"""A multi-producer, multi-consumer queue.""" from time import time as _time, sleep as _sleep class Empty(Exception): "Exception raised by Queue.get(block=0)/get_nowait()." pass class Full(Exception): "Exception raised by Queue.put(block=0)/put_nowait()." pass class Queue: def __init__(self, maxsize=0): """Initialize a queue object with a given maximum size. If maxsize is <= 0, the queue size is infinite. """ try: import thread except ImportError: import dummy_thread as thread self._init(maxsize) self.mutex = thread.allocate_lock() self.esema = thread.allocate_lock() self.esema.acquire() self.fsema = thread.allocate_lock() def qsize(self): """Return the approximate size of the queue (not reliable!).""" self.mutex.acquire() n = self._qsize() self.mutex.release() return n def empty(self): """Return True if the queue is empty, False otherwise (not reliable!).""" self.mutex.acquire() n = self._empty() self.mutex.release() return n def full(self): """Return True if the queue is full, False otherwise (not reliable!).""" self.mutex.acquire() n = self._full() self.mutex.release() return n def put(self, item, block=True, timeout=None): """Put an item into the queue. If optional args 'block' is true and 'timeout' is None (the default), block if necessary until a free slot is available. If 'timeout' is a positive number, it blocks at most 'timeout' seconds and raises the Full exception if no free slot was available within that time. Otherwise ('block' is false), put an item on the queue if a free slot is immediately available, else raise the Full exception ('timeout' is ignored in that case). """ if block: if timeout is None: # blocking, w/o timeout, i.e. forever self.fsema.acquire() elif timeout >= 0: # waiting max. 'timeout' seconds. # this code snipped is from threading.py: _Event.wait(): # Balancing act: We can't afford a pure busy loop, so we # have to sleep; but if we sleep the whole timeout time, # we'll be unresponsive. The scheme here sleeps very # little at first, longer as time goes on, but never longer # than 20 times per second (or the timeout time remaining). delay = 0.0005 # 500 us -> initial delay of 1 ms endtime = _time() + timeout while True: if self.fsema.acquire(0): break remaining = endtime - _time() if remaining <= 0: #time is over and no slot was free raise Full delay = min(delay * 2, remaining, .05) _sleep(delay) #reduce CPU usage by using a sleep else: raise ValueError("'timeout' must be a positive number") elif not self.fsema.acquire(0): raise Full self.mutex.acquire() release_fsema = True try: was_empty = self._empty() self._put(item) # If we fail before here, the empty state has # not changed, so we can skip the release of esema if was_empty: self.esema.release() # If we fail before here, the queue can not be full, so # release_full_sema remains True release_fsema = not self._full() finally: # Catching system level exceptions here (RecursionDepth, # OutOfMemory, etc) - so do as little as possible in terms # of Python calls. if release_fsema: self.fsema.release() self.mutex.release() def put_nowait(self, item): """Put an item into the queue without blocking. Only enqueue the item if a free slot is immediately available. Otherwise raise the Full exception. """ return self.put(item, False) def get(self, block=True, timeout=None): """Remove and return an item from the queue. If optional args 'block' is true and 'timeout' is None (the default), block if necessary until an item is available. If 'timeout' is a positive number, it blocks at most 'timeout' seconds and raises the Empty exception if no item was available within that time. Otherwise ('block' is false), return an item if one is immediately available, else raise the Empty exception ('timeout' is ignored in that case). """ if block: if timeout is None: # blocking, w/o timeout, i.e. forever self.esema.acquire() elif timeout >= 0: # waiting max. 'timeout' seconds. # this code snipped is from threading.py: _Event.wait(): # Balancing act: We can't afford a pure busy loop, so we # have to sleep; but if we sleep the whole timeout time, # we'll be unresponsive. The scheme here sleeps very # little at first, longer as time goes on, but never longer # than 20 times per second (or the timeout time remaining). delay = 0.0005 # 500 us -> initial delay of 1 ms endtime = _time() + timeout while 1: if self.esema.acquire(0): break remaining = endtime - _time() if remaining <= 0: #time is over and no element arrived raise Empty delay = min(delay * 2, remaining, .05) _sleep(delay) #reduce CPU usage by using a sleep else: raise ValueError("'timeout' must be a positive number") elif not self.esema.acquire(0): raise Empty self.mutex.acquire() release_esema = True try: was_full = self._full() item = self._get() # If we fail before here, the full state has # not changed, so we can skip the release of fsema if was_full: self.fsema.release() # Failure means empty state also unchanged - release_esema # remains True. release_esema = not self._empty() finally: if release_esema: self.esema.release() self.mutex.release() return item def get_nowait(self): """Remove and return an item from the queue without blocking. Only get an item if one is immediately available. Otherwise raise the Empty exception. """ return self.get(False) # Override these methods to implement other queue organizations # (e.g. stack or priority queue). # These will only be called with appropriate locks held # Initialize the queue representation def _init(self, maxsize): self.maxsize = maxsize self.queue = [] def _qsize(self): return len(self.queue) # Check whether the queue is empty def _empty(self): return not self.queue # Check whether the queue is full def _full(self): return self.maxsize > 0 and len(self.queue) == self.maxsize # Put a new item in the queue def _put(self, item): self.queue.append(item) # Get an item from the queue def _get(self): return self.queue.pop(0)