88
88
>>> t = MemoryTransport()
89
89
>>> l = LockDir(t, 'sample-lock')
91
>>> token = l.wait_lock()
92
92
>>> # do something here
95
Some classes of stale locks can be predicted by checking: the host name is the
96
same as the local host name; the user name is the same as the local user; the
97
process id no longer exists. The check on user name is not strictly necessary
98
but helps protect against colliding host names.
102
# TODO: We sometimes have the problem that our attempt to rename '1234' to
103
# 'held' fails because the transport server moves into an existing directory,
104
# rather than failing the rename. If we made the info file name the same as
105
# the locked directory name we would avoid this problem because moving into
106
# the held directory would implicitly clash. However this would not mesh with
107
# the existing locking code and needs a new format of the containing object.
108
# -- robertc, mbp 20070628
99
from warnings import warn
100
from StringIO import StringIO
123
from bzrlib.decorators import only_raises
124
103
from bzrlib.errors import (
125
104
DirectoryNotEmpty,
127
106
LockBreakMismatch,
138
from bzrlib.trace import mutter, note
139
from bzrlib.osutils import format_delta, rand_chars, get_host_name
140
from bzrlib.i18n import gettext
142
from bzrlib.lazy_import import lazy_import
143
lazy_import(globals(), """
144
from bzrlib import rio
114
from bzrlib.transport import Transport
115
from bzrlib.osutils import rand_chars
116
from bzrlib.rio import RioWriter, read_stanza, Stanza
147
118
# XXX: At the moment there is no consideration of thread safety on LockDir
148
119
# objects. This should perhaps be updated - e.g. if two threads try to take a
149
120
# lock at the same time they should *both* get it. But then that's unlikely
150
121
# to be a good idea.
123
# TODO: Transport could offer a simpler put() method that avoids the
124
# rename-into-place for cases like creating the lock template, where there is
125
# no chance that the file already exists.
152
127
# TODO: Perhaps store some kind of note like the bzr command line in the lock
158
133
# TODO: Make sure to pass the right file and directory mode bits to all
159
134
# files/dirs created.
162
_DEFAULT_TIMEOUT_SECONDS = 30
163
_DEFAULT_POLL_SECONDS = 1.0
166
class LockDir(lock.Lock):
167
"""Write-lock guarding access to data.
136
_DEFAULT_TIMEOUT_SECONDS = 300
137
_DEFAULT_POLL_SECONDS = 0.5
139
class LockDir(object):
140
"""Write-lock guarding access to data."""
170
142
__INFO_NAME = '/info'
172
def __init__(self, transport, path, file_modebits=0644, dir_modebits=0755,
173
extra_holder_info=None):
144
def __init__(self, transport, path, file_modebits=0644, dir_modebits=0755):
174
145
"""Create a new LockDir object.
176
147
The LockDir is initially unlocked - this just creates the object.
178
149
:param transport: Transport which will contain the lock
180
:param path: Path to the lock within the base directory of the
151
:param path: Path to the lock within the base directory of the
183
:param extra_holder_info: If passed, {str:str} dict of extra or
184
updated information to insert into the info file when the lock is
154
assert isinstance(transport, Transport), \
155
("not a transport: %r" % transport)
187
156
self.transport = transport
189
158
self._lock_held = False
190
self._locked_via_token = False
191
159
self._fake_read_lock = False
192
160
self._held_dir = path + '/held'
193
161
self._held_info_path = self._held_dir + self.__INFO_NAME
194
162
self._file_modebits = file_modebits
195
163
self._dir_modebits = dir_modebits
196
self._report_function = note
197
self.extra_holder_info = extra_holder_info
198
self._warned_about_lock_holder = None
164
self.nonce = rand_chars(20)
200
166
def __repr__(self):
201
167
return '%s(%s%s)' % (self.__class__.__name__,
205
171
is_held = property(lambda self: self._lock_held)
207
def create(self, mode=None):
208
174
"""Create the on-disk lock.
210
This is typically only called when the object/directory containing the
176
This is typically only called when the object/directory containing the
211
177
directory is first created. The lock is not held when it's created.
213
self._trace("create lock directory")
215
self.transport.mkdir(self.path, mode=mode)
216
except (TransportError, PathError), e:
217
raise LockFailed(self, e)
219
def _attempt_lock(self):
220
"""Make the pending directory and attempt to rename into place.
222
If the rename succeeds, we read back the info file to check that we
225
If we fail to acquire the lock, this method is responsible for
226
cleaning up the pending directory if possible. (But it doesn't do
229
:returns: The nonce of the lock, if it was successfully acquired.
231
:raises LockContention: If the lock is held by someone else. The
232
exception contains the info of the current holder of the lock.
179
if self.transport.is_readonly():
180
raise UnlockableTransport(self.transport)
181
self.transport.mkdir(self.path)
183
def attempt_lock(self):
184
"""Take the lock; fail if it's already held.
186
If you wish to block until the lock can be obtained, call wait_lock()
234
self._trace("lock_write...")
235
start_time = time.time()
237
tmpname = self._create_pending_dir()
238
except (errors.TransportError, PathError), e:
239
self._trace("... failed to create pending dir, %s", e)
240
raise LockFailed(self, e)
243
self.transport.rename(tmpname, self._held_dir)
245
except (errors.TransportError, PathError, DirectoryNotEmpty,
246
FileExists, ResourceBusy), e:
247
self._trace("... contention, %s", e)
248
other_holder = self.peek()
249
self._trace("other holder is %r" % other_holder)
251
self._handle_lock_contention(other_holder)
253
self._remove_pending_dir(tmpname)
256
self._trace("... lock failed, %s", e)
257
self._remove_pending_dir(tmpname)
259
# We must check we really got the lock, because Launchpad's sftp
260
# server at one time had a bug were the rename would successfully
261
# move the new directory into the existing directory, which was
262
# incorrect. It's possible some other servers or filesystems will
263
# have a similar bug allowing someone to think they got the lock
264
# when it's already held.
266
# See <https://bugs.launchpad.net/bzr/+bug/498378> for one case.
268
# Strictly the check is unnecessary and a waste of time for most
269
# people, but probably worth trapping if something is wrong.
271
self._trace("after locking, info=%r", info)
273
raise LockFailed(self, "lock was renamed into place, but "
275
if info.get('nonce') != self.nonce:
276
self._trace("rename succeeded, "
277
"but lock is still held by someone else")
189
if self._fake_read_lock:
278
190
raise LockContention(self)
279
self._lock_held = True
280
self._trace("... lock succeeded after %dms",
281
(time.time() - start_time) * 1000)
284
def _handle_lock_contention(self, other_holder):
285
"""A lock we want to take is held by someone else.
287
This function can: tell the user about it; possibly detect that it's
288
safe or appropriate to steal the lock, or just raise an exception.
290
If this function returns (without raising an exception) the lock will
293
:param other_holder: A LockHeldInfo for the current holder; note that
294
it might be None if the lock can be seen to be held but the info
297
if (other_holder is not None):
298
if other_holder.is_lock_holder_known_dead():
299
if self.get_config().get('locks.steal_dead'):
300
ui.ui_factory.show_user_warning(
302
lock_url=urlutils.join(self.transport.base, self.path),
303
other_holder_info=unicode(other_holder))
304
self.force_break(other_holder)
305
self._trace("stole lock from dead holder")
191
if self.transport.is_readonly():
192
raise UnlockableTransport(self.transport)
194
tmpname = '%s/pending.%s.tmp' % (self.path, rand_chars(20))
195
self.transport.mkdir(tmpname)
197
self._prepare_info(sio)
199
self.transport.put(tmpname + self.__INFO_NAME, sio)
200
self.transport.rename(tmpname, self._held_dir)
201
self._lock_held = True
204
except (DirectoryNotEmpty, FileExists), e:
206
# fall through to here on contention
307
207
raise LockContention(self)
309
def _remove_pending_dir(self, tmpname):
310
"""Remove the pending directory
312
This is called if we failed to rename into place, so that the pending
313
dirs don't clutter up the lockdir.
315
self._trace("remove %s", tmpname)
317
self.transport.delete(tmpname + self.__INFO_NAME)
318
self.transport.rmdir(tmpname)
320
note(gettext("error removing pending lock: %s"), e)
322
def _create_pending_dir(self):
323
tmpname = '%s/%s.tmp' % (self.path, rand_chars(10))
325
self.transport.mkdir(tmpname)
327
# This may raise a FileExists exception
328
# which is okay, it will be caught later and determined
329
# to be a LockContention.
330
self._trace("lock directory does not exist, creating it")
331
self.create(mode=self._dir_modebits)
332
# After creating the lock directory, try again
333
self.transport.mkdir(tmpname)
334
info = LockHeldInfo.for_this_process(self.extra_holder_info)
335
self.nonce = info.get('nonce')
336
# We use put_file_non_atomic because we just created a new unique
337
# directory so we don't have to worry about files existing there.
338
# We'll rename the whole directory into place to get atomic
340
self.transport.put_bytes_non_atomic(tmpname + self.__INFO_NAME,
344
@only_raises(LockNotHeld, LockBroken)
345
209
def unlock(self):
346
210
"""Release a held lock
349
213
self._fake_read_lock = False
351
215
if not self._lock_held:
352
return lock.cant_unlock_not_held(self)
353
if self._locked_via_token:
354
self._locked_via_token = False
355
self._lock_held = False
357
old_nonce = self.nonce
358
# rename before deleting, because we can't atomically remove the
360
start_time = time.time()
361
self._trace("unlocking")
362
tmpname = '%s/releasing.%s.tmp' % (self.path, rand_chars(20))
363
# gotta own it to unlock
365
self.transport.rename(self._held_dir, tmpname)
366
self._lock_held = False
367
self.transport.delete(tmpname + self.__INFO_NAME)
369
self.transport.rmdir(tmpname)
370
except DirectoryNotEmpty, e:
371
# There might have been junk left over by a rename that moved
372
# another locker within the 'held' directory. do a slower
373
# deletion where we list the directory and remove everything
376
# Maybe this should be broader to allow for ftp servers with
377
# non-specific error messages?
378
self._trace("doing recursive deletion of non-empty directory "
380
self.transport.delete_tree(tmpname)
381
self._trace("... unlock succeeded after %dms",
382
(time.time() - start_time) * 1000)
383
result = lock.LockResult(self.transport.abspath(self.path),
385
for hook in self.hooks['lock_released']:
388
def break_lock(self):
389
"""Break a lock not held by this instance of LockDir.
391
This is a UI centric function: it uses the ui.ui_factory to
392
prompt for input if a lock is detected and there is any doubt about
393
it possibly being still active. force_break is the non-interactive
396
:returns: LockResult for the broken lock.
398
self._check_not_locked()
400
holder_info = self.peek()
401
except LockCorrupt, e:
402
# The lock info is corrupt.
403
if ui.ui_factory.get_boolean(u"Break (corrupt %r)" % (self,)):
404
self.force_break_corrupt(e.file_data)
406
if holder_info is not None:
407
if ui.ui_factory.confirm_action(
408
u"Break %(lock_info)s",
409
'bzrlib.lockdir.break',
410
dict(lock_info=unicode(holder_info))):
411
result = self.force_break(holder_info)
412
ui.ui_factory.show_message(
413
"Broke lock %s" % result.lock_url)
216
raise LockNotHeld(self)
217
# rename before deleting, because we can't atomically remove the whole
219
tmpname = '%s/releasing.%s.tmp' % (self.path, rand_chars(20))
220
self.transport.rename(self._held_dir, tmpname)
221
self._lock_held = False
222
self.transport.delete(tmpname + self.__INFO_NAME)
223
self.transport.rmdir(tmpname)
415
225
def force_break(self, dead_holder_info):
416
226
"""Release a lock held by another process.
451
259
raise LockBreakMismatch(self, broken_info, dead_holder_info)
452
260
self.transport.delete(broken_info_path)
453
261
self.transport.rmdir(tmpname)
454
result = lock.LockResult(self.transport.abspath(self.path),
455
current_info.get('nonce'))
456
for hook in self.hooks['lock_broken']:
460
def force_break_corrupt(self, corrupt_info_lines):
461
"""Release a lock that has been corrupted.
463
This is very similar to force_break, it except it doesn't assume that
464
self.peek() can work.
466
:param corrupt_info_lines: the lines of the corrupted info file, used
467
to check that the lock hasn't changed between reading the (corrupt)
468
info file and calling force_break_corrupt.
470
# XXX: this copes with unparseable info files, but what about missing
471
# info files? Or missing lock dirs?
472
self._check_not_locked()
473
tmpname = '%s/broken.%s.tmp' % (self.path, rand_chars(20))
474
self.transport.rename(self._held_dir, tmpname)
475
# check that we actually broke the right lock, not someone else;
476
# there's a small race window between checking it and doing the
478
broken_info_path = tmpname + self.__INFO_NAME
479
broken_content = self.transport.get_bytes(broken_info_path)
480
broken_lines = osutils.split_lines(broken_content)
481
if broken_lines != corrupt_info_lines:
482
raise LockBreakMismatch(self, broken_lines, corrupt_info_lines)
483
self.transport.delete(broken_info_path)
484
self.transport.rmdir(tmpname)
485
result = lock.LockResult(self.transport.abspath(self.path))
486
for hook in self.hooks['lock_broken']:
489
def _check_not_locked(self):
490
"""If the lock is held by this instance, raise an error."""
492
raise AssertionError("can't break own lock: %r" % self)
494
263
def confirm(self):
495
264
"""Make sure that the lock is still held by this locker.
510
279
if info.get('nonce') != self.nonce:
511
280
# there is a lock, but not ours
512
281
raise LockBroken(self)
514
283
def _read_info_file(self, path):
515
284
"""Read one given info file.
517
286
peek() reads the info file of the lock holder, if any.
519
return LockHeldInfo.from_info_file_bytes(
520
self.transport.get_bytes(path))
288
return self._parse_info(self.transport.get(path))
523
291
"""Check if the lock is held by anyone.
525
If it is held, this returns the lock info structure as a dict
293
If it is held, this returns the lock info structure as a rio Stanza,
526
294
which contains some information about the current lock holder.
527
295
Otherwise returns None.
530
298
info = self._read_info_file(self._held_info_path)
531
self._trace("peek -> held")
299
assert isinstance(info, dict), \
300
"bad parse result %r" % info
533
302
except NoSuchFile, e:
534
self._trace("peek -> not held")
536
def _prepare_info(self):
305
def _prepare_info(self, outf):
537
306
"""Write information about a pending lock to a temporary file.
540
def attempt_lock(self):
541
"""Take the lock; fail if it's already held.
543
If you wish to block until the lock can be obtained, call wait_lock()
546
:return: The lock token.
547
:raises LockContention: if the lock is held by someone else.
549
if self._fake_read_lock:
550
raise LockContention(self)
551
result = self._attempt_lock()
552
hook_result = lock.LockResult(self.transport.abspath(self.path),
554
for hook in self.hooks['lock_acquired']:
558
def lock_url_for_display(self):
559
"""Give a nicely-printable representation of the URL of this lock."""
560
# As local lock urls are correct we display them.
561
# We avoid displaying remote lock urls.
562
lock_url = self.transport.abspath(self.path)
563
if lock_url.startswith('file://'):
564
lock_url = lock_url.split('.bzr/')[0]
569
def wait_lock(self, timeout=None, poll=None, max_attempts=None):
309
# XXX: is creating this here inefficient?
310
config = bzrlib.config.GlobalConfig()
311
s = Stanza(hostname=socket.gethostname(),
312
pid=str(os.getpid()),
313
start_time=str(int(time.time())),
315
user=config.user_email(),
317
RioWriter(outf).write_stanza(s)
319
def _parse_info(self, info_file):
320
return read_stanza(info_file.readlines()).as_dict()
322
def wait_lock(self, timeout=_DEFAULT_TIMEOUT_SECONDS,
323
poll=_DEFAULT_POLL_SECONDS):
570
324
"""Wait a certain period for a lock.
572
326
If the lock can be acquired within the bounded time, it
574
328
is raised. Either way, this function should return within
575
329
approximately `timeout` seconds. (It may be a bit more if
576
330
a transport operation takes a long time to complete.)
578
:param timeout: Approximate maximum amount of time to wait for the
581
:param poll: Delay in seconds between retrying the lock.
583
:param max_attempts: Maximum number of times to try to lock.
585
:return: The lock token.
588
timeout = _DEFAULT_TIMEOUT_SECONDS
590
poll = _DEFAULT_POLL_SECONDS
591
# XXX: the transport interface doesn't let us guard against operations
592
# there taking a long time, so the total elapsed time or poll interval
593
# may be more than was requested.
332
# XXX: the transport interface doesn't let us guard
333
# against operations there taking a long time.
594
334
deadline = time.time() + timeout
598
lock_url = self.lock_url_for_display()
602
return self.attempt_lock()
603
339
except LockContention:
604
# possibly report the blockage, then try again
606
# TODO: In a few cases, we find out that there's contention by
607
# reading the held info and observing that it's not ours. In
608
# those cases it's a bit redundant to read it again. However,
609
# the normal case (??) is that the rename fails and so we
610
# don't know who holds the lock. For simplicity we peek
612
new_info = self.peek()
613
if new_info is not None and new_info != last_info:
614
if last_info is None:
615
start = gettext('Unable to obtain')
617
start = gettext('Lock owner changed for')
619
msg = gettext('{0} lock {1} {2}.').format(start, lock_url,
621
if deadline_str is None:
622
deadline_str = time.strftime('%H:%M:%S',
623
time.localtime(deadline))
625
msg += '\n' + gettext(
626
'Will continue to try until %s, unless '
627
'you press Ctrl-C.') % deadline_str
628
msg += '\n' + gettext('See "bzr help break-lock" for more.')
629
self._report_function(msg)
630
if (max_attempts is not None) and (attempt_count >= max_attempts):
631
self._trace("exceeded %d attempts")
632
raise LockContention(self)
633
341
if time.time() + poll < deadline:
634
self._trace("waiting %ss", poll)
637
# As timeout is always 0 for remote locks
638
# this block is applicable only for local
640
self._trace("timeout after waiting %ss", timeout)
641
raise LockContention('(local)', lock_url)
643
def leave_in_place(self):
644
self._locked_via_token = True
646
def dont_leave_in_place(self):
647
self._locked_via_token = False
649
def lock_write(self, token=None):
650
"""Wait for and acquire the lock.
652
:param token: if this is already locked, then lock_write will fail
653
unless the token matches the existing lock.
654
:returns: a token if this instance supports tokens, otherwise None.
655
:raises TokenLockingNotSupported: when a token is given but this
656
instance doesn't support using token locks.
657
:raises MismatchedToken: if the specified token doesn't match the token
658
of the existing lock.
660
A token should be passed in if you know that you have locked the object
661
some other way, and need to synchronise this object's state with that
664
XXX: docstring duplicated from LockableFiles.lock_write.
666
if token is not None:
667
self.validate_token(token)
669
self._lock_held = True
670
self._locked_via_token = True
673
return self.wait_lock()
344
raise LockContention(self)
346
def lock_write(self):
347
"""Wait for and acquire the lock."""
675
350
def lock_read(self):
676
"""Compatibility-mode shared lock.
351
"""Compatability-mode shared lock.
678
LockDir doesn't support shared read-only locks, so this
353
LockDir doesn't support shared read-only locks, so this
679
354
just pretends that the lock is taken but really does nothing.
681
# At the moment Branches are commonly locked for read, but
356
# At the moment Branches are commonly locked for read, but
682
357
# we can't rely on that remotely. Once this is cleaned up,
683
# reenable this warning to prevent it coming back in
358
# reenable this warning to prevent it coming back in
684
359
# -- mbp 20060303
685
360
## warn("LockDir.lock_read falls back to write lock")
686
361
if self._lock_held or self._fake_read_lock:
687
362
raise LockContention(self)
688
363
self._fake_read_lock = True
690
def validate_token(self, token):
691
if token is not None:
697
lock_token = info.get('nonce')
698
if token != lock_token:
699
raise errors.TokenMismatch(token, lock_token)
701
self._trace("revalidated by token %r", token)
703
def _trace(self, format, *args):
704
if 'lock' not in debug.debug_flags:
706
mutter(str(self) + ": " + (format % args))
708
def get_config(self):
709
"""Get the configuration that governs this lockdir."""
710
# XXX: This really should also use the locationconfig at least, but
711
# that seems a bit hard to hook up at the moment. -- mbp 20110329
712
# FIXME: The above is still true ;) -- vila 20110811
713
return config.GlobalStack()
716
class LockHeldInfo(object):
717
"""The information recorded about a held lock.
719
This information is recorded into the lock when it's taken, and it can be
720
read back by any process with access to the lockdir. It can be used, for
721
example, to tell the user who holds the lock, or to try to detect whether
722
the lock holder is still alive.
724
Prior to bzr 2.4 a simple dict was used instead of an object.
727
def __init__(self, info_dict):
728
self.info_dict = info_dict
731
"""Return a debugging representation of this object."""
732
return "%s(%r)" % (self.__class__.__name__, self.info_dict)
734
def __unicode__(self):
735
"""Return a user-oriented description of this object."""
736
d = self.to_readable_dict()
738
u'held by %(user)s on %(hostname)s (process #%(pid)s), '
739
u'acquired %(time_ago)s') % d)
741
def to_readable_dict(self):
742
"""Turn the holder info into a dict of human-readable attributes.
744
For example, the start time is presented relative to the current time,
745
rather than as seconds since the epoch.
747
Returns a list of [user, hostname, pid, time_ago] all as readable
750
start_time = self.info_dict.get('start_time')
751
if start_time is None:
752
time_ago = '(unknown)'
754
time_ago = format_delta(
755
time.time() - int(self.info_dict['start_time']))
756
user = self.info_dict.get('user', '<unknown>')
757
hostname = self.info_dict.get('hostname', '<unknown>')
758
pid = self.info_dict.get('pid', '<unknown>')
765
def get(self, field_name):
766
"""Return the contents of a field from the lock info, or None."""
767
return self.info_dict.get(field_name)
770
def for_this_process(cls, extra_holder_info):
771
"""Return a new LockHeldInfo for a lock taken by this process.
774
hostname=get_host_name(),
775
pid=str(os.getpid()),
776
nonce=rand_chars(20),
777
start_time=str(int(time.time())),
778
user=get_username_for_lock_info(),
780
if extra_holder_info is not None:
781
info.update(extra_holder_info)
785
s = rio.Stanza(**self.info_dict)
789
def from_info_file_bytes(cls, info_file_bytes):
790
"""Construct from the contents of the held file."""
791
lines = osutils.split_lines(info_file_bytes)
793
stanza = rio.read_stanza(lines)
794
except ValueError, e:
795
mutter('Corrupt lock info file: %r', lines)
796
raise LockCorrupt("could not parse lock info file: " + str(e),
799
# see bug 185013; we fairly often end up with the info file being
800
# empty after an interruption; we could log a message here but
801
# there may not be much we can say
804
return cls(stanza.as_dict())
806
def __cmp__(self, other):
807
"""Value comparison of lock holders."""
809
cmp(type(self), type(other))
810
or cmp(self.info_dict, other.info_dict))
812
def is_locked_by_this_process(self):
813
"""True if this process seems to be the current lock holder."""
815
self.get('hostname') == get_host_name()
816
and self.get('pid') == str(os.getpid())
817
and self.get('user') == get_username_for_lock_info())
819
def is_lock_holder_known_dead(self):
820
"""True if the lock holder process is known to be dead.
822
False if it's either known to be still alive, or if we just can't tell.
824
We can be fairly sure the lock holder is dead if it declared the same
825
hostname and there is no process with the given pid alive. If people
826
have multiple machines with the same hostname this may cause trouble.
828
This doesn't check whether the lock holder is in fact the same process
829
calling this method. (In that case it will return true.)
831
if self.get('hostname') != get_host_name():
833
if self.get('hostname') == 'localhost':
836
if self.get('user') != get_username_for_lock_info():
837
# Could well be another local process by a different user, but
838
# just to be safe we won't conclude about this either.
840
pid_str = self.info_dict.get('pid', None)
842
mutter("no pid recorded in %r" % (self, ))
847
mutter("can't parse pid %r from %r"
850
return osutils.is_local_pid_dead(pid)
853
def get_username_for_lock_info():
854
"""Get a username suitable for putting into a lock.
856
It's ok if what's written here is not a proper email address as long
857
as it gives some clue who the user is.
860
return config.GlobalConfig().username()
861
except errors.NoWhoami:
862
return osutils.getuser_unicode()
365
def wait(self, timeout=20, poll=0.5):
366
"""Wait a certain period for a lock to be released."""
367
# XXX: the transport interface doesn't let us guard
368
# against operations there taking a long time.
369
deadline = time.time() + timeout
373
if time.time() + poll < deadline:
376
raise LockContention(self)
added
removed
bzrlib/lockdir.py
