~bzr-pqm/bzr/bzr.dev

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
# Copyright (C) 2005, 2006, 2007, 2008, 2009 Canonical Ltd
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA


"""Locking using OS file locks or file existence.

Note: This method of locking is generally deprecated in favour of LockDir, but
is used to lock local WorkingTrees, and by some old formats.  It's accessed
through Transport.lock_read(), etc.

This module causes two methods, lock() and unlock() to be defined in
any way that works on the current platform.

It is not specified whether these locks are reentrant (i.e. can be
taken repeatedly by a single process) or whether they exclude
different threads in a single process.  That reentrancy is provided by
LockableFiles.

This defines two classes: ReadLock and WriteLock, which can be
implemented in different ways on different platforms.  Both have an
unlock() method.
"""

import errno
import sys

from bzrlib import (
    errors,
    osutils,
    trace,
    )
from bzrlib.hooks import HookPoint, Hooks


class LockHooks(Hooks):

    def __init__(self):
        Hooks.__init__(self)
        self.create_hook(HookPoint('lock_acquired',
            "Called with a bzrlib.lock.LockResult when a physical lock is "
            "acquired.", (1, 8), None))
        self.create_hook(HookPoint('lock_released',
            "Called with a bzrlib.lock.LockResult when a physical lock is "
            "released.", (1, 8), None))
        self.create_hook(HookPoint('lock_broken',
            "Called with a bzrlib.lock.LockResult when a physical lock is "
            "broken.", (1, 15), None))


class Lock(object):
    """Base class for locks.

    :cvar hooks: Hook dictionary for operations on locks.
    """

    hooks = LockHooks()


class LockResult(object):
    """Result of an operation on a lock; passed to a hook"""

    def __init__(self, lock_url, details=None):
        """Create a lock result for lock with optional details about the lock."""
        self.lock_url = lock_url
        self.details = details

    def __eq__(self, other):
        return self.lock_url == other.lock_url and self.details == other.details

    def __repr__(self):
        return '%s(%s%s)' % (self.__class__.__name__,
                             self.lock_url, self.details)


try:
    import fcntl
    have_fcntl = True
except ImportError:
    have_fcntl = False

have_pywin32 = False
have_ctypes_win32 = False
if sys.platform == 'win32':
    import msvcrt
    try:
        import win32con, win32file, pywintypes, winerror
        have_pywin32 = True
    except ImportError:
        pass

    try:
        import ctypes
        have_ctypes_win32 = True
    except ImportError:
        pass


class _OSLock(object):

    def __init__(self):
        self.f = None
        self.filename = None

    def _open(self, filename, filemode):
        self.filename = osutils.realpath(filename)
        try:
            self.f = open(self.filename, filemode)
            return self.f
        except IOError, e:
            if e.errno in (errno.EACCES, errno.EPERM):
                raise errors.LockFailed(self.filename, str(e))
            if e.errno != errno.ENOENT:
                raise

            # maybe this is an old branch (before may 2005)
            trace.mutter("trying to create missing lock %r", self.filename)

            self.f = open(self.filename, 'wb+')
            return self.f

    def _clear_f(self):
        """Clear the self.f attribute cleanly."""
        if self.f:
            self.f.close()
            self.f = None

    def __del__(self):
        if self.f:
            from warnings import warn
            warn("lock on %r not released" % self.f)
            self.unlock()

    def unlock(self):
        raise NotImplementedError()


_lock_classes = []


if have_fcntl:
    LOCK_SH = fcntl.LOCK_SH
    LOCK_NB = fcntl.LOCK_NB
    lock_EX = fcntl.LOCK_EX


    class _fcntl_FileLock(_OSLock):

        def _unlock(self):
            fcntl.lockf(self.f, fcntl.LOCK_UN)
            self._clear_f()


    class _fcntl_WriteLock(_fcntl_FileLock):

        _open_locks = set()

        def __init__(self, filename):
            super(_fcntl_WriteLock, self).__init__()
            # Check we can grab a lock before we actually open the file.
            self.filename = osutils.realpath(filename)
            if self.filename in _fcntl_WriteLock._open_locks:
                self._clear_f()
                raise errors.LockContention(self.filename)

            self._open(self.filename, 'rb+')
            # reserve a slot for this lock - even if the lockf call fails,
            # at thisi point unlock() will be called, because self.f is set.
            # TODO: make this fully threadsafe, if we decide we care.
            _fcntl_WriteLock._open_locks.add(self.filename)
            try:
                # LOCK_NB will cause IOError to be raised if we can't grab a
                # lock right away.
                fcntl.lockf(self.f, fcntl.LOCK_EX | fcntl.LOCK_NB)
            except IOError, e:
                if e.errno in (errno.EAGAIN, errno.EACCES):
                    # We couldn't grab the lock
                    self.unlock()
                # we should be more precise about whats a locking
                # error and whats a random-other error
                raise errors.LockContention(self.filename, e)

        def unlock(self):
            _fcntl_WriteLock._open_locks.remove(self.filename)
            self._unlock()


    class _fcntl_ReadLock(_fcntl_FileLock):

        _open_locks = {}

        def __init__(self, filename):
            super(_fcntl_ReadLock, self).__init__()
            self.filename = osutils.realpath(filename)
            _fcntl_ReadLock._open_locks.setdefault(self.filename, 0)
            _fcntl_ReadLock._open_locks[self.filename] += 1
            self._open(filename, 'rb')
            try:
                # LOCK_NB will cause IOError to be raised if we can't grab a
                # lock right away.
                fcntl.lockf(self.f, fcntl.LOCK_SH | fcntl.LOCK_NB)
            except IOError, e:
                # we should be more precise about whats a locking
                # error and whats a random-other error
                raise errors.LockContention(self.filename, e)

        def unlock(self):
            count = _fcntl_ReadLock._open_locks[self.filename]
            if count == 1:
                del _fcntl_ReadLock._open_locks[self.filename]
            else:
                _fcntl_ReadLock._open_locks[self.filename] = count - 1
            self._unlock()

        def temporary_write_lock(self):
            """Try to grab a write lock on the file.

            On platforms that support it, this will upgrade to a write lock
            without unlocking the file.
            Otherwise, this will release the read lock, and try to acquire a
            write lock.

            :return: A token which can be used to switch back to a read lock.
            """
            if self.filename in _fcntl_WriteLock._open_locks:
                raise AssertionError('file already locked: %r'
                    % (self.filename,))
            try:
                wlock = _fcntl_TemporaryWriteLock(self)
            except errors.LockError:
                # We didn't unlock, so we can just return 'self'
                return False, self
            return True, wlock


    class _fcntl_TemporaryWriteLock(_OSLock):
        """A token used when grabbing a temporary_write_lock.

        Call restore_read_lock() when you are done with the write lock.
        """

        def __init__(self, read_lock):
            super(_fcntl_TemporaryWriteLock, self).__init__()
            self._read_lock = read_lock
            self.filename = read_lock.filename

            count = _fcntl_ReadLock._open_locks[self.filename]
            if count > 1:
                # Something else also has a read-lock, so we cannot grab a
                # write lock.
                raise errors.LockContention(self.filename)

            if self.filename in _fcntl_WriteLock._open_locks:
                raise AssertionError('file already locked: %r'
                    % (self.filename,))

            # See if we can open the file for writing. Another process might
            # have a read lock. We don't use self._open() because we don't want
            # to create the file if it exists. That would have already been
            # done by _fcntl_ReadLock
            try:
                new_f = open(self.filename, 'rb+')
            except IOError, e:
                if e.errno in (errno.EACCES, errno.EPERM):
                    raise errors.LockFailed(self.filename, str(e))
                raise
            try:
                # LOCK_NB will cause IOError to be raised if we can't grab a
                # lock right away.
                fcntl.lockf(new_f, fcntl.LOCK_EX | fcntl.LOCK_NB)
            except IOError, e:
                # TODO: Raise a more specific error based on the type of error
                raise errors.LockContention(self.filename, e)
            _fcntl_WriteLock._open_locks.add(self.filename)

            self.f = new_f

        def restore_read_lock(self):
            """Restore the original ReadLock."""
            # For fcntl, since we never released the read lock, just release the
            # write lock, and return the original lock.
            fcntl.lockf(self.f, fcntl.LOCK_UN)
            self._clear_f()
            _fcntl_WriteLock._open_locks.remove(self.filename)
            # Avoid reference cycles
            read_lock = self._read_lock
            self._read_lock = None
            return read_lock


    _lock_classes.append(('fcntl', _fcntl_WriteLock, _fcntl_ReadLock))


if have_pywin32 and sys.platform == 'win32':
    LOCK_SH = 0 # the default
    LOCK_EX = win32con.LOCKFILE_EXCLUSIVE_LOCK
    LOCK_NB = win32con.LOCKFILE_FAIL_IMMEDIATELY


    class _w32c_FileLock(_OSLock):

        def _lock(self, filename, openmode, lockmode):
            self._open(filename, openmode)

            self.hfile = msvcrt.get_osfhandle(self.f.fileno())
            overlapped = pywintypes.OVERLAPPED()
            try:
                win32file.LockFileEx(self.hfile, lockmode, 0, 0x7fff0000,
                                     overlapped)
            except pywintypes.error, e:
                self._clear_f()
                if e.args[0] in (winerror.ERROR_LOCK_VIOLATION,):
                    raise errors.LockContention(filename)
                ## import pdb; pdb.set_trace()
                raise
            except Exception, e:
                self._clear_f()
                raise errors.LockContention(filename, e)

        def unlock(self):
            overlapped = pywintypes.OVERLAPPED()
            try:
                win32file.UnlockFileEx(self.hfile, 0, 0x7fff0000, overlapped)
                self._clear_f()
            except Exception, e:
                raise errors.LockContention(self.filename, e)


    class _w32c_ReadLock(_w32c_FileLock):
        def __init__(self, filename):
            super(_w32c_ReadLock, self).__init__()
            self._lock(filename, 'rb', LOCK_SH + LOCK_NB)

        def temporary_write_lock(self):
            """Try to grab a write lock on the file.

            On platforms that support it, this will upgrade to a write lock
            without unlocking the file.
            Otherwise, this will release the read lock, and try to acquire a
            write lock.

            :return: A token which can be used to switch back to a read lock.
            """
            # I can't find a way to upgrade a read lock to a write lock without
            # unlocking first. So here, we do just that.
            self.unlock()
            try:
                wlock = _w32c_WriteLock(self.filename)
            except errors.LockError:
                return False, _w32c_ReadLock(self.filename)
            return True, wlock


    class _w32c_WriteLock(_w32c_FileLock):
        def __init__(self, filename):
            super(_w32c_WriteLock, self).__init__()
            self._lock(filename, 'rb+', LOCK_EX + LOCK_NB)

        def restore_read_lock(self):
            """Restore the original ReadLock."""
            # For win32 we had to completely let go of the original lock, so we
            # just unlock and create a new read lock.
            self.unlock()
            return _w32c_ReadLock(self.filename)


    _lock_classes.append(('pywin32', _w32c_WriteLock, _w32c_ReadLock))


if have_ctypes_win32:
    # These constants were copied from the win32con.py module.
    LOCKFILE_FAIL_IMMEDIATELY = 1
    LOCKFILE_EXCLUSIVE_LOCK = 2
    # Constant taken from winerror.py module
    ERROR_LOCK_VIOLATION = 33

    LOCK_SH = 0
    LOCK_EX = LOCKFILE_EXCLUSIVE_LOCK
    LOCK_NB = LOCKFILE_FAIL_IMMEDIATELY
    _LockFileEx = ctypes.windll.kernel32.LockFileEx
    _UnlockFileEx = ctypes.windll.kernel32.UnlockFileEx

    ### Define the OVERLAPPED structure.
    #   http://msdn2.microsoft.com/en-us/library/ms684342.aspx
    # typedef struct _OVERLAPPED {
    #   ULONG_PTR Internal;
    #   ULONG_PTR InternalHigh;
    #   union {
    #     struct {
    #       DWORD Offset;
    #       DWORD OffsetHigh;
    #     };
    #     PVOID Pointer;
    #   };
    #   HANDLE hEvent;
    # } OVERLAPPED,

    class _inner_struct(ctypes.Structure):
        _fields_ = [('Offset', ctypes.c_uint), # DWORD
                    ('OffsetHigh', ctypes.c_uint), # DWORD
                   ]

    class _inner_union(ctypes.Union):
        _fields_  = [('anon_struct', _inner_struct), # struct
                     ('Pointer', ctypes.c_void_p), # PVOID
                    ]

    class OVERLAPPED(ctypes.Structure):
        _fields_ = [('Internal', ctypes.c_void_p), # ULONG_PTR
                    ('InternalHigh', ctypes.c_void_p), # ULONG_PTR
                    ('_inner_union', _inner_union),
                    ('hEvent', ctypes.c_void_p), # HANDLE
                   ]

    class _ctypes_FileLock(_OSLock):

        def _lock(self, filename, openmode, lockmode):
            self._open(filename, openmode)

            self.hfile = msvcrt.get_osfhandle(self.f.fileno())
            overlapped = OVERLAPPED()
            result = _LockFileEx(self.hfile, # HANDLE hFile
                                 lockmode,   # DWORD dwFlags
                                 0,          # DWORD dwReserved
                                 0x7fffffff, # DWORD nNumberOfBytesToLockLow
                                 0x00000000, # DWORD nNumberOfBytesToLockHigh
                                 ctypes.byref(overlapped), # lpOverlapped
                                )
            if result == 0:
                last_err = ctypes.GetLastError()
                self._clear_f()
                if last_err in (ERROR_LOCK_VIOLATION,):
                    raise errors.LockContention(filename)
                raise errors.LockContention(filename,
                    'Unknown locking error: %s' % (last_err,))

        def unlock(self):
            overlapped = OVERLAPPED()
            result = _UnlockFileEx(self.hfile, # HANDLE hFile
                                   0,          # DWORD dwReserved
                                   0x7fffffff, # DWORD nNumberOfBytesToLockLow
                                   0x00000000, # DWORD nNumberOfBytesToLockHigh
                                   ctypes.byref(overlapped), # lpOverlapped
                                  )
            if result == 0:
                last_err = ctypes.GetLastError()
                self._clear_f()
                raise errors.LockContention(self.filename,
                    'Unknown unlocking error: %s' % (last_err,))
            self._clear_f()


    class _ctypes_ReadLock(_ctypes_FileLock):
        def __init__(self, filename):
            super(_ctypes_ReadLock, self).__init__()
            self._lock(filename, 'rb', LOCK_SH + LOCK_NB)

        def temporary_write_lock(self):
            """Try to grab a write lock on the file.

            On platforms that support it, this will upgrade to a write lock
            without unlocking the file.
            Otherwise, this will release the read lock, and try to acquire a
            write lock.

            :return: A token which can be used to switch back to a read lock.
            """
            # I can't find a way to upgrade a read lock to a write lock without
            # unlocking first. So here, we do just that.
            self.unlock()
            try:
                wlock = _ctypes_WriteLock(self.filename)
            except errors.LockError:
                return False, _ctypes_ReadLock(self.filename)
            return True, wlock

    class _ctypes_WriteLock(_ctypes_FileLock):
        def __init__(self, filename):
            super(_ctypes_WriteLock, self).__init__()
            self._lock(filename, 'rb+', LOCK_EX + LOCK_NB)

        def restore_read_lock(self):
            """Restore the original ReadLock."""
            # For win32 we had to completely let go of the original lock, so we
            # just unlock and create a new read lock.
            self.unlock()
            return _ctypes_ReadLock(self.filename)


    _lock_classes.append(('ctypes', _ctypes_WriteLock, _ctypes_ReadLock))


if len(_lock_classes) == 0:
    raise NotImplementedError(
        "We must have one of fcntl, pywin32, or ctypes available"
        " to support OS locking."
        )


# We default to using the first available lock class.
_lock_type, WriteLock, ReadLock = _lock_classes[0]