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33
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1 """
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2 lockfile.py - Platform-independent advisory file locks.
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3
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4 Requires Python 2.5 unless you apply 2.4.diff
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5 Locking is done on a per-thread basis instead of a per-process basis.
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6
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7 Usage:
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8
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9 >>> lock = LockFile('somefile')
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10 >>> try:
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11 ... lock.acquire()
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12 ... except AlreadyLocked:
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13 ... print 'somefile', 'is locked already.'
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14 ... except LockFailed:
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15 ... print 'somefile', 'can\\'t be locked.'
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16 ... else:
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17 ... print 'got lock'
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18 got lock
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19 >>> print lock.is_locked()
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20 True
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21 >>> lock.release()
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22
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23 >>> lock = LockFile('somefile')
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24 >>> print lock.is_locked()
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25 False
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26 >>> with lock:
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27 ... print lock.is_locked()
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28 True
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29 >>> print lock.is_locked()
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30 False
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31
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32 >>> lock = LockFile('somefile')
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33 >>> # It is okay to lock twice from the same thread...
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34 >>> with lock:
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35 ... lock.acquire()
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36 ...
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37 >>> # Though no counter is kept, so you can't unlock multiple times...
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38 >>> print lock.is_locked()
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39 False
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40
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41 Exceptions:
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42
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43 Error - base class for other exceptions
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44 LockError - base class for all locking exceptions
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45 AlreadyLocked - Another thread or process already holds the lock
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46 LockFailed - Lock failed for some other reason
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47 UnlockError - base class for all unlocking exceptions
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48 AlreadyUnlocked - File was not locked.
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49 NotMyLock - File was locked but not by the current thread/process
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50 """
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51
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52 from __future__ import absolute_import
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53
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54 import sys
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55 import socket
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56 import os
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57 import threading
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58 import time
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59 import urllib
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60 import warnings
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61 import functools
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62
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63 # Work with PEP8 and non-PEP8 versions of threading module.
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64 if not hasattr(threading, "current_thread"):
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65 threading.current_thread = threading.currentThread
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66 if not hasattr(threading.Thread, "get_name"):
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67 threading.Thread.get_name = threading.Thread.getName
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68
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69 __all__ = ['Error', 'LockError', 'LockTimeout', 'AlreadyLocked',
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70 'LockFailed', 'UnlockError', 'NotLocked', 'NotMyLock',
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71 'LinkLockFile', 'MkdirLockFile', 'SQLiteLockFile',
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72 'LockBase', 'locked']
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73
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74 class Error(Exception):
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75 """
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76 Base class for other exceptions.
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77
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78 >>> try:
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79 ... raise Error
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80 ... except Exception:
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81 ... pass
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82 """
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83 pass
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84
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85 class LockError(Error):
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86 """
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87 Base class for error arising from attempts to acquire the lock.
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88
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89 >>> try:
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90 ... raise LockError
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91 ... except Error:
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92 ... pass
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93 """
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94 pass
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95
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96 class LockTimeout(LockError):
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97 """Raised when lock creation fails within a user-defined period of time.
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98
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99 >>> try:
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100 ... raise LockTimeout
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101 ... except LockError:
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102 ... pass
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103 """
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104 pass
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105
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106 class AlreadyLocked(LockError):
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107 """Some other thread/process is locking the file.
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108
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109 >>> try:
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110 ... raise AlreadyLocked
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111 ... except LockError:
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112 ... pass
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113 """
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114 pass
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115
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116 class LockFailed(LockError):
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117 """Lock file creation failed for some other reason.
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118
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119 >>> try:
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120 ... raise LockFailed
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121 ... except LockError:
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122 ... pass
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123 """
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124 pass
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125
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126 class UnlockError(Error):
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127 """
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128 Base class for errors arising from attempts to release the lock.
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129
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130 >>> try:
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131 ... raise UnlockError
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132 ... except Error:
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133 ... pass
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134 """
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135 pass
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136
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137 class NotLocked(UnlockError):
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138 """Raised when an attempt is made to unlock an unlocked file.
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139
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140 >>> try:
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141 ... raise NotLocked
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142 ... except UnlockError:
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143 ... pass
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144 """
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145 pass
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146
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147 class NotMyLock(UnlockError):
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148 """Raised when an attempt is made to unlock a file someone else locked.
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149
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150 >>> try:
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151 ... raise NotMyLock
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152 ... except UnlockError:
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153 ... pass
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154 """
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155 pass
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156
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157 class LockBase:
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158 """Base class for platform-specific lock classes."""
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159 def __init__(self, path, threaded=True, timeout=None):
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160 """
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161 >>> lock = LockBase('somefile')
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162 >>> lock = LockBase('somefile', threaded=False)
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163 """
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164 self.path = path
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165 self.lock_file = os.path.abspath(path) + ".lock"
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166 self.hostname = socket.gethostname()
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167 self.pid = os.getpid()
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168 if threaded:
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169 t = threading.current_thread()
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170 # Thread objects in Python 2.4 and earlier do not have ident
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171 # attrs. Worm around that.
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172 ident = getattr(t, "ident", hash(t))
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173 self.tname = "-%x" % (ident & 0xffffffff)
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174 else:
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175 self.tname = ""
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176 dirname = os.path.dirname(self.lock_file)
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177
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178 # unique name is mostly about the current process, but must
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179 # also contain the path -- otherwise, two adjacent locked
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180 # files conflict (one file gets locked, creating lock-file and
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181 # unique file, the other one gets locked, creating lock-file
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182 # and overwriting the already existing lock-file, then one
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183 # gets unlocked, deleting both lock-file and unique file,
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184 # finally the last lock errors out upon releasing.
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185 self.unique_name = os.path.join(dirname,
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186 "%s%s.%s%s" % (self.hostname,
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187 self.tname,
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188 self.pid,
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189 hash(self.path)))
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190 self.timeout = timeout
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191
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192 def acquire(self, timeout=None):
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193 """
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194 Acquire the lock.
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195
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196 * If timeout is omitted (or None), wait forever trying to lock the
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197 file.
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198
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199 * If timeout > 0, try to acquire the lock for that many seconds. If
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200 the lock period expires and the file is still locked, raise
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201 LockTimeout.
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202
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203 * If timeout <= 0, raise AlreadyLocked immediately if the file is
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204 already locked.
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205 """
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206 raise NotImplemented("implement in subclass")
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207
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208 def release(self):
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209 """
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210 Release the lock.
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211
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212 If the file is not locked, raise NotLocked.
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213 """
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214 raise NotImplemented("implement in subclass")
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215
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216 def is_locked(self):
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217 """
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218 Tell whether or not the file is locked.
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219 """
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220 raise NotImplemented("implement in subclass")
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221
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222 def i_am_locking(self):
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223 """
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224 Return True if this object is locking the file.
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225 """
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226 raise NotImplemented("implement in subclass")
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227
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228 def break_lock(self):
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229 """
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230 Remove a lock. Useful if a locking thread failed to unlock.
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231 """
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232 raise NotImplemented("implement in subclass")
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233
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234 def __enter__(self):
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235 """
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236 Context manager support.
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237 """
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238 self.acquire()
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239 return self
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240
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241 def __exit__(self, *_exc):
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242 """
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243 Context manager support.
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244 """
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245 self.release()
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246
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247 def __repr__(self):
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248 return "<%s: %r -- %r>" % (self.__class__.__name__, self.unique_name,
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249 self.path)
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250
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251 def _fl_helper(cls, mod, *args, **kwds):
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252 warnings.warn("Import from %s module instead of lockfile package" % mod,
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253 DeprecationWarning, stacklevel=2)
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254 # This is a bit funky, but it's only for awhile. The way the unit tests
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255 # are constructed this function winds up as an unbound method, so it
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256 # actually takes three args, not two. We want to toss out self.
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257 if not isinstance(args[0], str):
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258 # We are testing, avoid the first arg
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259 args = args[1:]
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260 if len(args) == 1 and not kwds:
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261 kwds["threaded"] = True
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262 return cls(*args, **kwds)
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263
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264 def LinkFileLock(*args, **kwds):
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265 """Factory function provided for backwards compatibility.
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266
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267 Do not use in new code. Instead, import LinkLockFile from the
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268 lockfile.linklockfile module.
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269 """
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270 from . import linklockfile
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271 return _fl_helper(linklockfile.LinkLockFile, "lockfile.linklockfile",
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272 *args, **kwds)
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273
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274 def MkdirFileLock(*args, **kwds):
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275 """Factory function provided for backwards compatibility.
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276
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277 Do not use in new code. Instead, import MkdirLockFile from the
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278 lockfile.mkdirlockfile module.
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279 """
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280 from . import mkdirlockfile
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281 return _fl_helper(mkdirlockfile.MkdirLockFile, "lockfile.mkdirlockfile",
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282 *args, **kwds)
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283
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284 def SQLiteFileLock(*args, **kwds):
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285 """Factory function provided for backwards compatibility.
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286
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287 Do not use in new code. Instead, import SQLiteLockFile from the
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288 lockfile.mkdirlockfile module.
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289 """
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290 from . import sqlitelockfile
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291 return _fl_helper(sqlitelockfile.SQLiteLockFile, "lockfile.sqlitelockfile",
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292 *args, **kwds)
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293
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294 def locked(path, timeout=None):
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295 """Decorator which enables locks for decorated function.
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296
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297 Arguments:
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298 - path: path for lockfile.
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299 - timeout (optional): Timeout for acquiring lock.
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300
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301 Usage:
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302 @locked('/var/run/myname', timeout=0)
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303 def myname(...):
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304 ...
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305 """
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306 def decor(func):
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307 @functools.wraps(func)
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308 def wrapper(*args, **kwargs):
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309 lock = FileLock(path, timeout=timeout)
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310 lock.acquire()
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311 try:
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312 return func(*args, **kwargs)
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313 finally:
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314 lock.release()
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315 return wrapper
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316 return decor
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317
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318 if hasattr(os, "link"):
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319 from . import linklockfile as _llf
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320 LockFile = _llf.LinkLockFile
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321 else:
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322 from . import mkdirlockfile as _mlf
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323 LockFile = _mlf.MkdirLockFile
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324
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325 FileLock = LockFile
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326
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