Mercurial > cpython-lru_cache-weakref

annotate Lib/Queue.py @ 4566:6403c94de50d legacy-trunk

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Added safeguard against failure in __del__.
author Guido van Rossum <guido@python.org>
date Wed, 27 Nov 1996 19:39:58 +0000
parents 305748ebab43
children 4b2d8dc92db4
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f025eef93130 New module implementing a multi-everything queue.
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1 # A multi-producer, multi-consumer queue.
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2
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3 Empty = 'Queue.Empty' # Exception raised by get_nowait()
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4
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5 class Queue:
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6
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7 # Initialize a queue object with a given maximum size
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8 # (If maxsize is <= 0, the maximum size is infinite)
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560ec7030817 * Mass change: get rid of all init() methods, in favor of __init__()
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9 def __init__(self, maxsize):
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10 import thread
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11 self._init(maxsize)
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12 self.mutex = thread.allocate_lock()
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13 self.esema = thread.allocate_lock()
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14 self.esema.acquire_lock()
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15 self.fsema = thread.allocate_lock()
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16
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17 # Get an approximation of the queue size (not reliable!)
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18 def qsize(self):
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19 self.mutex.acquire_lock()
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20 n = self._qsize()
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21 self.mutex.release_lock()
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22 return n
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23
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24 # Check if the queue is empty (not reliable!)
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25 def empty(self):
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26 self.mutex.acquire_lock()
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27 n = self._empty()
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28 self.mutex.release_lock()
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29 return n
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30
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31 # Check if the queue is full (not reliable!)
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32 def full(self):
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33 self.mutex.acquire_lock()
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34 n = self._full()
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35 self.mutex.release_lock()
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36 return n
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37
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38 # Put a new item into the queue
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39 def put(self, item):
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40 self.fsema.acquire_lock()
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41 self.mutex.acquire_lock()
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42 was_empty = self._empty()
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43 self._put(item)
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44 if was_empty:
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45 self.esema.release_lock()
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46 if not self._full():
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47 self.fsema.release_lock()
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48 self.mutex.release_lock()
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49
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50 # Get an item from the queue,
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51 # blocking if necessary until one is available
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52 def get(self):
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53 self.esema.acquire_lock()
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54 self.mutex.acquire_lock()
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55 was_full = self._full()
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56 item = self._get()
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57 if was_full:
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58 self.fsema.release_lock()
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59 if not self._empty():
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60 self.esema.release_lock()
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61 self.mutex.release_lock()
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62 return item
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63
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64 # Get an item from the queue if one is immediately available,
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65 # raise Empty if the queue is empty or temporarily unavailable
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66 def get_nowait(self):
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67 locked = self.esema.acquire_lock(0)
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68 self.mutex.acquire_lock()
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69 if self._empty():
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70 # The queue is empyt -- we can't have esema
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71 self.mutex.release_lock()
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72 raise Empty
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73 if not locked:
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74 locked = self.esema.acquire_lock(0)
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75 if not locked:
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76 # Somebody else has esema
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77 # but we have mutex --
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78 # go out of their way
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79 self.mutex.release_lock()
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80 raise Empty
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81 was_full = self._full()
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82 item = self._get()
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83 if was_full:
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84 self.fsema.release_lock()
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85 if not self._empty():
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86 self.esema.release_lock()
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87 self.mutex.release_lock()
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88 return item
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89
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90 # XXX Need to define put_nowait() as well.
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91
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92
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93 # Override these methods to implement other queue organizations
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94 # (e.g. stack or priority queue).
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95 # These will only be called with appropriate locks held
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96
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97 # Initialize the queue representation
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98 def _init(self, maxsize):
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99 self.maxsize = maxsize
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100 self.queue = []
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101
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102 def _qsize(self):
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103 return len(self.queue)
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104
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105 # Check wheter the queue is empty
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106 def _empty(self):
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107 return not self.queue
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108
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109 # Check whether the queue is full
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110 def _full(self):
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111 return self.maxsize > 0 and len(self.queue) == self.maxsize
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112
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113 # Put a new item in the queue
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114 def _put(self, item):
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115 self.queue.append(item)
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116
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117 # Get an item from the queue
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118 def _get(self):
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119 item = self.queue[0]
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120 del self.queue[0]
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121 return item