1
# Copyright (C) 2005, 2006, 2007, 2008, 2009 Canonical Ltd
3
# This program is free software; you can redistribute it and/or modify
4
# it under the terms of the GNU General Public License as published by
5
# the Free Software Foundation; either version 2 of the License, or
6
# (at your option) any later version.
8
# This program is distributed in the hope that it will be useful,
9
# but WITHOUT ANY WARRANTY; without even the implied warranty of
10
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
11
# GNU General Public License for more details.
13
# You should have received a copy of the GNU General Public License
14
# along with this program; if not, write to the Free Software
15
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
18
"""Locking using OS file locks or file existence.
20
Note: This method of locking is generally deprecated in favour of LockDir, but
21
is used to lock local WorkingTrees, and by some old formats. It's accessed
22
through Transport.lock_read(), etc.
24
This module causes two methods, lock() and unlock() to be defined in
25
any way that works on the current platform.
27
It is not specified whether these locks are reentrant (i.e. can be
28
taken repeatedly by a single process) or whether they exclude
29
different threads in a single process. That reentrancy is provided by
32
This defines two classes: ReadLock and WriteLock, which can be
33
implemented in different ways on different platforms. Both have an
46
from bzrlib.hooks import HookPoint, Hooks
49
class LockHooks(Hooks):
53
self.create_hook(HookPoint('lock_acquired',
54
"Called with a bzrlib.lock.LockResult when a physical lock is "
55
"acquired.", (1, 8), None))
56
self.create_hook(HookPoint('lock_released',
57
"Called with a bzrlib.lock.LockResult when a physical lock is "
58
"released.", (1, 8), None))
59
self.create_hook(HookPoint('lock_broken',
60
"Called with a bzrlib.lock.LockResult when a physical lock is "
61
"broken.", (1, 15), None))
65
"""Base class for locks.
67
:cvar hooks: Hook dictionary for operations on locks.
73
class LockResult(object):
74
"""Result of an operation on a lock; passed to a hook"""
76
def __init__(self, lock_url, details=None):
77
"""Create a lock result for lock with optional details about the lock."""
78
self.lock_url = lock_url
79
self.details = details
81
def __eq__(self, other):
82
return self.lock_url == other.lock_url and self.details == other.details
85
return '%s(%s%s)' % (self.__class__.__name__,
86
self.lock_url, self.details)
96
have_ctypes_win32 = False
97
if sys.platform == 'win32':
100
import win32file, pywintypes, winerror
107
have_ctypes_win32 = True
112
class _OSLock(object):
118
def _open(self, filename, filemode):
119
self.filename = osutils.realpath(filename)
121
self.f = open(self.filename, filemode)
124
if e.errno in (errno.EACCES, errno.EPERM):
125
raise errors.LockFailed(self.filename, str(e))
126
if e.errno != errno.ENOENT:
129
# maybe this is an old branch (before may 2005)
130
trace.mutter("trying to create missing lock %r", self.filename)
132
self.f = open(self.filename, 'wb+')
136
"""Clear the self.f attribute cleanly."""
143
from warnings import warn
144
warn("lock on %r not released" % self.f)
148
raise NotImplementedError()
156
class _fcntl_FileLock(_OSLock):
159
fcntl.lockf(self.f, fcntl.LOCK_UN)
163
class _fcntl_WriteLock(_fcntl_FileLock):
167
def __init__(self, filename):
168
super(_fcntl_WriteLock, self).__init__()
169
# Check we can grab a lock before we actually open the file.
170
self.filename = osutils.realpath(filename)
171
if self.filename in _fcntl_WriteLock._open_locks:
173
raise errors.LockContention(self.filename)
175
self._open(self.filename, 'rb+')
176
# reserve a slot for this lock - even if the lockf call fails,
177
# at thisi point unlock() will be called, because self.f is set.
178
# TODO: make this fully threadsafe, if we decide we care.
179
_fcntl_WriteLock._open_locks.add(self.filename)
181
# LOCK_NB will cause IOError to be raised if we can't grab a
183
fcntl.lockf(self.f, fcntl.LOCK_EX | fcntl.LOCK_NB)
185
if e.errno in (errno.EAGAIN, errno.EACCES):
186
# We couldn't grab the lock
188
# we should be more precise about whats a locking
189
# error and whats a random-other error
190
raise errors.LockContention(self.filename, e)
193
_fcntl_WriteLock._open_locks.remove(self.filename)
197
class _fcntl_ReadLock(_fcntl_FileLock):
201
def __init__(self, filename):
202
super(_fcntl_ReadLock, self).__init__()
203
self.filename = osutils.realpath(filename)
204
_fcntl_ReadLock._open_locks.setdefault(self.filename, 0)
205
_fcntl_ReadLock._open_locks[self.filename] += 1
206
self._open(filename, 'rb')
208
# LOCK_NB will cause IOError to be raised if we can't grab a
210
fcntl.lockf(self.f, fcntl.LOCK_SH | fcntl.LOCK_NB)
212
# we should be more precise about whats a locking
213
# error and whats a random-other error
214
raise errors.LockContention(self.filename, e)
217
count = _fcntl_ReadLock._open_locks[self.filename]
219
del _fcntl_ReadLock._open_locks[self.filename]
221
_fcntl_ReadLock._open_locks[self.filename] = count - 1
224
def temporary_write_lock(self):
225
"""Try to grab a write lock on the file.
227
On platforms that support it, this will upgrade to a write lock
228
without unlocking the file.
229
Otherwise, this will release the read lock, and try to acquire a
232
:return: A token which can be used to switch back to a read lock.
234
if self.filename in _fcntl_WriteLock._open_locks:
235
raise AssertionError('file already locked: %r'
238
wlock = _fcntl_TemporaryWriteLock(self)
239
except errors.LockError:
240
# We didn't unlock, so we can just return 'self'
245
class _fcntl_TemporaryWriteLock(_OSLock):
246
"""A token used when grabbing a temporary_write_lock.
248
Call restore_read_lock() when you are done with the write lock.
251
def __init__(self, read_lock):
252
super(_fcntl_TemporaryWriteLock, self).__init__()
253
self._read_lock = read_lock
254
self.filename = read_lock.filename
256
count = _fcntl_ReadLock._open_locks[self.filename]
258
# Something else also has a read-lock, so we cannot grab a
260
raise errors.LockContention(self.filename)
262
if self.filename in _fcntl_WriteLock._open_locks:
263
raise AssertionError('file already locked: %r'
266
# See if we can open the file for writing. Another process might
267
# have a read lock. We don't use self._open() because we don't want
268
# to create the file if it exists. That would have already been
269
# done by _fcntl_ReadLock
271
new_f = open(self.filename, 'rb+')
273
if e.errno in (errno.EACCES, errno.EPERM):
274
raise errors.LockFailed(self.filename, str(e))
277
# LOCK_NB will cause IOError to be raised if we can't grab a
279
fcntl.lockf(new_f, fcntl.LOCK_EX | fcntl.LOCK_NB)
281
# TODO: Raise a more specific error based on the type of error
282
raise errors.LockContention(self.filename, e)
283
_fcntl_WriteLock._open_locks.add(self.filename)
287
def restore_read_lock(self):
288
"""Restore the original ReadLock."""
289
# For fcntl, since we never released the read lock, just release the
290
# write lock, and return the original lock.
291
fcntl.lockf(self.f, fcntl.LOCK_UN)
293
_fcntl_WriteLock._open_locks.remove(self.filename)
294
# Avoid reference cycles
295
read_lock = self._read_lock
296
self._read_lock = None
300
_lock_classes.append(('fcntl', _fcntl_WriteLock, _fcntl_ReadLock))
303
if have_pywin32 and sys.platform == 'win32':
304
if os.path.supports_unicode_filenames:
305
# for Windows NT/2K/XP/etc
306
win32file_CreateFile = win32file.CreateFileW
309
win32file_CreateFile = win32file.CreateFile
311
class _w32c_FileLock(_OSLock):
313
def _open(self, filename, access, share, cflags, pymode):
314
self.filename = osutils.realpath(filename)
316
self._handle = win32file_CreateFile(filename, access, share,
317
None, win32file.OPEN_ALWAYS,
318
win32file.FILE_ATTRIBUTE_NORMAL, None)
319
except pywintypes.error, e:
320
if e.args[0] == winerror.ERROR_ACCESS_DENIED:
321
raise errors.LockFailed(filename, e)
322
if e.args[0] == winerror.ERROR_SHARING_VIOLATION:
323
raise errors.LockContention(filename, e)
325
fd = win32file._open_osfhandle(self._handle, cflags)
326
self.f = os.fdopen(fd, pymode)
334
class _w32c_ReadLock(_w32c_FileLock):
335
def __init__(self, filename):
336
super(_w32c_ReadLock, self).__init__()
337
self._open(filename, win32file.GENERIC_READ,
338
win32file.FILE_SHARE_READ, os.O_RDONLY, "rb")
340
def temporary_write_lock(self):
341
"""Try to grab a write lock on the file.
343
On platforms that support it, this will upgrade to a write lock
344
without unlocking the file.
345
Otherwise, this will release the read lock, and try to acquire a
348
:return: A token which can be used to switch back to a read lock.
350
# I can't find a way to upgrade a read lock to a write lock without
351
# unlocking first. So here, we do just that.
354
wlock = _w32c_WriteLock(self.filename)
355
except errors.LockError:
356
return False, _w32c_ReadLock(self.filename)
360
class _w32c_WriteLock(_w32c_FileLock):
361
def __init__(self, filename):
362
super(_w32c_WriteLock, self).__init__()
364
win32file.GENERIC_READ | win32file.GENERIC_WRITE, 0,
367
def restore_read_lock(self):
368
"""Restore the original ReadLock."""
369
# For win32 we had to completely let go of the original lock, so we
370
# just unlock and create a new read lock.
372
return _w32c_ReadLock(self.filename)
375
_lock_classes.append(('pywin32', _w32c_WriteLock, _w32c_ReadLock))
378
if have_ctypes_win32:
379
from ctypes.wintypes import DWORD, LPCSTR, LPCWSTR
380
LPSECURITY_ATTRIBUTES = ctypes.c_void_p # used as NULL no need to declare
381
HANDLE = ctypes.c_int # rather than unsigned as in ctypes.wintypes
382
if os.path.supports_unicode_filenames:
383
_function_name = "CreateFileW"
386
_function_name = "CreateFileA"
387
class LPTSTR(LPCSTR):
388
def __new__(cls, obj):
389
return LPCSTR.__new__(cls, obj.encode("mbcs"))
391
# CreateFile <http://msdn.microsoft.com/en-us/library/aa363858.aspx>
392
_CreateFile = ctypes.WINFUNCTYPE(
393
HANDLE, # return value
395
DWORD, # dwDesiredAccess
397
LPSECURITY_ATTRIBUTES, # lpSecurityAttributes
398
DWORD, # dwCreationDisposition
399
DWORD, # dwFlagsAndAttributes
400
HANDLE # hTemplateFile
401
)((_function_name, ctypes.windll.kernel32))
403
INVALID_HANDLE_VALUE = -1
405
GENERIC_READ = 0x80000000
406
GENERIC_WRITE = 0x40000000
409
FILE_ATTRIBUTE_NORMAL = 128
411
ERROR_ACCESS_DENIED = 5
412
ERROR_SHARING_VIOLATION = 32
414
class _ctypes_FileLock(_OSLock):
416
def _open(self, filename, access, share, cflags, pymode):
417
self.filename = osutils.realpath(filename)
418
handle = _CreateFile(filename, access, share, None, OPEN_ALWAYS,
419
FILE_ATTRIBUTE_NORMAL, 0)
420
if handle in (INVALID_HANDLE_VALUE, 0):
421
e = ctypes.WinError()
422
if e.args[0] == ERROR_ACCESS_DENIED:
423
raise errors.LockFailed(filename, e)
424
if e.args[0] == ERROR_SHARING_VIOLATION:
425
raise errors.LockContention(filename, e)
427
fd = msvcrt.open_osfhandle(handle, cflags)
428
self.f = os.fdopen(fd, pymode)
435
class _ctypes_ReadLock(_ctypes_FileLock):
436
def __init__(self, filename):
437
super(_ctypes_ReadLock, self).__init__()
438
self._open(filename, GENERIC_READ, FILE_SHARE_READ, os.O_RDONLY,
441
def temporary_write_lock(self):
442
"""Try to grab a write lock on the file.
444
On platforms that support it, this will upgrade to a write lock
445
without unlocking the file.
446
Otherwise, this will release the read lock, and try to acquire a
449
:return: A token which can be used to switch back to a read lock.
451
# I can't find a way to upgrade a read lock to a write lock without
452
# unlocking first. So here, we do just that.
455
wlock = _ctypes_WriteLock(self.filename)
456
except errors.LockError:
457
return False, _ctypes_ReadLock(self.filename)
460
class _ctypes_WriteLock(_ctypes_FileLock):
461
def __init__(self, filename):
462
super(_ctypes_WriteLock, self).__init__()
463
self._open(filename, GENERIC_READ | GENERIC_WRITE, 0, os.O_RDWR,
466
def restore_read_lock(self):
467
"""Restore the original ReadLock."""
468
# For win32 we had to completely let go of the original lock, so we
469
# just unlock and create a new read lock.
471
return _ctypes_ReadLock(self.filename)
474
_lock_classes.append(('ctypes', _ctypes_WriteLock, _ctypes_ReadLock))
477
if len(_lock_classes) == 0:
478
raise NotImplementedError(
479
"We must have one of fcntl, pywin32, or ctypes available"
480
" to support OS locking."
484
# We default to using the first available lock class.
485
_lock_type, WriteLock, ReadLock = _lock_classes[0]