88
88
>>> t = MemoryTransport()
89
89
>>> l = LockDir(t, 'sample-lock')
91
>>> token = l.wait_lock()
92
92
>>> # do something here
98
# TODO: We sometimes have the problem that our attempt to rename '1234' to
99
# 'held' fails because the transport server moves into an existing directory,
100
# rather than failing the rename. If we made the info file name the same as
101
# the locked directory name we would avoid this problem because moving into
102
# the held directory would implicitly clash. However this would not mesh with
103
# the existing locking code and needs a new format of the containing object.
104
# -- robertc, mbp 20070628
99
from cStringIO import StringIO
115
101
import bzrlib.config
116
from bzrlib.decorators import only_raises
117
102
from bzrlib.errors import (
118
103
DirectoryNotEmpty,
120
105
LockBreakMismatch,
130
114
from bzrlib.trace import mutter, note
131
from bzrlib.osutils import format_delta, rand_chars, get_host_name
115
from bzrlib.transport import Transport
116
from bzrlib.osutils import rand_chars, format_delta
117
from bzrlib.rio import read_stanza, Stanza
134
from bzrlib.lazy_import import lazy_import
135
lazy_import(globals(), """
136
from bzrlib import rio
139
120
# XXX: At the moment there is no consideration of thread safety on LockDir
140
121
# objects. This should perhaps be updated - e.g. if two threads try to take a
193
175
def create(self, mode=None):
194
176
"""Create the on-disk lock.
196
This is typically only called when the object/directory containing the
178
This is typically only called when the object/directory containing the
197
179
directory is first created. The lock is not held when it's created.
199
self._trace("create lock directory")
201
self.transport.mkdir(self.path, mode=mode)
202
except (TransportError, PathError), e:
203
raise LockFailed(self, e)
206
def _attempt_lock(self):
207
"""Make the pending directory and attempt to rename into place.
209
If the rename succeeds, we read back the info file to check that we
212
If we fail to acquire the lock, this method is responsible for
213
cleaning up the pending directory if possible. (But it doesn't do
216
:returns: The nonce of the lock, if it was successfully acquired.
218
:raises LockContention: If the lock is held by someone else. The exception
219
contains the info of the current holder of the lock.
181
if self.transport.is_readonly():
182
raise UnlockableTransport(self.transport)
183
self.transport.mkdir(self.path, mode=mode)
185
def attempt_lock(self):
186
"""Take the lock; fail if it's already held.
188
If you wish to block until the lock can be obtained, call wait_lock()
221
self._trace("lock_write...")
222
start_time = time.time()
224
tmpname = self._create_pending_dir()
225
except (errors.TransportError, PathError), e:
226
self._trace("... failed to create pending dir, %s", e)
227
raise LockFailed(self, e)
191
if self._fake_read_lock:
192
raise LockContention(self)
193
if self.transport.is_readonly():
194
raise UnlockableTransport(self.transport)
196
tmpname = '%s/pending.%s.tmp' % (self.path, rand_chars(20))
198
self.transport.mkdir(tmpname)
200
# This may raise a FileExists exception
201
# which is okay, it will be caught later and determined
202
# to be a LockContention.
203
self.create(mode=self._dir_modebits)
205
# After creating the lock directory, try again
206
self.transport.mkdir(tmpname)
208
info_bytes = self._prepare_info()
209
# We use put_file_non_atomic because we just created a new unique
210
# directory so we don't have to worry about files existing there.
211
# We'll rename the whole directory into place to get atomic
213
self.transport.put_bytes_non_atomic(tmpname + self.__INFO_NAME,
229
216
self.transport.rename(tmpname, self._held_dir)
230
except (errors.TransportError, PathError, DirectoryNotEmpty,
231
FileExists, ResourceBusy), e:
232
self._trace("... contention, %s", e)
233
self._remove_pending_dir(tmpname)
234
raise LockContention(self)
236
self._trace("... lock failed, %s", e)
237
self._remove_pending_dir(tmpname)
239
# We must check we really got the lock, because Launchpad's sftp
240
# server at one time had a bug were the rename would successfully
241
# move the new directory into the existing directory, which was
242
# incorrect. It's possible some other servers or filesystems will
243
# have a similar bug allowing someone to think they got the lock
244
# when it's already held.
246
# See <https://bugs.edge.launchpad.net/bzr/+bug/498378> for one case.
248
# Strictly the check is unnecessary and a waste of time for most
249
# people, but probably worth trapping if something is wrong.
251
self._trace("after locking, info=%r", info)
253
raise LockFailed(self, "lock was renamed into place, but "
255
if info.get('nonce') != self.nonce:
256
self._trace("rename succeeded, "
257
"but lock is still held by someone else")
258
raise LockContention(self)
259
self._lock_held = True
260
self._trace("... lock succeeded after %dms",
261
(time.time() - start_time) * 1000)
264
def _remove_pending_dir(self, tmpname):
265
"""Remove the pending directory
267
This is called if we failed to rename into place, so that the pending
268
dirs don't clutter up the lockdir.
270
self._trace("remove %s", tmpname)
272
self.transport.delete(tmpname + self.__INFO_NAME)
273
self.transport.rmdir(tmpname)
275
note("error removing pending lock: %s", e)
277
def _create_pending_dir(self):
278
tmpname = '%s/%s.tmp' % (self.path, rand_chars(10))
280
self.transport.mkdir(tmpname)
282
# This may raise a FileExists exception
283
# which is okay, it will be caught later and determined
284
# to be a LockContention.
285
self._trace("lock directory does not exist, creating it")
286
self.create(mode=self._dir_modebits)
287
# After creating the lock directory, try again
288
self.transport.mkdir(tmpname)
289
self.nonce = rand_chars(20)
290
info_bytes = self._prepare_info()
291
# We use put_file_non_atomic because we just created a new unique
292
# directory so we don't have to worry about files existing there.
293
# We'll rename the whole directory into place to get atomic
295
self.transport.put_bytes_non_atomic(tmpname + self.__INFO_NAME,
299
@only_raises(LockNotHeld, LockBroken)
217
self._lock_held = True
219
except (PathError, DirectoryNotEmpty, FileExists, ResourceBusy), e:
220
mutter("contention on %r: %s", self, e)
221
raise LockContention(self)
300
223
def unlock(self):
301
224
"""Release a held lock
304
227
self._fake_read_lock = False
306
229
if not self._lock_held:
307
return lock.cant_unlock_not_held(self)
308
if self._locked_via_token:
309
self._locked_via_token = False
310
self._lock_held = False
312
old_nonce = self.nonce
313
# rename before deleting, because we can't atomically remove the
315
start_time = time.time()
316
self._trace("unlocking")
317
tmpname = '%s/releasing.%s.tmp' % (self.path, rand_chars(20))
318
# gotta own it to unlock
320
self.transport.rename(self._held_dir, tmpname)
321
self._lock_held = False
322
self.transport.delete(tmpname + self.__INFO_NAME)
324
self.transport.rmdir(tmpname)
325
except DirectoryNotEmpty, e:
326
# There might have been junk left over by a rename that moved
327
# another locker within the 'held' directory. do a slower
328
# deletion where we list the directory and remove everything
331
# Maybe this should be broader to allow for ftp servers with
332
# non-specific error messages?
333
self._trace("doing recursive deletion of non-empty directory "
335
self.transport.delete_tree(tmpname)
336
self._trace("... unlock succeeded after %dms",
337
(time.time() - start_time) * 1000)
338
result = lock.LockResult(self.transport.abspath(self.path),
340
for hook in self.hooks['lock_released']:
230
raise LockNotHeld(self)
231
# rename before deleting, because we can't atomically remove the whole
233
tmpname = '%s/releasing.%s.tmp' % (self.path, rand_chars(20))
234
# gotta own it to unlock
236
self.transport.rename(self._held_dir, tmpname)
237
self._lock_held = False
238
self.transport.delete(tmpname + self.__INFO_NAME)
239
self.transport.rmdir(tmpname)
343
241
def break_lock(self):
344
242
"""Break a lock not held by this instance of LockDir.
419
313
if info.get('nonce') != self.nonce:
420
314
# there is a lock, but not ours
421
315
raise LockBroken(self)
423
317
def _read_info_file(self, path):
424
318
"""Read one given info file.
426
320
peek() reads the info file of the lock holder, if any.
428
return self._parse_info(self.transport.get_bytes(path))
322
return self._parse_info(self.transport.get(path))
431
325
"""Check if the lock is held by anyone.
433
If it is held, this returns the lock info structure as a dict
327
If it is held, this returns the lock info structure as a rio Stanza,
434
328
which contains some information about the current lock holder.
435
329
Otherwise returns None.
438
332
info = self._read_info_file(self._held_info_path)
439
self._trace("peek -> held")
333
assert isinstance(info, dict), \
334
"bad parse result %r" % info
441
336
except NoSuchFile, e:
442
self._trace("peek -> not held")
444
339
def _prepare_info(self):
445
340
"""Write information about a pending lock to a temporary file.
447
343
# XXX: is creating this here inefficient?
448
344
config = bzrlib.config.GlobalConfig()
450
user = config.user_email()
451
except errors.NoEmailInUsername:
452
user = config.username()
453
s = rio.Stanza(hostname=get_host_name(),
345
s = Stanza(hostname=socket.gethostname(),
454
346
pid=str(os.getpid()),
455
347
start_time=str(int(time.time())),
456
348
nonce=self.nonce,
349
user=config.user_email(),
459
351
return s.to_string()
461
def _parse_info(self, info_bytes):
462
stanza = rio.read_stanza(osutils.split_lines(info_bytes))
464
# see bug 185013; we fairly often end up with the info file being
465
# empty after an interruption; we could log a message here but
466
# there may not be much we can say
469
return stanza.as_dict()
471
def attempt_lock(self):
472
"""Take the lock; fail if it's already held.
474
If you wish to block until the lock can be obtained, call wait_lock()
477
:return: The lock token.
478
:raises LockContention: if the lock is held by someone else.
480
if self._fake_read_lock:
481
raise LockContention(self)
482
result = self._attempt_lock()
483
hook_result = lock.LockResult(self.transport.abspath(self.path),
485
for hook in self.hooks['lock_acquired']:
489
def wait_lock(self, timeout=None, poll=None, max_attempts=None):
353
def _parse_info(self, info_file):
354
return read_stanza(info_file.readlines()).as_dict()
356
def wait_lock(self, timeout=None, poll=None):
490
357
"""Wait a certain period for a lock.
492
359
If the lock can be acquired within the bounded time, it
494
361
is raised. Either way, this function should return within
495
362
approximately `timeout` seconds. (It may be a bit more if
496
363
a transport operation takes a long time to complete.)
498
:param timeout: Approximate maximum amount of time to wait for the
501
:param poll: Delay in seconds between retrying the lock.
503
:param max_attempts: Maximum number of times to try to lock.
505
:return: The lock token.
507
365
if timeout is None:
508
366
timeout = _DEFAULT_TIMEOUT_SECONDS
510
368
poll = _DEFAULT_POLL_SECONDS
511
# XXX: the transport interface doesn't let us guard against operations
512
# there taking a long time, so the total elapsed time or poll interval
513
# may be more than was requested.
370
# XXX: the transport interface doesn't let us guard
371
# against operations there taking a long time.
514
372
deadline = time.time() + timeout
515
373
deadline_str = None
521
return self.attempt_lock()
522
379
except LockContention:
523
# possibly report the blockage, then try again
525
# TODO: In a few cases, we find out that there's contention by
526
# reading the held info and observing that it's not ours. In
527
# those cases it's a bit redundant to read it again. However,
528
# the normal case (??) is that the rename fails and so we
529
# don't know who holds the lock. For simplicity we peek
531
381
new_info = self.peek()
382
mutter('last_info: %s, new info: %s', last_info, new_info)
532
383
if new_info is not None and new_info != last_info:
533
384
if last_info is None:
534
385
start = 'Unable to obtain'
539
390
if deadline_str is None:
540
391
deadline_str = time.strftime('%H:%M:%S',
541
392
time.localtime(deadline))
542
lock_url = self.transport.abspath(self.path)
543
# See <https://bugs.edge.launchpad.net/bzr/+bug/250451>
544
# the URL here is sometimes not one that is useful to the
545
# user, perhaps being wrapped in a lp-%d or chroot decorator,
546
# especially if this error is issued from the server.
547
393
self._report_function('%s %s\n'
549
'%s\n' # locked ... ago
550
'Will continue to try until %s, unless '
551
'you press Ctrl-C.\n'
552
'See "bzr help break-lock" for more.',
395
'%s\n' # locked ... ago
396
'Will continue to try until %s\n',
560
if (max_attempts is not None) and (attempt_count >= max_attempts):
561
self._trace("exceeded %d attempts")
562
raise LockContention(self)
563
403
if time.time() + poll < deadline:
564
self._trace("waiting %ss", poll)
567
self._trace("timeout after waiting %ss", timeout)
568
406
raise LockContention(self)
570
def leave_in_place(self):
571
self._locked_via_token = True
573
def dont_leave_in_place(self):
574
self._locked_via_token = False
576
def lock_write(self, token=None):
577
"""Wait for and acquire the lock.
579
:param token: if this is already locked, then lock_write will fail
580
unless the token matches the existing lock.
581
:returns: a token if this instance supports tokens, otherwise None.
582
:raises TokenLockingNotSupported: when a token is given but this
583
instance doesn't support using token locks.
584
:raises MismatchedToken: if the specified token doesn't match the token
585
of the existing lock.
587
A token should be passed in if you know that you have locked the object
588
some other way, and need to synchronise this object's state with that
591
XXX: docstring duplicated from LockableFiles.lock_write.
593
if token is not None:
594
self.validate_token(token)
596
self._lock_held = True
597
self._locked_via_token = True
600
return self.wait_lock()
408
def lock_write(self):
409
"""Wait for and acquire the lock."""
602
412
def lock_read(self):
603
413
"""Compatibility-mode shared lock.
605
LockDir doesn't support shared read-only locks, so this
415
LockDir doesn't support shared read-only locks, so this
606
416
just pretends that the lock is taken but really does nothing.
608
# At the moment Branches are commonly locked for read, but
418
# At the moment Branches are commonly locked for read, but
609
419
# we can't rely on that remotely. Once this is cleaned up,
610
# reenable this warning to prevent it coming back in
420
# reenable this warning to prevent it coming back in
611
421
# -- mbp 20060303
612
422
## warn("LockDir.lock_read falls back to write lock")
613
423
if self._lock_held or self._fake_read_lock:
614
424
raise LockContention(self)
615
425
self._fake_read_lock = True
427
def wait(self, timeout=20, poll=0.5):
428
"""Wait a certain period for a lock to be released."""
429
# XXX: the transport interface doesn't let us guard
430
# against operations there taking a long time.
431
deadline = time.time() + timeout
435
if time.time() + poll < deadline:
438
raise LockContention(self)
617
440
def _format_lock_info(self, info):
618
441
"""Turn the contents of peek() into something for the user"""
619
442
lock_url = self.transport.abspath(self.path)
620
start_time = info.get('start_time')
621
if start_time is None:
622
time_ago = '(unknown)'
624
time_ago = format_delta(time.time() - int(info['start_time']))
443
delta = time.time() - int(info['start_time'])
626
445
'lock %s' % (lock_url,),
627
'held by %s on host %s [process #%s]' %
628
tuple([info.get(x, '<unknown>') for x in ['user', 'hostname', 'pid']]),
629
'locked %s' % (time_ago,),
446
'held by %(user)s on host %(hostname)s [process #%(pid)s]' % info,
447
'locked %s' % (format_delta(delta),),
632
def validate_token(self, token):
633
if token is not None:
639
lock_token = info.get('nonce')
640
if token != lock_token:
641
raise errors.TokenMismatch(token, lock_token)
643
self._trace("revalidated by token %r", token)
645
def _trace(self, format, *args):
646
if 'lock' not in debug.debug_flags:
648
mutter(str(self) + ": " + (format % args))