# cpython-withatomic / Lib / Queue.py

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151``` ```"""A multi-producer, multi-consumer 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. """ import 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 1 if the queue is empty, 0 otherwise (not reliable!).""" self.mutex.acquire() n = self._empty() self.mutex.release() return n def full(self): """Return 1 if the queue is full, 0 otherwise (not reliable!).""" self.mutex.acquire() n = self._full() self.mutex.release() return n def put(self, item, block=1): """Put an item into the queue. If optional arg 'block' is 1 (the default), block if necessary until a free slot is available. Otherwise (block is 0), put an item on the queue if a free slot is immediately available, else raise the Full exception. """ if block: self.fsema.acquire() 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, 0) def get(self, block=1): """Remove and return an item from the queue. If optional arg 'block' is 1 (the default), block if necessary until an item is available. Otherwise (block is 0), return an item if one is immediately available, else raise the Empty exception. """ if block: self.esema.acquire() 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(0) # 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): item = self.queue[0] del self.queue[0] return item ```