1 """A multi-producer, multi-consumer queue.""" 2 3 from time import time as _time 4 try: 5 import threading as _threading 6 except ImportError: 7 import dummy_threading as _threading 8 from collections import deque 9 import heapq 10 11 __all__ = ['Empty', 'Full', 'Queue', 'PriorityQueue', 'LifoQueue'] 12 13 class Empty(Exception): 14 "Exception raised by Queue.get(block=0)/get_nowait()." 15 pass 16 17 class Full(Exception): 18 "Exception raised by Queue.put(block=0)/put_nowait()." 19 pass 20 21 class Queue: 22 """Create a queue object with a given maximum size. 23 24 If maxsize is <= 0, the queue size is infinite. 25 """ 26 def __init__(self, maxsize=0): 27 self.maxsize = maxsize 28 self._init(maxsize) 29 # mutex must be held whenever the queue is mutating. All methods 30 # that acquire mutex must release it before returning. mutex 31 # is shared between the three conditions, so acquiring and 32 # releasing the conditions also acquires and releases mutex. 33 self.mutex = _threading.Lock() 34 # Notify not_empty whenever an item is added to the queue; a 35 # thread waiting to get is notified then. 36 self.not_empty = _threading.Condition(self.mutex) 37 # Notify not_full whenever an item is removed from the queue; 38 # a thread waiting to put is notified then. 39 self.not_full = _threading.Condition(self.mutex) 40 # Notify all_tasks_done whenever the number of unfinished tasks 41 # drops to zero; thread waiting to join() is notified to resume 42 self.all_tasks_done = _threading.Condition(self.mutex) 43 self.unfinished_tasks = 0 44 45 def task_done(self): 46 """Indicate that a formerly enqueued task is complete. 47 48 Used by Queue consumer threads. For each get() used to fetch a task, 49 a subsequent call to task_done() tells the queue that the processing 50 on the task is complete. 51 52 If a join() is currently blocking, it will resume when all items 53 have been processed (meaning that a task_done() call was received 54 for every item that had been put() into the queue). 55 56 Raises a ValueError if called more times than there were items 57 placed in the queue. 58 """ 59 self.all_tasks_done.acquire() 60 try: 61 unfinished = self.unfinished_tasks - 1 62 if unfinished <= 0: 63 if unfinished < 0: 64 raise ValueError('task_done() called too many times') 65 self.all_tasks_done.notify_all() 66 self.unfinished_tasks = unfinished 67 finally: 68 self.all_tasks_done.release() 69 70 def join(self): 71 """Blocks until all items in the Queue have been gotten and processed. 72 73 The count of unfinished tasks goes up whenever an item is added to the 74 queue. The count goes down whenever a consumer thread calls task_done() 75 to indicate the item was retrieved and all work on it is complete. 76 77 When the count of unfinished tasks drops to zero, join() unblocks. 78 """ 79 self.all_tasks_done.acquire() 80 try: 81 while self.unfinished_tasks: 82 self.all_tasks_done.wait() 83 finally: 84 self.all_tasks_done.release() 85 86 def qsize(self): 87 """Return the approximate size of the queue (not reliable!).""" 88 self.mutex.acquire() 89 n = self._qsize() 90 self.mutex.release() 91 return n 92 93 def empty(self): 94 """Return True if the queue is empty, False otherwise (not reliable!).""" 95 self.mutex.acquire() 96 n = not self._qsize() 97 self.mutex.release() 98 return n 99 100 def full(self): 101 """Return True if the queue is full, False otherwise (not reliable!).""" 102 self.mutex.acquire() 103 n = 0 < self.maxsize == self._qsize() 104 self.mutex.release() 105 return n 106 107 def put(self, item, block=True, timeout=None): 108 """Put an item into the queue. 109 110 If optional args 'block' is true and 'timeout' is None (the default), 111 block if necessary until a free slot is available. If 'timeout' is 112 a positive number, it blocks at most 'timeout' seconds and raises 113 the Full exception if no free slot was available within that time. 114 Otherwise ('block' is false), put an item on the queue if a free slot 115 is immediately available, else raise the Full exception ('timeout' 116 is ignored in that case). 117 """ 118 self.not_full.acquire() 119 try: 120 if self.maxsize > 0: 121 if not block: 122 if self._qsize() == self.maxsize: 123 raise Full 124 elif timeout is None: 125 while self._qsize() == self.maxsize: 126 self.not_full.wait() 127 elif timeout < 0: 128 raise ValueError("'timeout' must be a positive number") 129 else: 130 endtime = _time() + timeout 131 while self._qsize() == self.maxsize: 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 not self._qsize(): 165 raise Empty 166 elif timeout is None: 167 while not self._qsize(): 168 self.not_empty.wait() 169 elif timeout < 0: 170 raise ValueError("'timeout' must be a positive number") 171 else: 172 endtime = _time() + timeout 173 while not self._qsize(): 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.queue = deque() 199 200 def _qsize(self, len=len): 201 return len(self.queue) 202 203 # Put a new item in the queue 204 def _put(self, item): 205 self.queue.append(item) 206 207 # Get an item from the queue 208 def _get(self): 209 return self.queue.popleft() 210 211 212 class PriorityQueue(Queue): 213 '''Variant of Queue that retrieves open entries in priority order (lowest first). 214 215 Entries are typically tuples of the form: (priority number, data). 216 ''' 217 218 def _init(self, maxsize): 219 self.queue = [] 220 221 def _qsize(self, len=len): 222 return len(self.queue) 223 224 def _put(self, item, heappush=heapq.heappush): 225 heappush(self.queue, item) 226 227 def _get(self, heappop=heapq.heappop): 228 return heappop(self.queue) 229 230 231 class LifoQueue(Queue): 232 '''Variant of Queue that retrieves most recently added entries first.''' 233 234 def _init(self, maxsize): 235 self.queue = [] 236 237 def _qsize(self, len=len): 238 return len(self.queue) 239 240 def _put(self, item): 241 self.queue.append(item) 242 243 def _get(self): 244 return self.queue.pop() 245
