Mercurial > cpython-lru_cache-weakref

annotate Lib/queue.py @ 83447:678564fc0962 3.3

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#17789: test_random now works with unittest test discovery. Patch by Zachary Ware.
author Ezio Melotti <ezio.melotti@gmail.com>
date Fri, 19 Apr 2013 05:45:27 +0300
parents 76d2e0761d18
children 2122d56d6bc5 8d28d44f3a9a
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1 '''A multi-producer, multi-consumer queue.'''
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2
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3 try:
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4 import threading
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5 except ImportError:
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6 import dummy_threading as threading
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7 from collections import deque
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8 from heapq import heappush, heappop
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9 try:
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10 from time import monotonic as time
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11 except ImportError:
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12 from time import time
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13
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14 __all__ = ['Empty', 'Full', 'Queue', 'PriorityQueue', 'LifoQueue']
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15
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16 class Empty(Exception):
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17 'Exception raised by Queue.get(block=0)/get_nowait().'
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18 pass
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19
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20 class Full(Exception):
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21 'Exception raised by Queue.put(block=0)/put_nowait().'
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22 pass
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23
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24 class Queue:
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25 '''Create a queue object with a given maximum size.
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26
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27 If maxsize is <= 0, the queue size is infinite.
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28 '''
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29
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30 def __init__(self, maxsize=0):
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31 self.maxsize = maxsize
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32 self._init(maxsize)
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33
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34 # mutex must be held whenever the queue is mutating. All methods
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35 # that acquire mutex must release it before returning. mutex
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36 # is shared between the three conditions, so acquiring and
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37 # releasing the conditions also acquires and releases mutex.
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38 self.mutex = threading.Lock()
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39
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40 # Notify not_empty whenever an item is added to the queue; a
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41 # thread waiting to get is notified then.
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42 self.not_empty = threading.Condition(self.mutex)
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43
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44 # Notify not_full whenever an item is removed from the queue;
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45 # a thread waiting to put is notified then.
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46 self.not_full = threading.Condition(self.mutex)
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47
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48 # Notify all_tasks_done whenever the number of unfinished tasks
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49 # drops to zero; thread waiting to join() is notified to resume
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50 self.all_tasks_done = threading.Condition(self.mutex)
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51 self.unfinished_tasks = 0
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52
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53 def task_done(self):
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54 '''Indicate that a formerly enqueued task is complete.
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55
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56 Used by Queue consumer threads. For each get() used to fetch a task,
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57 a subsequent call to task_done() tells the queue that the processing
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58 on the task is complete.
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59
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60 If a join() is currently blocking, it will resume when all items
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61 have been processed (meaning that a task_done() call was received
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62 for every item that had been put() into the queue).
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63
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64 Raises a ValueError if called more times than there were items
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65 placed in the queue.
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66 '''
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67 with self.all_tasks_done:
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68 unfinished = self.unfinished_tasks - 1
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69 if unfinished <= 0:
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70 if unfinished < 0:
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71 raise ValueError('task_done() called too many times')
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72 self.all_tasks_done.notify_all()
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73 self.unfinished_tasks = unfinished
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74
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75 def join(self):
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76 '''Blocks until all items in the Queue have been gotten and processed.
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77
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78 The count of unfinished tasks goes up whenever an item is added to the
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79 queue. The count goes down whenever a consumer thread calls task_done()
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80 to indicate the item was retrieved and all work on it is complete.
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81
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82 When the count of unfinished tasks drops to zero, join() unblocks.
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83 '''
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84 with self.all_tasks_done:
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85 while self.unfinished_tasks:
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86 self.all_tasks_done.wait()
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87
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88 def qsize(self):
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89 '''Return the approximate size of the queue (not reliable!).'''
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90 with self.mutex:
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91 return self._qsize()
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92
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93 def empty(self):
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94 '''Return True if the queue is empty, False otherwise (not reliable!).
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95
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96 This method is likely to be removed at some point. Use qsize() == 0
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97 as a direct substitute, but be aware that either approach risks a race
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98 condition where a queue can grow before the result of empty() or
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99 qsize() can be used.
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100
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101 To create code that needs to wait for all queued tasks to be
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102 completed, the preferred technique is to use the join() method.
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103 '''
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104 with self.mutex:
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105 return not self._qsize()
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106
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107 def full(self):
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108 '''Return True if the queue is full, False otherwise (not reliable!).
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109
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110 This method is likely to be removed at some point. Use qsize() >= n
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111 as a direct substitute, but be aware that either approach risks a race
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112 condition where a queue can shrink before the result of full() or
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113 qsize() can be used.
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114 '''
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115 with self.mutex:
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116 return 0 < self.maxsize <= self._qsize()
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117
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118 def put(self, item, block=True, timeout=None):
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119 '''Put an item into the queue.
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120
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121 If optional args 'block' is true and 'timeout' is None (the default),
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122 block if necessary until a free slot is available. If 'timeout' is
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123 a positive number, it blocks at most 'timeout' seconds and raises
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124 the Full exception if no free slot was available within that time.
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125 Otherwise ('block' is false), put an item on the queue if a free slot
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126 is immediately available, else raise the Full exception ('timeout'
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127 is ignored in that case).
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128 '''
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129 with self.not_full:
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130 if self.maxsize > 0:
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131 if not block:
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132 if self._qsize() >= self.maxsize:
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133 raise Full
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134 elif timeout is None:
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135 while self._qsize() >= self.maxsize:
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136 self.not_full.wait()
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137 elif timeout < 0:
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138 raise ValueError("'timeout' must be a positive number")
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139 else:
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140 endtime = time() + timeout
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141 while self._qsize() >= self.maxsize:
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142 remaining = endtime - time()
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143 if remaining <= 0.0:
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144 raise Full
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145 self.not_full.wait(remaining)
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146 self._put(item)
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147 self.unfinished_tasks += 1
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148 self.not_empty.notify()
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149
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150 def get(self, block=True, timeout=None):
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151 '''Remove and return an item from the queue.
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152
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153 If optional args 'block' is true and 'timeout' is None (the default),
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154 block if necessary until an item is available. If 'timeout' is
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155 a positive number, it blocks at most 'timeout' seconds and raises
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156 the Empty exception if no item was available within that time.
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157 Otherwise ('block' is false), return an item if one is immediately
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158 available, else raise the Empty exception ('timeout' is ignored
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159 in that case).
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160 '''
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161 with self.not_empty:
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162 if not block:
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163 if not self._qsize():
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164 raise Empty
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165 elif timeout is None:
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166 while not self._qsize():
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167 self.not_empty.wait()
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168 elif timeout < 0:
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169 raise ValueError("'timeout' must be a positive number")
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170 else:
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171 endtime = time() + timeout
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172 while not self._qsize():
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173 remaining = endtime - time()
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174 if remaining <= 0.0:
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175 raise Empty
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176 self.not_empty.wait(remaining)
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177 item = self._get()
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178 self.not_full.notify()
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179 return item
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180
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181 def put_nowait(self, item):
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182 '''Put an item into the queue without blocking.
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183
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184 Only enqueue the item if a free slot is immediately available.
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185 Otherwise raise the Full exception.
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186 '''
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187 return self.put(item, block=False)
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188
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189 def get_nowait(self):
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190 '''Remove and return an item from the queue without blocking.
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191
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192 Only get an item if one is immediately available. Otherwise
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193 raise the Empty exception.
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194 '''
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195 return self.get(block=False)
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196
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197 # Override these methods to implement other queue organizations
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198 # (e.g. stack or priority queue).
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199 # These will only be called with appropriate locks held
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200
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201 # Initialize the queue representation
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202 def _init(self, maxsize):
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203 self.queue = deque()
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204
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205 def _qsize(self):
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206 return len(self.queue)
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207
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208 # Put a new item in the queue
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209 def _put(self, item):
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210 self.queue.append(item)
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211
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212 # Get an item from the queue
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213 def _get(self):
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214 return self.queue.popleft()
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215
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216
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217 class PriorityQueue(Queue):
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218 '''Variant of Queue that retrieves open entries in priority order (lowest first).
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219
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220 Entries are typically tuples of the form: (priority number, data).
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221 '''
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222
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223 def _init(self, maxsize):
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224 self.queue = []
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225
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226 def _qsize(self):
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227 return len(self.queue)
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228
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229 def _put(self, item):
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230 heappush(self.queue, item)
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231
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232 def _get(self):
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233 return heappop(self.queue)
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234
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235
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236 class LifoQueue(Queue):
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237 '''Variant of Queue that retrieves most recently added entries first.'''
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238
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239 def _init(self, maxsize):
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240 self.queue = []
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241
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242 def _qsize(self):
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243 return len(self.queue)
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244
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245 def _put(self, item):
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246 self.queue.append(item)
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247
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248 def _get(self):
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249 return self.queue.pop()