| """A multi-producer, multi-consumer queue.""" |
| |
| from time import time as _time, sleep as _sleep |
| |
| __all__ = ['Empty', 'Full', 'Queue'] |
| |
| 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) |