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comparison env/lib/python3.7/site-packages/filelock.py @ 0:26e78fe6e8c4 draft

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"planemo upload commit c699937486c35866861690329de38ec1a5d9f783"
author shellac
date Sat, 02 May 2020 07:14:21 -0400
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1 # This is free and unencumbered software released into the public domain.
2 #
3 # Anyone is free to copy, modify, publish, use, compile, sell, or
4 # distribute this software, either in source code form or as a compiled
5 # binary, for any purpose, commercial or non-commercial, and by any
6 # means.
7 #
8 # In jurisdictions that recognize copyright laws, the author or authors
9 # of this software dedicate any and all copyright interest in the
10 # software to the public domain. We make this dedication for the benefit
11 # of the public at large and to the detriment of our heirs and
12 # successors. We intend this dedication to be an overt act of
13 # relinquishment in perpetuity of all present and future rights to this
14 # software under copyright law.
15 #
16 # THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
17 # EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
18 # MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
19 # IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
20 # OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
21 # ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
22 # OTHER DEALINGS IN THE SOFTWARE.
23 #
24 # For more information, please refer to <http://unlicense.org>
25
26 """
27 A platform independent file lock that supports the with-statement.
28 """
29
30
31 # Modules
32 # ------------------------------------------------
33 import logging
34 import os
35 import threading
36 import time
37 try:
38 import warnings
39 except ImportError:
40 warnings = None
41
42 try:
43 import msvcrt
44 except ImportError:
45 msvcrt = None
46
47 try:
48 import fcntl
49 except ImportError:
50 fcntl = None
51
52
53 # Backward compatibility
54 # ------------------------------------------------
55 try:
56 TimeoutError
57 except NameError:
58 TimeoutError = OSError
59
60
61 # Data
62 # ------------------------------------------------
63 __all__ = [
64 "Timeout",
65 "BaseFileLock",
66 "WindowsFileLock",
67 "UnixFileLock",
68 "SoftFileLock",
69 "FileLock"
70 ]
71
72 __version__ = "3.0.12"
73
74
75 _logger = None
76 def logger():
77 """Returns the logger instance used in this module."""
78 global _logger
79 _logger = _logger or logging.getLogger(__name__)
80 return _logger
81
82
83 # Exceptions
84 # ------------------------------------------------
85 class Timeout(TimeoutError):
86 """
87 Raised when the lock could not be acquired in *timeout*
88 seconds.
89 """
90
91 def __init__(self, lock_file):
92 """
93 """
94 #: The path of the file lock.
95 self.lock_file = lock_file
96 return None
97
98 def __str__(self):
99 temp = "The file lock '{}' could not be acquired."\
100 .format(self.lock_file)
101 return temp
102
103
104 # Classes
105 # ------------------------------------------------
106
107 # This is a helper class which is returned by :meth:`BaseFileLock.acquire`
108 # and wraps the lock to make sure __enter__ is not called twice when entering
109 # the with statement.
110 # If we would simply return *self*, the lock would be acquired again
111 # in the *__enter__* method of the BaseFileLock, but not released again
112 # automatically.
113 #
114 # :seealso: issue #37 (memory leak)
115 class _Acquire_ReturnProxy(object):
116
117 def __init__(self, lock):
118 self.lock = lock
119 return None
120
121 def __enter__(self):
122 return self.lock
123
124 def __exit__(self, exc_type, exc_value, traceback):
125 self.lock.release()
126 return None
127
128
129 class BaseFileLock(object):
130 """
131 Implements the base class of a file lock.
132 """
133
134 def __init__(self, lock_file, timeout = -1):
135 """
136 """
137 # The path to the lock file.
138 self._lock_file = lock_file
139
140 # The file descriptor for the *_lock_file* as it is returned by the
141 # os.open() function.
142 # This file lock is only NOT None, if the object currently holds the
143 # lock.
144 self._lock_file_fd = None
145
146 # The default timeout value.
147 self.timeout = timeout
148
149 # We use this lock primarily for the lock counter.
150 self._thread_lock = threading.Lock()
151
152 # The lock counter is used for implementing the nested locking
153 # mechanism. Whenever the lock is acquired, the counter is increased and
154 # the lock is only released, when this value is 0 again.
155 self._lock_counter = 0
156 return None
157
158 @property
159 def lock_file(self):
160 """
161 The path to the lock file.
162 """
163 return self._lock_file
164
165 @property
166 def timeout(self):
167 """
168 You can set a default timeout for the filelock. It will be used as
169 fallback value in the acquire method, if no timeout value (*None*) is
170 given.
171
172 If you want to disable the timeout, set it to a negative value.
173
174 A timeout of 0 means, that there is exactly one attempt to acquire the
175 file lock.
176
177 .. versionadded:: 2.0.0
178 """
179 return self._timeout
180
181 @timeout.setter
182 def timeout(self, value):
183 """
184 """
185 self._timeout = float(value)
186 return None
187
188 # Platform dependent locking
189 # --------------------------------------------
190
191 def _acquire(self):
192 """
193 Platform dependent. If the file lock could be
194 acquired, self._lock_file_fd holds the file descriptor
195 of the lock file.
196 """
197 raise NotImplementedError()
198
199 def _release(self):
200 """
201 Releases the lock and sets self._lock_file_fd to None.
202 """
203 raise NotImplementedError()
204
205 # Platform independent methods
206 # --------------------------------------------
207
208 @property
209 def is_locked(self):
210 """
211 True, if the object holds the file lock.
212
213 .. versionchanged:: 2.0.0
214
215 This was previously a method and is now a property.
216 """
217 return self._lock_file_fd is not None
218
219 def acquire(self, timeout=None, poll_intervall=0.05):
220 """
221 Acquires the file lock or fails with a :exc:`Timeout` error.
222
223 .. code-block:: python
224
225 # You can use this method in the context manager (recommended)
226 with lock.acquire():
227 pass
228
229 # Or use an equivalent try-finally construct:
230 lock.acquire()
231 try:
232 pass
233 finally:
234 lock.release()
235
236 :arg float timeout:
237 The maximum time waited for the file lock.
238 If ``timeout < 0``, there is no timeout and this method will
239 block until the lock could be acquired.
240 If ``timeout`` is None, the default :attr:`~timeout` is used.
241
242 :arg float poll_intervall:
243 We check once in *poll_intervall* seconds if we can acquire the
244 file lock.
245
246 :raises Timeout:
247 if the lock could not be acquired in *timeout* seconds.
248
249 .. versionchanged:: 2.0.0
250
251 This method returns now a *proxy* object instead of *self*,
252 so that it can be used in a with statement without side effects.
253 """
254 # Use the default timeout, if no timeout is provided.
255 if timeout is None:
256 timeout = self.timeout
257
258 # Increment the number right at the beginning.
259 # We can still undo it, if something fails.
260 with self._thread_lock:
261 self._lock_counter += 1
262
263 lock_id = id(self)
264 lock_filename = self._lock_file
265 start_time = time.time()
266 try:
267 while True:
268 with self._thread_lock:
269 if not self.is_locked:
270 logger().debug('Attempting to acquire lock %s on %s', lock_id, lock_filename)
271 self._acquire()
272
273 if self.is_locked:
274 logger().info('Lock %s acquired on %s', lock_id, lock_filename)
275 break
276 elif timeout >= 0 and time.time() - start_time > timeout:
277 logger().debug('Timeout on acquiring lock %s on %s', lock_id, lock_filename)
278 raise Timeout(self._lock_file)
279 else:
280 logger().debug(
281 'Lock %s not acquired on %s, waiting %s seconds ...',
282 lock_id, lock_filename, poll_intervall
283 )
284 time.sleep(poll_intervall)
285 except:
286 # Something did go wrong, so decrement the counter.
287 with self._thread_lock:
288 self._lock_counter = max(0, self._lock_counter - 1)
289
290 raise
291 return _Acquire_ReturnProxy(lock = self)
292
293 def release(self, force = False):
294 """
295 Releases the file lock.
296
297 Please note, that the lock is only completly released, if the lock
298 counter is 0.
299
300 Also note, that the lock file itself is not automatically deleted.
301
302 :arg bool force:
303 If true, the lock counter is ignored and the lock is released in
304 every case.
305 """
306 with self._thread_lock:
307
308 if self.is_locked:
309 self._lock_counter -= 1
310
311 if self._lock_counter == 0 or force:
312 lock_id = id(self)
313 lock_filename = self._lock_file
314
315 logger().debug('Attempting to release lock %s on %s', lock_id, lock_filename)
316 self._release()
317 self._lock_counter = 0
318 logger().info('Lock %s released on %s', lock_id, lock_filename)
319
320 return None
321
322 def __enter__(self):
323 self.acquire()
324 return self
325
326 def __exit__(self, exc_type, exc_value, traceback):
327 self.release()
328 return None
329
330 def __del__(self):
331 self.release(force = True)
332 return None
333
334
335 # Windows locking mechanism
336 # ~~~~~~~~~~~~~~~~~~~~~~~~~
337
338 class WindowsFileLock(BaseFileLock):
339 """
340 Uses the :func:`msvcrt.locking` function to hard lock the lock file on
341 windows systems.
342 """
343
344 def _acquire(self):
345 open_mode = os.O_RDWR | os.O_CREAT | os.O_TRUNC
346
347 try:
348 fd = os.open(self._lock_file, open_mode)
349 except OSError:
350 pass
351 else:
352 try:
353 msvcrt.locking(fd, msvcrt.LK_NBLCK, 1)
354 except (IOError, OSError):
355 os.close(fd)
356 else:
357 self._lock_file_fd = fd
358 return None
359
360 def _release(self):
361 fd = self._lock_file_fd
362 self._lock_file_fd = None
363 msvcrt.locking(fd, msvcrt.LK_UNLCK, 1)
364 os.close(fd)
365
366 try:
367 os.remove(self._lock_file)
368 # Probably another instance of the application
369 # that acquired the file lock.
370 except OSError:
371 pass
372 return None
373
374 # Unix locking mechanism
375 # ~~~~~~~~~~~~~~~~~~~~~~
376
377 class UnixFileLock(BaseFileLock):
378 """
379 Uses the :func:`fcntl.flock` to hard lock the lock file on unix systems.
380 """
381
382 def _acquire(self):
383 open_mode = os.O_RDWR | os.O_CREAT | os.O_TRUNC
384 fd = os.open(self._lock_file, open_mode)
385
386 try:
387 fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
388 except (IOError, OSError):
389 os.close(fd)
390 else:
391 self._lock_file_fd = fd
392 return None
393
394 def _release(self):
395 # Do not remove the lockfile:
396 #
397 # https://github.com/benediktschmitt/py-filelock/issues/31
398 # https://stackoverflow.com/questions/17708885/flock-removing-locked-file-without-race-condition
399 fd = self._lock_file_fd
400 self._lock_file_fd = None
401 fcntl.flock(fd, fcntl.LOCK_UN)
402 os.close(fd)
403 return None
404
405 # Soft lock
406 # ~~~~~~~~~
407
408 class SoftFileLock(BaseFileLock):
409 """
410 Simply watches the existence of the lock file.
411 """
412
413 def _acquire(self):
414 open_mode = os.O_WRONLY | os.O_CREAT | os.O_EXCL | os.O_TRUNC
415 try:
416 fd = os.open(self._lock_file, open_mode)
417 except (IOError, OSError):
418 pass
419 else:
420 self._lock_file_fd = fd
421 return None
422
423 def _release(self):
424 os.close(self._lock_file_fd)
425 self._lock_file_fd = None
426
427 try:
428 os.remove(self._lock_file)
429 # The file is already deleted and that's what we want.
430 except OSError:
431 pass
432 return None
433
434
435 # Platform filelock
436 # ~~~~~~~~~~~~~~~~~
437
438 #: Alias for the lock, which should be used for the current platform. On
439 #: Windows, this is an alias for :class:`WindowsFileLock`, on Unix for
440 #: :class:`UnixFileLock` and otherwise for :class:`SoftFileLock`.
441 FileLock = None
442
443 if msvcrt:
444 FileLock = WindowsFileLock
445 elif fcntl:
446 FileLock = UnixFileLock
447 else:
448 FileLock = SoftFileLock
449
450 if warnings is not None:
451 warnings.warn("only soft file lock is available")