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1 | 162c1c1f | Guido Trotter | #
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2 | 162c1c1f | Guido Trotter | #
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3 | 162c1c1f | Guido Trotter | |
4 | 162c1c1f | Guido Trotter | # Copyright (C) 2006, 2007 Google Inc.
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5 | 162c1c1f | Guido Trotter | #
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6 | 162c1c1f | Guido Trotter | # This program is free software; you can redistribute it and/or modify
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7 | 162c1c1f | Guido Trotter | # it under the terms of the GNU General Public License as published by
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8 | 162c1c1f | Guido Trotter | # the Free Software Foundation; either version 2 of the License, or
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9 | 162c1c1f | Guido Trotter | # (at your option) any later version.
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10 | 162c1c1f | Guido Trotter | #
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11 | 162c1c1f | Guido Trotter | # This program is distributed in the hope that it will be useful, but
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12 | 162c1c1f | Guido Trotter | # WITHOUT ANY WARRANTY; without even the implied warranty of
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13 | 162c1c1f | Guido Trotter | # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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14 | 162c1c1f | Guido Trotter | # General Public License for more details.
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15 | 162c1c1f | Guido Trotter | #
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16 | 162c1c1f | Guido Trotter | # You should have received a copy of the GNU General Public License
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17 | 162c1c1f | Guido Trotter | # along with this program; if not, write to the Free Software
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18 | 162c1c1f | Guido Trotter | # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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19 | 162c1c1f | Guido Trotter | # 02110-1301, USA.
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20 | 162c1c1f | Guido Trotter | |
21 | 162c1c1f | Guido Trotter | """Module implementing the Ganeti locking code."""
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22 | 162c1c1f | Guido Trotter | |
23 | 162c1c1f | Guido Trotter | # pylint: disable-msg=W0613,W0201
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24 | 162c1c1f | Guido Trotter | |
25 | 162c1c1f | Guido Trotter | import threading |
26 | a95fd5d7 | Guido Trotter | # Wouldn't it be better to define LockingError in the locking module?
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27 | a95fd5d7 | Guido Trotter | # Well, for now that's how the rest of the code does it...
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28 | a95fd5d7 | Guido Trotter | from ganeti import errors |
29 | 162c1c1f | Guido Trotter | |
30 | 162c1c1f | Guido Trotter | |
31 | 162c1c1f | Guido Trotter | class SharedLock: |
32 | 162c1c1f | Guido Trotter | """Implements a shared lock.
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33 | 162c1c1f | Guido Trotter |
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34 | 162c1c1f | Guido Trotter | Multiple threads can acquire the lock in a shared way, calling
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35 | 162c1c1f | Guido Trotter | acquire_shared(). In order to acquire the lock in an exclusive way threads
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36 | 162c1c1f | Guido Trotter | can call acquire_exclusive().
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37 | 162c1c1f | Guido Trotter |
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38 | 162c1c1f | Guido Trotter | The lock prevents starvation but does not guarantee that threads will acquire
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39 | 162c1c1f | Guido Trotter | the shared lock in the order they queued for it, just that they will
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40 | 162c1c1f | Guido Trotter | eventually do so.
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41 | 162c1c1f | Guido Trotter |
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42 | 162c1c1f | Guido Trotter | """
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43 | 162c1c1f | Guido Trotter | def __init__(self): |
44 | d6646186 | Guido Trotter | """Construct a new SharedLock"""
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45 | 162c1c1f | Guido Trotter | # we have two conditions, c_shr and c_exc, sharing the same lock.
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46 | 162c1c1f | Guido Trotter | self.__lock = threading.Lock()
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47 | 162c1c1f | Guido Trotter | self.__turn_shr = threading.Condition(self.__lock) |
48 | 162c1c1f | Guido Trotter | self.__turn_exc = threading.Condition(self.__lock) |
49 | 162c1c1f | Guido Trotter | |
50 | 162c1c1f | Guido Trotter | # current lock holders
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51 | 162c1c1f | Guido Trotter | self.__shr = set() |
52 | 162c1c1f | Guido Trotter | self.__exc = None |
53 | 162c1c1f | Guido Trotter | |
54 | 162c1c1f | Guido Trotter | # lock waiters
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55 | 162c1c1f | Guido Trotter | self.__nwait_exc = 0 |
56 | 162c1c1f | Guido Trotter | self.__nwait_shr = 0 |
57 | 162c1c1f | Guido Trotter | |
58 | a95fd5d7 | Guido Trotter | # is this lock in the deleted state?
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59 | a95fd5d7 | Guido Trotter | self.__deleted = False |
60 | a95fd5d7 | Guido Trotter | |
61 | 162c1c1f | Guido Trotter | def __is_sharer(self): |
62 | 162c1c1f | Guido Trotter | """Is the current thread sharing the lock at this time?"""
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63 | 162c1c1f | Guido Trotter | return threading.currentThread() in self.__shr |
64 | 162c1c1f | Guido Trotter | |
65 | 162c1c1f | Guido Trotter | def __is_exclusive(self): |
66 | 162c1c1f | Guido Trotter | """Is the current thread holding the lock exclusively at this time?"""
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67 | 162c1c1f | Guido Trotter | return threading.currentThread() == self.__exc |
68 | 162c1c1f | Guido Trotter | |
69 | 162c1c1f | Guido Trotter | def __is_owned(self, shared=-1): |
70 | 162c1c1f | Guido Trotter | """Is the current thread somehow owning the lock at this time?
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71 | 162c1c1f | Guido Trotter |
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72 | 162c1c1f | Guido Trotter | This is a private version of the function, which presumes you're holding
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73 | 162c1c1f | Guido Trotter | the internal lock.
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74 | 162c1c1f | Guido Trotter |
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75 | 162c1c1f | Guido Trotter | """
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76 | 162c1c1f | Guido Trotter | if shared < 0: |
77 | 162c1c1f | Guido Trotter | return self.__is_sharer() or self.__is_exclusive() |
78 | 162c1c1f | Guido Trotter | elif shared:
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79 | 162c1c1f | Guido Trotter | return self.__is_sharer() |
80 | 162c1c1f | Guido Trotter | else:
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81 | 162c1c1f | Guido Trotter | return self.__is_exclusive() |
82 | 162c1c1f | Guido Trotter | |
83 | 162c1c1f | Guido Trotter | def _is_owned(self, shared=-1): |
84 | 162c1c1f | Guido Trotter | """Is the current thread somehow owning the lock at this time?
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85 | 162c1c1f | Guido Trotter |
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86 | 162c1c1f | Guido Trotter | Args:
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87 | 162c1c1f | Guido Trotter | shared:
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88 | 162c1c1f | Guido Trotter | < 0: check for any type of ownership (default)
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89 | 162c1c1f | Guido Trotter | 0: check for exclusive ownership
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90 | 162c1c1f | Guido Trotter | > 0: check for shared ownership
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91 | 162c1c1f | Guido Trotter |
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92 | 162c1c1f | Guido Trotter | """
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93 | 162c1c1f | Guido Trotter | self.__lock.acquire()
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94 | 162c1c1f | Guido Trotter | try:
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95 | 162c1c1f | Guido Trotter | result = self.__is_owned(shared)
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96 | 162c1c1f | Guido Trotter | finally:
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97 | 162c1c1f | Guido Trotter | self.__lock.release()
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98 | 162c1c1f | Guido Trotter | |
99 | 162c1c1f | Guido Trotter | return result
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100 | 162c1c1f | Guido Trotter | |
101 | a95fd5d7 | Guido Trotter | def __wait(self,c): |
102 | a95fd5d7 | Guido Trotter | """Wait on the given condition, and raise an exception if the current lock
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103 | a95fd5d7 | Guido Trotter | is declared deleted in the meantime.
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104 | a95fd5d7 | Guido Trotter |
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105 | a95fd5d7 | Guido Trotter | Args:
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106 | a95fd5d7 | Guido Trotter | c: condition to wait on
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107 | a95fd5d7 | Guido Trotter |
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108 | a95fd5d7 | Guido Trotter | """
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109 | a95fd5d7 | Guido Trotter | c.wait() |
110 | a95fd5d7 | Guido Trotter | if self.__deleted: |
111 | a95fd5d7 | Guido Trotter | raise errors.LockError('deleted lock') |
112 | a95fd5d7 | Guido Trotter | |
113 | a95fd5d7 | Guido Trotter | def __exclusive_acquire(self): |
114 | a95fd5d7 | Guido Trotter | """Acquire the lock exclusively.
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115 | a95fd5d7 | Guido Trotter |
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116 | a95fd5d7 | Guido Trotter | This is a private function that presumes you are already holding the
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117 | a95fd5d7 | Guido Trotter | internal lock. It's defined separately to avoid code duplication between
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118 | a95fd5d7 | Guido Trotter | acquire() and delete()
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119 | a95fd5d7 | Guido Trotter |
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120 | a95fd5d7 | Guido Trotter | """
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121 | a95fd5d7 | Guido Trotter | self.__nwait_exc += 1 |
122 | a95fd5d7 | Guido Trotter | try:
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123 | a95fd5d7 | Guido Trotter | # This is to save ourselves from a nasty race condition that could
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124 | a95fd5d7 | Guido Trotter | # theoretically make the sharers starve.
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125 | a95fd5d7 | Guido Trotter | if self.__nwait_shr > 0 or self.__nwait_exc > 1: |
126 | a95fd5d7 | Guido Trotter | self.__wait(self.__turn_exc) |
127 | a95fd5d7 | Guido Trotter | |
128 | a95fd5d7 | Guido Trotter | while len(self.__shr) > 0 or self.__exc is not None: |
129 | a95fd5d7 | Guido Trotter | self.__wait(self.__turn_exc) |
130 | a95fd5d7 | Guido Trotter | |
131 | a95fd5d7 | Guido Trotter | self.__exc = threading.currentThread()
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132 | a95fd5d7 | Guido Trotter | finally:
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133 | a95fd5d7 | Guido Trotter | self.__nwait_exc -= 1 |
134 | a95fd5d7 | Guido Trotter | |
135 | a95fd5d7 | Guido Trotter | |
136 | 162c1c1f | Guido Trotter | def acquire(self, blocking=1, shared=0): |
137 | 162c1c1f | Guido Trotter | """Acquire a shared lock.
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138 | 162c1c1f | Guido Trotter |
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139 | 162c1c1f | Guido Trotter | Args:
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140 | 162c1c1f | Guido Trotter | shared: whether to acquire in shared mode. By default an exclusive lock
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141 | 162c1c1f | Guido Trotter | will be acquired.
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142 | 162c1c1f | Guido Trotter | blocking: whether to block while trying to acquire or to operate in try-lock mode.
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143 | 162c1c1f | Guido Trotter | this locking mode is not supported yet.
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144 | 162c1c1f | Guido Trotter |
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145 | 162c1c1f | Guido Trotter | """
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146 | 162c1c1f | Guido Trotter | if not blocking: |
147 | 162c1c1f | Guido Trotter | # We don't have non-blocking mode for now
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148 | 162c1c1f | Guido Trotter | raise NotImplementedError |
149 | 162c1c1f | Guido Trotter | |
150 | 162c1c1f | Guido Trotter | self.__lock.acquire()
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151 | 162c1c1f | Guido Trotter | try:
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152 | a95fd5d7 | Guido Trotter | if self.__deleted: |
153 | a95fd5d7 | Guido Trotter | raise errors.LockError('deleted lock') |
154 | a95fd5d7 | Guido Trotter | |
155 | 162c1c1f | Guido Trotter | # We cannot acquire the lock if we already have it
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156 | 162c1c1f | Guido Trotter | assert not self.__is_owned(), "double acquire() on a non-recursive lock" |
157 | 162c1c1f | Guido Trotter | |
158 | 162c1c1f | Guido Trotter | if shared:
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159 | 162c1c1f | Guido Trotter | self.__nwait_shr += 1 |
160 | 162c1c1f | Guido Trotter | try:
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161 | 162c1c1f | Guido Trotter | # If there is an exclusive holder waiting we have to wait. We'll
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162 | 162c1c1f | Guido Trotter | # only do this once, though, when we start waiting for the lock. Then
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163 | 162c1c1f | Guido Trotter | # we'll just wait while there are no exclusive holders.
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164 | 162c1c1f | Guido Trotter | if self.__nwait_exc > 0: |
165 | 162c1c1f | Guido Trotter | # TODO: if !blocking...
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166 | a95fd5d7 | Guido Trotter | self.__wait(self.__turn_shr) |
167 | 162c1c1f | Guido Trotter | |
168 | 162c1c1f | Guido Trotter | while self.__exc is not None: |
169 | 162c1c1f | Guido Trotter | # TODO: if !blocking...
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170 | a95fd5d7 | Guido Trotter | self.__wait(self.__turn_shr) |
171 | 162c1c1f | Guido Trotter | |
172 | 162c1c1f | Guido Trotter | self.__shr.add(threading.currentThread())
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173 | 162c1c1f | Guido Trotter | finally:
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174 | 162c1c1f | Guido Trotter | self.__nwait_shr -= 1 |
175 | 162c1c1f | Guido Trotter | |
176 | 162c1c1f | Guido Trotter | else:
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177 | a95fd5d7 | Guido Trotter | # TODO: if !blocking...
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178 | a95fd5d7 | Guido Trotter | # (or modify __exclusive_acquire for non-blocking mode)
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179 | a95fd5d7 | Guido Trotter | self.__exclusive_acquire()
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180 | 162c1c1f | Guido Trotter | |
181 | 162c1c1f | Guido Trotter | finally:
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182 | 162c1c1f | Guido Trotter | self.__lock.release()
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183 | 162c1c1f | Guido Trotter | |
184 | 162c1c1f | Guido Trotter | return True |
185 | 162c1c1f | Guido Trotter | |
186 | 162c1c1f | Guido Trotter | def release(self): |
187 | 162c1c1f | Guido Trotter | """Release a Shared Lock.
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188 | 162c1c1f | Guido Trotter |
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189 | 162c1c1f | Guido Trotter | You must have acquired the lock, either in shared or in exclusive mode,
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190 | 162c1c1f | Guido Trotter | before calling this function.
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191 | 162c1c1f | Guido Trotter |
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192 | 162c1c1f | Guido Trotter | """
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193 | 162c1c1f | Guido Trotter | self.__lock.acquire()
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194 | 162c1c1f | Guido Trotter | try:
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195 | 162c1c1f | Guido Trotter | # Autodetect release type
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196 | 162c1c1f | Guido Trotter | if self.__is_exclusive(): |
197 | 162c1c1f | Guido Trotter | self.__exc = None |
198 | 162c1c1f | Guido Trotter | |
199 | 162c1c1f | Guido Trotter | # An exclusive holder has just had the lock, time to put it in shared
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200 | 162c1c1f | Guido Trotter | # mode if there are shared holders waiting. Otherwise wake up the next
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201 | 162c1c1f | Guido Trotter | # exclusive holder.
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202 | 162c1c1f | Guido Trotter | if self.__nwait_shr > 0: |
203 | 162c1c1f | Guido Trotter | self.__turn_shr.notifyAll()
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204 | 162c1c1f | Guido Trotter | elif self.__nwait_exc > 0: |
205 | 162c1c1f | Guido Trotter | self.__turn_exc.notify()
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206 | 162c1c1f | Guido Trotter | |
207 | 162c1c1f | Guido Trotter | elif self.__is_sharer(): |
208 | 162c1c1f | Guido Trotter | self.__shr.remove(threading.currentThread())
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209 | 162c1c1f | Guido Trotter | |
210 | 162c1c1f | Guido Trotter | # If there are shared holders waiting there *must* be an exclusive holder
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211 | 162c1c1f | Guido Trotter | # waiting as well; otherwise what were they waiting for?
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212 | 162c1c1f | Guido Trotter | assert (self.__nwait_shr == 0 or self.__nwait_exc > 0, |
213 | 162c1c1f | Guido Trotter | "Lock sharers waiting while no exclusive is queueing")
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214 | 162c1c1f | Guido Trotter | |
215 | 162c1c1f | Guido Trotter | # If there are no more shared holders and some exclusive holders are
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216 | 162c1c1f | Guido Trotter | # waiting let's wake one up.
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217 | 162c1c1f | Guido Trotter | if len(self.__shr) == 0 and self.__nwait_exc > 0: |
218 | 162c1c1f | Guido Trotter | self.__turn_exc.notify()
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219 | 162c1c1f | Guido Trotter | |
220 | 162c1c1f | Guido Trotter | else:
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221 | 162c1c1f | Guido Trotter | assert False, "Cannot release non-owned lock" |
222 | 162c1c1f | Guido Trotter | |
223 | 162c1c1f | Guido Trotter | finally:
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224 | 162c1c1f | Guido Trotter | self.__lock.release()
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225 | 162c1c1f | Guido Trotter | |
226 | a95fd5d7 | Guido Trotter | def delete(self, blocking=1): |
227 | a95fd5d7 | Guido Trotter | """Delete a Shared Lock.
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228 | a95fd5d7 | Guido Trotter |
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229 | a95fd5d7 | Guido Trotter | This operation will declare the lock for removal. First the lock will be
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230 | a95fd5d7 | Guido Trotter | acquired in exclusive mode if you don't already own it, then the lock
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231 | a95fd5d7 | Guido Trotter | will be put in a state where any future and pending acquire() fail.
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232 | a95fd5d7 | Guido Trotter |
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233 | a95fd5d7 | Guido Trotter | Args:
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234 | a95fd5d7 | Guido Trotter | blocking: whether to block while trying to acquire or to operate in
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235 | a95fd5d7 | Guido Trotter | try-lock mode. this locking mode is not supported yet unless
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236 | a95fd5d7 | Guido Trotter | you are already holding exclusively the lock.
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237 | a95fd5d7 | Guido Trotter |
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238 | a95fd5d7 | Guido Trotter | """
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239 | a95fd5d7 | Guido Trotter | self.__lock.acquire()
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240 | a95fd5d7 | Guido Trotter | try:
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241 | a95fd5d7 | Guido Trotter | assert not self.__is_sharer(), "cannot delete() a lock while sharing it" |
242 | a95fd5d7 | Guido Trotter | |
243 | a95fd5d7 | Guido Trotter | if self.__deleted: |
244 | a95fd5d7 | Guido Trotter | raise errors.LockError('deleted lock') |
245 | a95fd5d7 | Guido Trotter | |
246 | a95fd5d7 | Guido Trotter | if not self.__is_exclusive(): |
247 | a95fd5d7 | Guido Trotter | if not blocking: |
248 | a95fd5d7 | Guido Trotter | # We don't have non-blocking mode for now
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249 | a95fd5d7 | Guido Trotter | raise NotImplementedError |
250 | a95fd5d7 | Guido Trotter | self.__exclusive_acquire()
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251 | a95fd5d7 | Guido Trotter | |
252 | a95fd5d7 | Guido Trotter | self.__deleted = True |
253 | a95fd5d7 | Guido Trotter | self.__exc = None |
254 | a95fd5d7 | Guido Trotter | # Wake up everybody, they will fail acquiring the lock and
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255 | a95fd5d7 | Guido Trotter | # raise an exception instead.
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256 | a95fd5d7 | Guido Trotter | self.__turn_exc.notifyAll()
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257 | a95fd5d7 | Guido Trotter | self.__turn_shr.notifyAll()
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258 | a95fd5d7 | Guido Trotter | |
259 | a95fd5d7 | Guido Trotter | finally:
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260 | a95fd5d7 | Guido Trotter | self.__lock.release()
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