1
# Copyright (C) 2005-2010 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
17
"""Locking using OS file locks or file existence.
19
Note: This method of locking is generally deprecated in favour of LockDir, but
20
is used to lock local WorkingTrees, and by some old formats. It's accessed
21
through Transport.lock_read(), etc.
23
This module causes two methods, lock() and unlock() to be defined in
24
any way that works on the current platform.
26
It is not specified whether these locks are reentrant (i.e. can be
27
taken repeatedly by a single process) or whether they exclude
28
different threads in a single process. That reentrancy is provided by
31
This defines two classes: ReadLock and WriteLock, which can be
32
implemented in different ways on different platforms. Both have an
36
from __future__ import absolute_import
50
from bzrlib.hooks import Hooks
51
from bzrlib.i18n import gettext
53
class LockHooks(Hooks):
56
Hooks.__init__(self, "bzrlib.lock", "Lock.hooks")
57
self.add_hook('lock_acquired',
58
"Called with a bzrlib.lock.LockResult when a physical lock is "
60
self.add_hook('lock_released',
61
"Called with a bzrlib.lock.LockResult when a physical lock is "
63
self.add_hook('lock_broken',
64
"Called with a bzrlib.lock.LockResult when a physical lock is "
69
"""Base class for locks.
71
:cvar hooks: Hook dictionary for operations on locks.
77
class LockResult(object):
78
"""Result of an operation on a lock; passed to a hook"""
80
def __init__(self, lock_url, details=None):
81
"""Create a lock result for lock with optional details about the lock."""
82
self.lock_url = lock_url
83
self.details = details
85
def __eq__(self, other):
86
return self.lock_url == other.lock_url and self.details == other.details
89
return '%s(%s, %s)' % (self.__class__.__name__,
90
self.lock_url, self.details)
93
class LogicalLockResult(object):
94
"""The result of a lock_read/lock_write/lock_tree_write call on lockables.
96
:ivar unlock: A callable which will unlock the lock.
99
def __init__(self, unlock):
103
return "LogicalLockResult(%s)" % (self.unlock)
107
def cant_unlock_not_held(locked_object):
108
"""An attempt to unlock failed because the object was not locked.
110
This provides a policy point from which we can generate either a warning
113
# This is typically masking some other error and called from a finally
114
# block, so it's useful to have the option not to generate a new error
115
# here. You can use -Werror to make it fatal. It should possibly also
117
if 'unlock' in debug.debug_flags:
118
warnings.warn("%r is already unlocked" % (locked_object,),
121
raise errors.LockNotHeld(locked_object)
131
have_ctypes_win32 = False
132
if sys.platform == 'win32':
135
import win32file, pywintypes, winerror
142
have_ctypes_win32 = True
147
class _OSLock(object):
153
def _open(self, filename, filemode):
154
self.filename = osutils.realpath(filename)
156
self.f = open(self.filename, filemode)
159
if e.errno in (errno.EACCES, errno.EPERM):
160
raise errors.LockFailed(self.filename, str(e))
161
if e.errno != errno.ENOENT:
164
# maybe this is an old branch (before may 2005)
165
trace.mutter("trying to create missing lock %r", self.filename)
167
self.f = open(self.filename, 'wb+')
171
"""Clear the self.f attribute cleanly."""
177
raise NotImplementedError()
185
class _fcntl_FileLock(_OSLock):
188
fcntl.lockf(self.f, fcntl.LOCK_UN)
192
class _fcntl_WriteLock(_fcntl_FileLock):
196
def __init__(self, filename):
197
super(_fcntl_WriteLock, self).__init__()
198
# Check we can grab a lock before we actually open the file.
199
self.filename = osutils.realpath(filename)
200
if self.filename in _fcntl_WriteLock._open_locks:
202
raise errors.LockContention(self.filename)
203
if self.filename in _fcntl_ReadLock._open_locks:
204
if 'strict_locks' in debug.debug_flags:
206
raise errors.LockContention(self.filename)
208
trace.mutter('Write lock taken w/ an open read lock on: %s'
211
self._open(self.filename, 'rb+')
212
# reserve a slot for this lock - even if the lockf call fails,
213
# at this point unlock() will be called, because self.f is set.
214
# TODO: make this fully threadsafe, if we decide we care.
215
_fcntl_WriteLock._open_locks.add(self.filename)
217
# LOCK_NB will cause IOError to be raised if we can't grab a
219
fcntl.lockf(self.f, fcntl.LOCK_EX | fcntl.LOCK_NB)
221
if e.errno in (errno.EAGAIN, errno.EACCES):
222
# We couldn't grab the lock
224
# we should be more precise about whats a locking
225
# error and whats a random-other error
226
raise errors.LockContention(self.filename, e)
229
_fcntl_WriteLock._open_locks.remove(self.filename)
233
class _fcntl_ReadLock(_fcntl_FileLock):
237
def __init__(self, filename):
238
super(_fcntl_ReadLock, self).__init__()
239
self.filename = osutils.realpath(filename)
240
if self.filename in _fcntl_WriteLock._open_locks:
241
if 'strict_locks' in debug.debug_flags:
242
# We raise before calling _open so we don't need to
244
raise errors.LockContention(self.filename)
246
trace.mutter('Read lock taken w/ an open write lock on: %s'
248
_fcntl_ReadLock._open_locks.setdefault(self.filename, 0)
249
_fcntl_ReadLock._open_locks[self.filename] += 1
250
self._open(filename, 'rb')
252
# LOCK_NB will cause IOError to be raised if we can't grab a
254
fcntl.lockf(self.f, fcntl.LOCK_SH | fcntl.LOCK_NB)
256
# we should be more precise about whats a locking
257
# error and whats a random-other error
258
raise errors.LockContention(self.filename, e)
261
count = _fcntl_ReadLock._open_locks[self.filename]
263
del _fcntl_ReadLock._open_locks[self.filename]
265
_fcntl_ReadLock._open_locks[self.filename] = count - 1
268
def temporary_write_lock(self):
269
"""Try to grab a write lock on the file.
271
On platforms that support it, this will upgrade to a write lock
272
without unlocking the file.
273
Otherwise, this will release the read lock, and try to acquire a
276
:return: A token which can be used to switch back to a read lock.
278
if self.filename in _fcntl_WriteLock._open_locks:
279
raise AssertionError('file already locked: %r'
282
wlock = _fcntl_TemporaryWriteLock(self)
283
except errors.LockError:
284
# We didn't unlock, so we can just return 'self'
289
class _fcntl_TemporaryWriteLock(_OSLock):
290
"""A token used when grabbing a temporary_write_lock.
292
Call restore_read_lock() when you are done with the write lock.
295
def __init__(self, read_lock):
296
super(_fcntl_TemporaryWriteLock, self).__init__()
297
self._read_lock = read_lock
298
self.filename = read_lock.filename
300
count = _fcntl_ReadLock._open_locks[self.filename]
302
# Something else also has a read-lock, so we cannot grab a
304
raise errors.LockContention(self.filename)
306
if self.filename in _fcntl_WriteLock._open_locks:
307
raise AssertionError('file already locked: %r'
310
# See if we can open the file for writing. Another process might
311
# have a read lock. We don't use self._open() because we don't want
312
# to create the file if it exists. That would have already been
313
# done by _fcntl_ReadLock
315
new_f = open(self.filename, 'rb+')
317
if e.errno in (errno.EACCES, errno.EPERM):
318
raise errors.LockFailed(self.filename, str(e))
321
# LOCK_NB will cause IOError to be raised if we can't grab a
323
fcntl.lockf(new_f, fcntl.LOCK_EX | fcntl.LOCK_NB)
325
# TODO: Raise a more specific error based on the type of error
326
raise errors.LockContention(self.filename, e)
327
_fcntl_WriteLock._open_locks.add(self.filename)
331
def restore_read_lock(self):
332
"""Restore the original ReadLock."""
333
# For fcntl, since we never released the read lock, just release the
334
# write lock, and return the original lock.
335
fcntl.lockf(self.f, fcntl.LOCK_UN)
337
_fcntl_WriteLock._open_locks.remove(self.filename)
338
# Avoid reference cycles
339
read_lock = self._read_lock
340
self._read_lock = None
344
_lock_classes.append(('fcntl', _fcntl_WriteLock, _fcntl_ReadLock))
347
if have_pywin32 and sys.platform == 'win32':
348
if os.path.supports_unicode_filenames:
349
# for Windows NT/2K/XP/etc
350
win32file_CreateFile = win32file.CreateFileW
353
win32file_CreateFile = win32file.CreateFile
355
class _w32c_FileLock(_OSLock):
357
def _open(self, filename, access, share, cflags, pymode):
358
self.filename = osutils.realpath(filename)
360
self._handle = win32file_CreateFile(filename, access, share,
361
None, win32file.OPEN_ALWAYS,
362
win32file.FILE_ATTRIBUTE_NORMAL, None)
363
except pywintypes.error, e:
364
if e.args[0] == winerror.ERROR_ACCESS_DENIED:
365
raise errors.LockFailed(filename, e)
366
if e.args[0] == winerror.ERROR_SHARING_VIOLATION:
367
raise errors.LockContention(filename, e)
369
fd = win32file._open_osfhandle(self._handle, cflags)
370
self.f = os.fdopen(fd, pymode)
378
class _w32c_ReadLock(_w32c_FileLock):
379
def __init__(self, filename):
380
super(_w32c_ReadLock, self).__init__()
381
self._open(filename, win32file.GENERIC_READ,
382
win32file.FILE_SHARE_READ, os.O_RDONLY, "rb")
384
def temporary_write_lock(self):
385
"""Try to grab a write lock on the file.
387
On platforms that support it, this will upgrade to a write lock
388
without unlocking the file.
389
Otherwise, this will release the read lock, and try to acquire a
392
:return: A token which can be used to switch back to a read lock.
394
# I can't find a way to upgrade a read lock to a write lock without
395
# unlocking first. So here, we do just that.
398
wlock = _w32c_WriteLock(self.filename)
399
except errors.LockError:
400
return False, _w32c_ReadLock(self.filename)
404
class _w32c_WriteLock(_w32c_FileLock):
405
def __init__(self, filename):
406
super(_w32c_WriteLock, self).__init__()
408
win32file.GENERIC_READ | win32file.GENERIC_WRITE, 0,
411
def restore_read_lock(self):
412
"""Restore the original ReadLock."""
413
# For win32 we had to completely let go of the original lock, so we
414
# just unlock and create a new read lock.
416
return _w32c_ReadLock(self.filename)
419
_lock_classes.append(('pywin32', _w32c_WriteLock, _w32c_ReadLock))
422
if have_ctypes_win32:
423
from ctypes.wintypes import DWORD, LPCSTR, LPCWSTR
424
LPSECURITY_ATTRIBUTES = ctypes.c_void_p # used as NULL no need to declare
425
HANDLE = ctypes.c_int # rather than unsigned as in ctypes.wintypes
426
if os.path.supports_unicode_filenames:
427
_function_name = "CreateFileW"
430
_function_name = "CreateFileA"
431
class LPTSTR(LPCSTR):
432
def __new__(cls, obj):
433
return LPCSTR.__new__(cls, obj.encode("mbcs"))
435
# CreateFile <http://msdn.microsoft.com/en-us/library/aa363858.aspx>
436
_CreateFile = ctypes.WINFUNCTYPE(
437
HANDLE, # return value
439
DWORD, # dwDesiredAccess
441
LPSECURITY_ATTRIBUTES, # lpSecurityAttributes
442
DWORD, # dwCreationDisposition
443
DWORD, # dwFlagsAndAttributes
444
HANDLE # hTemplateFile
445
)((_function_name, ctypes.windll.kernel32))
447
INVALID_HANDLE_VALUE = -1
449
GENERIC_READ = 0x80000000
450
GENERIC_WRITE = 0x40000000
453
FILE_ATTRIBUTE_NORMAL = 128
455
ERROR_ACCESS_DENIED = 5
456
ERROR_SHARING_VIOLATION = 32
458
class _ctypes_FileLock(_OSLock):
460
def _open(self, filename, access, share, cflags, pymode):
461
self.filename = osutils.realpath(filename)
462
handle = _CreateFile(filename, access, share, None, OPEN_ALWAYS,
463
FILE_ATTRIBUTE_NORMAL, 0)
464
if handle in (INVALID_HANDLE_VALUE, 0):
465
e = ctypes.WinError()
466
if e.args[0] == ERROR_ACCESS_DENIED:
467
raise errors.LockFailed(filename, e)
468
if e.args[0] == ERROR_SHARING_VIOLATION:
469
raise errors.LockContention(filename, e)
471
fd = msvcrt.open_osfhandle(handle, cflags)
472
self.f = os.fdopen(fd, pymode)
479
class _ctypes_ReadLock(_ctypes_FileLock):
480
def __init__(self, filename):
481
super(_ctypes_ReadLock, self).__init__()
482
self._open(filename, GENERIC_READ, FILE_SHARE_READ, os.O_RDONLY,
485
def temporary_write_lock(self):
486
"""Try to grab a write lock on the file.
488
On platforms that support it, this will upgrade to a write lock
489
without unlocking the file.
490
Otherwise, this will release the read lock, and try to acquire a
493
:return: A token which can be used to switch back to a read lock.
495
# I can't find a way to upgrade a read lock to a write lock without
496
# unlocking first. So here, we do just that.
499
wlock = _ctypes_WriteLock(self.filename)
500
except errors.LockError:
501
return False, _ctypes_ReadLock(self.filename)
504
class _ctypes_WriteLock(_ctypes_FileLock):
505
def __init__(self, filename):
506
super(_ctypes_WriteLock, self).__init__()
507
self._open(filename, GENERIC_READ | GENERIC_WRITE, 0, os.O_RDWR,
510
def restore_read_lock(self):
511
"""Restore the original ReadLock."""
512
# For win32 we had to completely let go of the original lock, so we
513
# just unlock and create a new read lock.
515
return _ctypes_ReadLock(self.filename)
518
_lock_classes.append(('ctypes', _ctypes_WriteLock, _ctypes_ReadLock))
521
if len(_lock_classes) == 0:
522
raise NotImplementedError(
523
"We must have one of fcntl, pywin32, or ctypes available"
524
" to support OS locking."
528
# We default to using the first available lock class.
529
_lock_type, WriteLock, ReadLock = _lock_classes[0]
532
class _RelockDebugMixin(object):
533
"""Mixin support for -Drelock flag.
535
Add this as a base class then call self._note_lock with 'r' or 'w' when
536
acquiring a read- or write-lock. If this object was previously locked (and
537
locked the same way), and -Drelock is set, then this will trace.note a
543
def _note_lock(self, lock_type):
544
if 'relock' in debug.debug_flags and self._prev_lock == lock_type:
549
trace.note(gettext('{0!r} was {1} locked again'), self, type_name)
550
self._prev_lock = lock_type
552
@contextlib.contextmanager
553
def write_locked(lockable):
554
lockable.lock_write()
added
removed
bzrlib/lock.py
