169.             self.mutex.release()
 170.         return item
 171. 
 172.     def get_nowait(self):
 173.         """Remove and return an item from the queue without blocking.
 174. 
 175.         Only get an item if one is immediately available. Otherwise
 176.         raise the Empty exception.
 177.         """
 178.         return self.get(False)
 179. 
 180.     # Override these methods to implement other queue organizations
 181.     # (e.g. stack or priority queue).
 182.     # These will only be called with appropriate locks held
 183. 
 184.     # Initialize the queue representation
 185.     def _init(self, maxsize):
 186.         self.maxsize = maxsize
 187.         self.queue = []
 188. 
 189.     def _qsize(self):
 190.         return len(self.queue)
 191. 
 192.     # Check whether the queue is empty
 193.     def _empty(self):
 194.         return not self.queue
 195. 
 196.     # Check whether the queue is full
 197.     def _full(self):
 198.         return self.maxsize > 0 and len(self.queue) == self.maxsize
 199. 
 200.     # Put a new item in the queue
 201.     def _put(self, item):
 202.         self.queue.append(item)
 203. 
 204.     # Get an item from the queue
 205.     def _get(self):
 206.         return self.queue.pop(0)