root / lib / locking.py @ d868edb4
History | View | Annotate | Download (29.7 kB)
1 |
#
|
---|---|
2 |
#
|
3 |
|
4 |
# Copyright (C) 2006, 2007 Google Inc.
|
5 |
#
|
6 |
# This program is free software; you can redistribute it and/or modify
|
7 |
# it under the terms of the GNU General Public License as published by
|
8 |
# the Free Software Foundation; either version 2 of the License, or
|
9 |
# (at your option) any later version.
|
10 |
#
|
11 |
# This program is distributed in the hope that it will be useful, but
|
12 |
# WITHOUT ANY WARRANTY; without even the implied warranty of
|
13 |
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
14 |
# General Public License for more details.
|
15 |
#
|
16 |
# You should have received a copy of the GNU General Public License
|
17 |
# along with this program; if not, write to the Free Software
|
18 |
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
|
19 |
# 02110-1301, USA.
|
20 |
|
21 |
"""Module implementing the Ganeti locking code."""
|
22 |
|
23 |
# pylint: disable-msg=W0613,W0201
|
24 |
|
25 |
import threading |
26 |
# Wouldn't it be better to define LockingError in the locking module?
|
27 |
# Well, for now that's how the rest of the code does it...
|
28 |
from ganeti import errors |
29 |
from ganeti import utils |
30 |
|
31 |
|
32 |
def ssynchronized(lock, shared=0): |
33 |
"""Shared Synchronization decorator.
|
34 |
|
35 |
Calls the function holding the given lock, either in exclusive or shared
|
36 |
mode. It requires the passed lock to be a SharedLock (or support its
|
37 |
semantics).
|
38 |
|
39 |
"""
|
40 |
def wrap(fn): |
41 |
def sync_function(*args, **kwargs): |
42 |
lock.acquire(shared=shared) |
43 |
try:
|
44 |
return fn(*args, **kwargs)
|
45 |
finally:
|
46 |
lock.release() |
47 |
return sync_function
|
48 |
return wrap
|
49 |
|
50 |
|
51 |
class SharedLock: |
52 |
"""Implements a shared lock.
|
53 |
|
54 |
Multiple threads can acquire the lock in a shared way, calling
|
55 |
acquire_shared(). In order to acquire the lock in an exclusive way threads
|
56 |
can call acquire_exclusive().
|
57 |
|
58 |
The lock prevents starvation but does not guarantee that threads will acquire
|
59 |
the shared lock in the order they queued for it, just that they will
|
60 |
eventually do so.
|
61 |
|
62 |
"""
|
63 |
def __init__(self): |
64 |
"""Construct a new SharedLock"""
|
65 |
# we have two conditions, c_shr and c_exc, sharing the same lock.
|
66 |
self.__lock = threading.Lock()
|
67 |
self.__turn_shr = threading.Condition(self.__lock) |
68 |
self.__turn_exc = threading.Condition(self.__lock) |
69 |
|
70 |
# current lock holders
|
71 |
self.__shr = set() |
72 |
self.__exc = None |
73 |
|
74 |
# lock waiters
|
75 |
self.__nwait_exc = 0 |
76 |
self.__nwait_shr = 0 |
77 |
self.__npass_shr = 0 |
78 |
|
79 |
# is this lock in the deleted state?
|
80 |
self.__deleted = False |
81 |
|
82 |
def __is_sharer(self): |
83 |
"""Is the current thread sharing the lock at this time?"""
|
84 |
return threading.currentThread() in self.__shr |
85 |
|
86 |
def __is_exclusive(self): |
87 |
"""Is the current thread holding the lock exclusively at this time?"""
|
88 |
return threading.currentThread() == self.__exc |
89 |
|
90 |
def __is_owned(self, shared=-1): |
91 |
"""Is the current thread somehow owning the lock at this time?
|
92 |
|
93 |
This is a private version of the function, which presumes you're holding
|
94 |
the internal lock.
|
95 |
|
96 |
"""
|
97 |
if shared < 0: |
98 |
return self.__is_sharer() or self.__is_exclusive() |
99 |
elif shared:
|
100 |
return self.__is_sharer() |
101 |
else:
|
102 |
return self.__is_exclusive() |
103 |
|
104 |
def _is_owned(self, shared=-1): |
105 |
"""Is the current thread somehow owning the lock at this time?
|
106 |
|
107 |
Args:
|
108 |
shared:
|
109 |
< 0: check for any type of ownership (default)
|
110 |
0: check for exclusive ownership
|
111 |
> 0: check for shared ownership
|
112 |
|
113 |
"""
|
114 |
self.__lock.acquire()
|
115 |
try:
|
116 |
result = self.__is_owned(shared=shared)
|
117 |
finally:
|
118 |
self.__lock.release()
|
119 |
|
120 |
return result
|
121 |
|
122 |
def __wait(self, c): |
123 |
"""Wait on the given condition, and raise an exception if the current lock
|
124 |
is declared deleted in the meantime.
|
125 |
|
126 |
Args:
|
127 |
c: condition to wait on
|
128 |
|
129 |
"""
|
130 |
c.wait() |
131 |
if self.__deleted: |
132 |
raise errors.LockError('deleted lock') |
133 |
|
134 |
def __exclusive_acquire(self): |
135 |
"""Acquire the lock exclusively.
|
136 |
|
137 |
This is a private function that presumes you are already holding the
|
138 |
internal lock. It's defined separately to avoid code duplication between
|
139 |
acquire() and delete()
|
140 |
|
141 |
"""
|
142 |
self.__nwait_exc += 1 |
143 |
try:
|
144 |
# This is to save ourselves from a nasty race condition that could
|
145 |
# theoretically make the sharers starve.
|
146 |
if self.__nwait_shr > 0 or self.__nwait_exc > 1: |
147 |
self.__wait(self.__turn_exc) |
148 |
|
149 |
while len(self.__shr) > 0 or self.__exc is not None: |
150 |
self.__wait(self.__turn_exc) |
151 |
|
152 |
self.__exc = threading.currentThread()
|
153 |
finally:
|
154 |
self.__nwait_exc -= 1 |
155 |
|
156 |
assert self.__npass_shr == 0, "SharedLock: internal fairness violation" |
157 |
|
158 |
def acquire(self, blocking=1, shared=0): |
159 |
"""Acquire a shared lock.
|
160 |
|
161 |
Args:
|
162 |
shared: whether to acquire in shared mode. By default an exclusive lock
|
163 |
will be acquired.
|
164 |
blocking: whether to block while trying to acquire or to operate in
|
165 |
try-lock mode. this locking mode is not supported yet.
|
166 |
|
167 |
"""
|
168 |
if not blocking: |
169 |
# We don't have non-blocking mode for now
|
170 |
raise NotImplementedError |
171 |
|
172 |
self.__lock.acquire()
|
173 |
try:
|
174 |
if self.__deleted: |
175 |
raise errors.LockError('deleted lock') |
176 |
|
177 |
# We cannot acquire the lock if we already have it
|
178 |
assert not self.__is_owned(), "double acquire() on a non-recursive lock" |
179 |
assert self.__npass_shr >= 0, "Internal fairness condition weirdness" |
180 |
|
181 |
if shared:
|
182 |
self.__nwait_shr += 1 |
183 |
try:
|
184 |
wait = False
|
185 |
# If there is an exclusive holder waiting we have to wait. We'll
|
186 |
# only do this once, though, when we start waiting for the lock. Then
|
187 |
# we'll just wait while there are no exclusive holders.
|
188 |
if self.__nwait_exc > 0: |
189 |
# TODO: if !blocking...
|
190 |
wait = True
|
191 |
self.__wait(self.__turn_shr) |
192 |
|
193 |
while self.__exc is not None: |
194 |
wait = True
|
195 |
# TODO: if !blocking...
|
196 |
self.__wait(self.__turn_shr) |
197 |
|
198 |
self.__shr.add(threading.currentThread())
|
199 |
|
200 |
# If we were waiting note that we passed
|
201 |
if wait:
|
202 |
self.__npass_shr -= 1 |
203 |
|
204 |
finally:
|
205 |
self.__nwait_shr -= 1 |
206 |
|
207 |
assert self.__npass_shr >= 0, "Internal fairness condition weirdness" |
208 |
else:
|
209 |
# TODO: if !blocking...
|
210 |
# (or modify __exclusive_acquire for non-blocking mode)
|
211 |
self.__exclusive_acquire()
|
212 |
|
213 |
finally:
|
214 |
self.__lock.release()
|
215 |
|
216 |
return True |
217 |
|
218 |
def release(self): |
219 |
"""Release a Shared Lock.
|
220 |
|
221 |
You must have acquired the lock, either in shared or in exclusive mode,
|
222 |
before calling this function.
|
223 |
|
224 |
"""
|
225 |
self.__lock.acquire()
|
226 |
try:
|
227 |
assert self.__npass_shr >= 0, "Internal fairness condition weirdness" |
228 |
# Autodetect release type
|
229 |
if self.__is_exclusive(): |
230 |
self.__exc = None |
231 |
|
232 |
# An exclusive holder has just had the lock, time to put it in shared
|
233 |
# mode if there are shared holders waiting. Otherwise wake up the next
|
234 |
# exclusive holder.
|
235 |
if self.__nwait_shr > 0: |
236 |
# Make sure at least the ones which were blocked pass.
|
237 |
self.__npass_shr = self.__nwait_shr |
238 |
self.__turn_shr.notifyAll()
|
239 |
elif self.__nwait_exc > 0: |
240 |
self.__turn_exc.notify()
|
241 |
|
242 |
elif self.__is_sharer(): |
243 |
self.__shr.remove(threading.currentThread())
|
244 |
|
245 |
# If there are shared holders waiting (and not just scheduled to pass)
|
246 |
# there *must* be an exclusive holder waiting as well; otherwise what
|
247 |
# were they waiting for?
|
248 |
assert (self.__nwait_exc > 0 or self.__npass_shr == self.__nwait_shr), \ |
249 |
"Lock sharers waiting while no exclusive is queueing"
|
250 |
|
251 |
# If there are no more shared holders either in or scheduled to pass,
|
252 |
# and some exclusive holders are waiting let's wake one up.
|
253 |
if (len(self.__shr) == 0 and |
254 |
self.__nwait_exc > 0 and |
255 |
not self.__npass_shr > 0): |
256 |
self.__turn_exc.notify()
|
257 |
|
258 |
else:
|
259 |
assert False, "Cannot release non-owned lock" |
260 |
|
261 |
finally:
|
262 |
self.__lock.release()
|
263 |
|
264 |
def delete(self, blocking=1): |
265 |
"""Delete a Shared Lock.
|
266 |
|
267 |
This operation will declare the lock for removal. First the lock will be
|
268 |
acquired in exclusive mode if you don't already own it, then the lock
|
269 |
will be put in a state where any future and pending acquire() fail.
|
270 |
|
271 |
Args:
|
272 |
blocking: whether to block while trying to acquire or to operate in
|
273 |
try-lock mode. this locking mode is not supported yet unless
|
274 |
you are already holding exclusively the lock.
|
275 |
|
276 |
"""
|
277 |
self.__lock.acquire()
|
278 |
try:
|
279 |
assert not self.__is_sharer(), "cannot delete() a lock while sharing it" |
280 |
|
281 |
if self.__deleted: |
282 |
raise errors.LockError('deleted lock') |
283 |
|
284 |
if not self.__is_exclusive(): |
285 |
if not blocking: |
286 |
# We don't have non-blocking mode for now
|
287 |
raise NotImplementedError |
288 |
self.__exclusive_acquire()
|
289 |
|
290 |
self.__deleted = True |
291 |
self.__exc = None |
292 |
# Wake up everybody, they will fail acquiring the lock and
|
293 |
# raise an exception instead.
|
294 |
self.__turn_exc.notifyAll()
|
295 |
self.__turn_shr.notifyAll()
|
296 |
|
297 |
finally:
|
298 |
self.__lock.release()
|
299 |
|
300 |
|
301 |
# Whenever we want to acquire a full LockSet we pass None as the value to acquire.
|
302 |
# Hide this behing this nicely named constant.
|
303 |
ALL_SET = None
|
304 |
|
305 |
|
306 |
class LockSet: |
307 |
"""Implements a set of locks.
|
308 |
|
309 |
This abstraction implements a set of shared locks for the same resource type,
|
310 |
distinguished by name. The user can lock a subset of the resources and the
|
311 |
LockSet will take care of acquiring the locks always in the same order, thus
|
312 |
preventing deadlock.
|
313 |
|
314 |
All the locks needed in the same set must be acquired together, though.
|
315 |
|
316 |
"""
|
317 |
def __init__(self, members=None): |
318 |
"""Constructs a new LockSet.
|
319 |
|
320 |
Args:
|
321 |
members: initial members of the set
|
322 |
|
323 |
"""
|
324 |
# Used internally to guarantee coherency.
|
325 |
self.__lock = SharedLock()
|
326 |
|
327 |
# The lockdict indexes the relationship name -> lock
|
328 |
# The order-of-locking is implied by the alphabetical order of names
|
329 |
self.__lockdict = {}
|
330 |
|
331 |
if members is not None: |
332 |
for name in members: |
333 |
self.__lockdict[name] = SharedLock()
|
334 |
|
335 |
# The owner dict contains the set of locks each thread owns. For
|
336 |
# performance each thread can access its own key without a global lock on
|
337 |
# this structure. It is paramount though that *no* other type of access is
|
338 |
# done to this structure (eg. no looping over its keys). *_owner helper
|
339 |
# function are defined to guarantee access is correct, but in general never
|
340 |
# do anything different than __owners[threading.currentThread()], or there
|
341 |
# will be trouble.
|
342 |
self.__owners = {}
|
343 |
|
344 |
def _is_owned(self): |
345 |
"""Is the current thread a current level owner?"""
|
346 |
return threading.currentThread() in self.__owners |
347 |
|
348 |
def _add_owned(self, name=None): |
349 |
"""Note the current thread owns the given lock"""
|
350 |
if name is None: |
351 |
if not self._is_owned(): |
352 |
self.__owners[threading.currentThread()] = set() |
353 |
else:
|
354 |
if self._is_owned(): |
355 |
self.__owners[threading.currentThread()].add(name)
|
356 |
else:
|
357 |
self.__owners[threading.currentThread()] = set([name]) |
358 |
|
359 |
|
360 |
def _del_owned(self, name=None): |
361 |
"""Note the current thread owns the given lock"""
|
362 |
|
363 |
if name is not None: |
364 |
self.__owners[threading.currentThread()].remove(name)
|
365 |
|
366 |
# Only remove the key if we don't hold the set-lock as well
|
367 |
if (not self.__lock._is_owned() and |
368 |
not self.__owners[threading.currentThread()]): |
369 |
del self.__owners[threading.currentThread()] |
370 |
|
371 |
def _list_owned(self): |
372 |
"""Get the set of resource names owned by the current thread"""
|
373 |
if self._is_owned(): |
374 |
return self.__owners[threading.currentThread()].copy() |
375 |
else:
|
376 |
return set() |
377 |
|
378 |
def __names(self): |
379 |
"""Return the current set of names.
|
380 |
|
381 |
Only call this function while holding __lock and don't iterate on the
|
382 |
result after releasing the lock.
|
383 |
|
384 |
"""
|
385 |
return self.__lockdict.keys() |
386 |
|
387 |
def _names(self): |
388 |
"""Return a copy of the current set of elements.
|
389 |
|
390 |
Used only for debugging purposes.
|
391 |
|
392 |
"""
|
393 |
# If we don't already own the set-level lock acquired
|
394 |
# we'll get it and note we need to release it later.
|
395 |
release_lock = False
|
396 |
if not self.__lock._is_owned(): |
397 |
release_lock = True
|
398 |
self.__lock.acquire(shared=1) |
399 |
try:
|
400 |
result = self.__names()
|
401 |
finally:
|
402 |
if release_lock:
|
403 |
self.__lock.release()
|
404 |
return set(result) |
405 |
|
406 |
def acquire(self, names, blocking=1, shared=0): |
407 |
"""Acquire a set of resource locks.
|
408 |
|
409 |
Args:
|
410 |
names: the names of the locks which shall be acquired.
|
411 |
(special lock names, or instance/node names)
|
412 |
shared: whether to acquire in shared mode. By default an exclusive lock
|
413 |
will be acquired.
|
414 |
blocking: whether to block while trying to acquire or to operate in
|
415 |
try-lock mode. this locking mode is not supported yet.
|
416 |
|
417 |
Returns:
|
418 |
True: when all the locks are successfully acquired
|
419 |
|
420 |
Raises:
|
421 |
errors.LockError: when any lock we try to acquire has been deleted
|
422 |
before we succeed. In this case none of the locks requested will be
|
423 |
acquired.
|
424 |
|
425 |
"""
|
426 |
if not blocking: |
427 |
# We don't have non-blocking mode for now
|
428 |
raise NotImplementedError |
429 |
|
430 |
# Check we don't already own locks at this level
|
431 |
assert not self._is_owned(), "Cannot acquire locks in the same set twice" |
432 |
|
433 |
if names is None: |
434 |
# If no names are given acquire the whole set by not letting new names
|
435 |
# being added before we release, and getting the current list of names.
|
436 |
# Some of them may then be deleted later, but we'll cope with this.
|
437 |
#
|
438 |
# We'd like to acquire this lock in a shared way, as it's nice if
|
439 |
# everybody else can use the instances at the same time. If are acquiring
|
440 |
# them exclusively though they won't be able to do this anyway, though,
|
441 |
# so we'll get the list lock exclusively as well in order to be able to
|
442 |
# do add() on the set while owning it.
|
443 |
self.__lock.acquire(shared=shared)
|
444 |
try:
|
445 |
# note we own the set-lock
|
446 |
self._add_owned()
|
447 |
names = self.__names()
|
448 |
except:
|
449 |
# We shouldn't have problems adding the lock to the owners list, but
|
450 |
# if we did we'll try to release this lock and re-raise exception.
|
451 |
# Of course something is going to be really wrong, after this.
|
452 |
self.__lock.release()
|
453 |
raise
|
454 |
|
455 |
try:
|
456 |
# Support passing in a single resource to acquire rather than many
|
457 |
if isinstance(names, basestring): |
458 |
names = [names] |
459 |
else:
|
460 |
names.sort() |
461 |
|
462 |
acquire_list = [] |
463 |
# First we look the locks up on __lockdict. We have no way of being sure
|
464 |
# they will still be there after, but this makes it a lot faster should
|
465 |
# just one of them be the already wrong
|
466 |
for lname in utils.UniqueSequence(names): |
467 |
try:
|
468 |
lock = self.__lockdict[lname] # raises KeyError if lock is not there |
469 |
acquire_list.append((lname, lock)) |
470 |
except (KeyError): |
471 |
if self.__lock._is_owned(): |
472 |
# We are acquiring all the set, it doesn't matter if this particular
|
473 |
# element is not there anymore.
|
474 |
continue
|
475 |
else:
|
476 |
raise errors.LockError('non-existing lock in set (%s)' % lname) |
477 |
|
478 |
# This will hold the locknames we effectively acquired.
|
479 |
acquired = set()
|
480 |
# Now acquire_list contains a sorted list of resources and locks we want.
|
481 |
# In order to get them we loop on this (private) list and acquire() them.
|
482 |
# We gave no real guarantee they will still exist till this is done but
|
483 |
# .acquire() itself is safe and will alert us if the lock gets deleted.
|
484 |
for (lname, lock) in acquire_list: |
485 |
try:
|
486 |
lock.acquire(shared=shared) # raises LockError if the lock is deleted
|
487 |
# now the lock cannot be deleted, we have it!
|
488 |
self._add_owned(name=lname)
|
489 |
acquired.add(lname) |
490 |
except (errors.LockError):
|
491 |
if self.__lock._is_owned(): |
492 |
# We are acquiring all the set, it doesn't matter if this particular
|
493 |
# element is not there anymore.
|
494 |
continue
|
495 |
else:
|
496 |
name_fail = lname |
497 |
for lname in self._list_owned(): |
498 |
self.__lockdict[lname].release()
|
499 |
self._del_owned(name=lname)
|
500 |
raise errors.LockError('non-existing lock in set (%s)' % name_fail) |
501 |
except:
|
502 |
# We shouldn't have problems adding the lock to the owners list, but
|
503 |
# if we did we'll try to release this lock and re-raise exception.
|
504 |
# Of course something is going to be really wrong, after this.
|
505 |
if lock._is_owned():
|
506 |
lock.release() |
507 |
raise
|
508 |
|
509 |
except:
|
510 |
# If something went wrong and we had the set-lock let's release it...
|
511 |
if self.__lock._is_owned(): |
512 |
self.__lock.release()
|
513 |
raise
|
514 |
|
515 |
return acquired
|
516 |
|
517 |
def release(self, names=None): |
518 |
"""Release a set of resource locks, at the same level.
|
519 |
|
520 |
You must have acquired the locks, either in shared or in exclusive mode,
|
521 |
before releasing them.
|
522 |
|
523 |
Args:
|
524 |
names: the names of the locks which shall be released.
|
525 |
(defaults to all the locks acquired at that level).
|
526 |
|
527 |
"""
|
528 |
assert self._is_owned(), "release() on lock set while not owner" |
529 |
|
530 |
# Support passing in a single resource to release rather than many
|
531 |
if isinstance(names, basestring): |
532 |
names = [names] |
533 |
|
534 |
if names is None: |
535 |
names = self._list_owned()
|
536 |
else:
|
537 |
names = set(names)
|
538 |
assert self._list_owned().issuperset(names), ( |
539 |
"release() on unheld resources %s" %
|
540 |
names.difference(self._list_owned()))
|
541 |
|
542 |
# First of all let's release the "all elements" lock, if set.
|
543 |
# After this 'add' can work again
|
544 |
if self.__lock._is_owned(): |
545 |
self.__lock.release()
|
546 |
self._del_owned()
|
547 |
|
548 |
for lockname in names: |
549 |
# If we are sure the lock doesn't leave __lockdict without being
|
550 |
# exclusively held we can do this...
|
551 |
self.__lockdict[lockname].release()
|
552 |
self._del_owned(name=lockname)
|
553 |
|
554 |
def add(self, names, acquired=0, shared=0): |
555 |
"""Add a new set of elements to the set
|
556 |
|
557 |
Args:
|
558 |
names: names of the new elements to add
|
559 |
acquired: pre-acquire the new resource?
|
560 |
shared: is the pre-acquisition shared?
|
561 |
|
562 |
"""
|
563 |
# Check we don't already own locks at this level
|
564 |
assert not self._is_owned() or self.__lock._is_owned(shared=0), \ |
565 |
"Cannot add locks if the set is only partially owned, or shared"
|
566 |
|
567 |
# Support passing in a single resource to add rather than many
|
568 |
if isinstance(names, basestring): |
569 |
names = [names] |
570 |
|
571 |
# If we don't already own the set-level lock acquired in an exclusive way
|
572 |
# we'll get it and note we need to release it later.
|
573 |
release_lock = False
|
574 |
if not self.__lock._is_owned(): |
575 |
release_lock = True
|
576 |
self.__lock.acquire()
|
577 |
|
578 |
try:
|
579 |
invalid_names = set(self.__names()).intersection(names) |
580 |
if invalid_names:
|
581 |
# This must be an explicit raise, not an assert, because assert is
|
582 |
# turned off when using optimization, and this can happen because of
|
583 |
# concurrency even if the user doesn't want it.
|
584 |
raise errors.LockError("duplicate add() (%s)" % invalid_names) |
585 |
|
586 |
for lockname in names: |
587 |
lock = SharedLock() |
588 |
|
589 |
if acquired:
|
590 |
lock.acquire(shared=shared) |
591 |
# now the lock cannot be deleted, we have it!
|
592 |
try:
|
593 |
self._add_owned(name=lockname)
|
594 |
except:
|
595 |
# We shouldn't have problems adding the lock to the owners list,
|
596 |
# but if we did we'll try to release this lock and re-raise
|
597 |
# exception. Of course something is going to be really wrong,
|
598 |
# after this. On the other hand the lock hasn't been added to the
|
599 |
# __lockdict yet so no other threads should be pending on it. This
|
600 |
# release is just a safety measure.
|
601 |
lock.release() |
602 |
raise
|
603 |
|
604 |
self.__lockdict[lockname] = lock
|
605 |
|
606 |
finally:
|
607 |
# Only release __lock if we were not holding it previously.
|
608 |
if release_lock:
|
609 |
self.__lock.release()
|
610 |
|
611 |
return True |
612 |
|
613 |
def remove(self, names, blocking=1): |
614 |
"""Remove elements from the lock set.
|
615 |
|
616 |
You can either not hold anything in the lockset or already hold a superset
|
617 |
of the elements you want to delete, exclusively.
|
618 |
|
619 |
Args:
|
620 |
names: names of the resource to remove.
|
621 |
blocking: whether to block while trying to acquire or to operate in
|
622 |
try-lock mode. this locking mode is not supported yet unless
|
623 |
you are already holding exclusively the locks.
|
624 |
|
625 |
Returns:
|
626 |
A list of lock which we removed. The list is always equal to the names
|
627 |
list if we were holding all the locks exclusively.
|
628 |
|
629 |
"""
|
630 |
if not blocking and not self._is_owned(): |
631 |
# We don't have non-blocking mode for now
|
632 |
raise NotImplementedError |
633 |
|
634 |
# Support passing in a single resource to remove rather than many
|
635 |
if isinstance(names, basestring): |
636 |
names = [names] |
637 |
|
638 |
# If we own any subset of this lock it must be a superset of what we want
|
639 |
# to delete. The ownership must also be exclusive, but that will be checked
|
640 |
# by the lock itself.
|
641 |
assert not self._is_owned() or self._list_owned().issuperset(names), ( |
642 |
"remove() on acquired lockset while not owning all elements")
|
643 |
|
644 |
removed = [] |
645 |
|
646 |
for lname in names: |
647 |
# Calling delete() acquires the lock exclusively if we don't already own
|
648 |
# it, and causes all pending and subsequent lock acquires to fail. It's
|
649 |
# fine to call it out of order because delete() also implies release(),
|
650 |
# and the assertion above guarantees that if we either already hold
|
651 |
# everything we want to delete, or we hold none.
|
652 |
try:
|
653 |
self.__lockdict[lname].delete()
|
654 |
removed.append(lname) |
655 |
except (KeyError, errors.LockError): |
656 |
# This cannot happen if we were already holding it, verify:
|
657 |
assert not self._is_owned(), "remove failed while holding lockset" |
658 |
else:
|
659 |
# If no LockError was raised we are the ones who deleted the lock.
|
660 |
# This means we can safely remove it from lockdict, as any further or
|
661 |
# pending delete() or acquire() will fail (and nobody can have the lock
|
662 |
# since before our call to delete()).
|
663 |
#
|
664 |
# This is done in an else clause because if the exception was thrown
|
665 |
# it's the job of the one who actually deleted it.
|
666 |
del self.__lockdict[lname] |
667 |
# And let's remove it from our private list if we owned it.
|
668 |
if self._is_owned(): |
669 |
self._del_owned(name=lname)
|
670 |
|
671 |
return removed
|
672 |
|
673 |
|
674 |
# Locking levels, must be acquired in increasing order.
|
675 |
# Current rules are:
|
676 |
# - at level LEVEL_CLUSTER resides the Big Ganeti Lock (BGL) which must be
|
677 |
# acquired before performing any operation, either in shared or in exclusive
|
678 |
# mode. acquiring the BGL in exclusive mode is discouraged and should be
|
679 |
# avoided.
|
680 |
# - at levels LEVEL_NODE and LEVEL_INSTANCE reside node and instance locks.
|
681 |
# If you need more than one node, or more than one instance, acquire them at
|
682 |
# the same time.
|
683 |
LEVEL_CLUSTER = 0
|
684 |
LEVEL_INSTANCE = 1
|
685 |
LEVEL_NODE = 2
|
686 |
|
687 |
LEVELS = [LEVEL_CLUSTER, |
688 |
LEVEL_INSTANCE, |
689 |
LEVEL_NODE] |
690 |
|
691 |
# Lock levels which are modifiable
|
692 |
LEVELS_MOD = [LEVEL_NODE, LEVEL_INSTANCE] |
693 |
|
694 |
# Constant for the big ganeti lock
|
695 |
BGL = 'BGL'
|
696 |
|
697 |
|
698 |
class GanetiLockManager: |
699 |
"""The Ganeti Locking Library
|
700 |
|
701 |
The purpouse of this small library is to manage locking for ganeti clusters
|
702 |
in a central place, while at the same time doing dynamic checks against
|
703 |
possible deadlocks. It will also make it easier to transition to a different
|
704 |
lock type should we migrate away from python threads.
|
705 |
|
706 |
"""
|
707 |
_instance = None
|
708 |
|
709 |
def __init__(self, nodes=None, instances=None): |
710 |
"""Constructs a new GanetiLockManager object.
|
711 |
|
712 |
There should be only a GanetiLockManager object at any time, so this
|
713 |
function raises an error if this is not the case.
|
714 |
|
715 |
Args:
|
716 |
nodes: list of node names
|
717 |
instances: list of instance names
|
718 |
|
719 |
"""
|
720 |
assert self.__class__._instance is None, "double GanetiLockManager instance" |
721 |
self.__class__._instance = self |
722 |
|
723 |
# The keyring contains all the locks, at their level and in the correct
|
724 |
# locking order.
|
725 |
self.__keyring = {
|
726 |
LEVEL_CLUSTER: LockSet([BGL]), |
727 |
LEVEL_NODE: LockSet(nodes), |
728 |
LEVEL_INSTANCE: LockSet(instances), |
729 |
} |
730 |
|
731 |
def _names(self, level): |
732 |
"""List the lock names at the given level.
|
733 |
Used for debugging/testing purposes.
|
734 |
|
735 |
Args:
|
736 |
level: the level whose list of locks to get
|
737 |
|
738 |
"""
|
739 |
assert level in LEVELS, "Invalid locking level %s" % level |
740 |
return self.__keyring[level]._names() |
741 |
|
742 |
def _is_owned(self, level): |
743 |
"""Check whether we are owning locks at the given level
|
744 |
|
745 |
"""
|
746 |
return self.__keyring[level]._is_owned() |
747 |
|
748 |
is_owned = _is_owned |
749 |
|
750 |
def _list_owned(self, level): |
751 |
"""Get the set of owned locks at the given level
|
752 |
|
753 |
"""
|
754 |
return self.__keyring[level]._list_owned() |
755 |
|
756 |
def _upper_owned(self, level): |
757 |
"""Check that we don't own any lock at a level greater than the given one.
|
758 |
|
759 |
"""
|
760 |
# This way of checking only works if LEVELS[i] = i, which we check for in
|
761 |
# the test cases.
|
762 |
return utils.any((self._is_owned(l) for l in LEVELS[level + 1:])) |
763 |
|
764 |
def _BGL_owned(self): |
765 |
"""Check if the current thread owns the BGL.
|
766 |
|
767 |
Both an exclusive or a shared acquisition work.
|
768 |
|
769 |
"""
|
770 |
return BGL in self.__keyring[LEVEL_CLUSTER]._list_owned() |
771 |
|
772 |
def _contains_BGL(self, level, names): |
773 |
"""Check if acting on the given level and set of names will change the
|
774 |
status of the Big Ganeti Lock.
|
775 |
|
776 |
"""
|
777 |
return level == LEVEL_CLUSTER and (names is None or BGL in names) |
778 |
|
779 |
def acquire(self, level, names, blocking=1, shared=0): |
780 |
"""Acquire a set of resource locks, at the same level.
|
781 |
|
782 |
Args:
|
783 |
level: the level at which the locks shall be acquired.
|
784 |
It must be a memmber of LEVELS.
|
785 |
names: the names of the locks which shall be acquired.
|
786 |
(special lock names, or instance/node names)
|
787 |
shared: whether to acquire in shared mode. By default an exclusive lock
|
788 |
will be acquired.
|
789 |
blocking: whether to block while trying to acquire or to operate in
|
790 |
try-lock mode. this locking mode is not supported yet.
|
791 |
|
792 |
"""
|
793 |
assert level in LEVELS, "Invalid locking level %s" % level |
794 |
|
795 |
# Check that we are either acquiring the Big Ganeti Lock or we already own
|
796 |
# it. Some "legacy" opcodes need to be sure they are run non-concurrently
|
797 |
# so even if we've migrated we need to at least share the BGL to be
|
798 |
# compatible with them. Of course if we own the BGL exclusively there's no
|
799 |
# point in acquiring any other lock, unless perhaps we are half way through
|
800 |
# the migration of the current opcode.
|
801 |
assert (self._contains_BGL(level, names) or self._BGL_owned()), ( |
802 |
"You must own the Big Ganeti Lock before acquiring any other")
|
803 |
|
804 |
# Check we don't own locks at the same or upper levels.
|
805 |
assert not self._upper_owned(level), ("Cannot acquire locks at a level" |
806 |
" while owning some at a greater one")
|
807 |
|
808 |
# Acquire the locks in the set.
|
809 |
return self.__keyring[level].acquire(names, shared=shared, |
810 |
blocking=blocking) |
811 |
|
812 |
def release(self, level, names=None): |
813 |
"""Release a set of resource locks, at the same level.
|
814 |
|
815 |
You must have acquired the locks, either in shared or in exclusive mode,
|
816 |
before releasing them.
|
817 |
|
818 |
Args:
|
819 |
level: the level at which the locks shall be released.
|
820 |
It must be a memmber of LEVELS.
|
821 |
names: the names of the locks which shall be released.
|
822 |
(defaults to all the locks acquired at that level).
|
823 |
|
824 |
"""
|
825 |
assert level in LEVELS, "Invalid locking level %s" % level |
826 |
assert (not self._contains_BGL(level, names) or |
827 |
not self._upper_owned(LEVEL_CLUSTER)), ( |
828 |
"Cannot release the Big Ganeti Lock while holding something"
|
829 |
" at upper levels")
|
830 |
|
831 |
# Release will complain if we don't own the locks already
|
832 |
return self.__keyring[level].release(names) |
833 |
|
834 |
def add(self, level, names, acquired=0, shared=0): |
835 |
"""Add locks at the specified level.
|
836 |
|
837 |
Args:
|
838 |
level: the level at which the locks shall be added.
|
839 |
It must be a memmber of LEVELS_MOD.
|
840 |
names: names of the locks to acquire
|
841 |
acquired: whether to acquire the newly added locks
|
842 |
shared: whether the acquisition will be shared
|
843 |
"""
|
844 |
assert level in LEVELS_MOD, "Invalid or immutable level %s" % level |
845 |
assert self._BGL_owned(), ("You must own the BGL before performing other" |
846 |
" operations")
|
847 |
assert not self._upper_owned(level), ("Cannot add locks at a level" |
848 |
" while owning some at a greater one")
|
849 |
return self.__keyring[level].add(names, acquired=acquired, shared=shared) |
850 |
|
851 |
def remove(self, level, names, blocking=1): |
852 |
"""Remove locks from the specified level.
|
853 |
|
854 |
You must either already own the locks you are trying to remove exclusively
|
855 |
or not own any lock at an upper level.
|
856 |
|
857 |
Args:
|
858 |
level: the level at which the locks shall be removed.
|
859 |
It must be a memmber of LEVELS_MOD.
|
860 |
names: the names of the locks which shall be removed.
|
861 |
(special lock names, or instance/node names)
|
862 |
blocking: whether to block while trying to operate in try-lock mode.
|
863 |
this locking mode is not supported yet.
|
864 |
|
865 |
"""
|
866 |
assert level in LEVELS_MOD, "Invalid or immutable level %s" % level |
867 |
assert self._BGL_owned(), ("You must own the BGL before performing other" |
868 |
" operations")
|
869 |
# Check we either own the level or don't own anything from here up.
|
870 |
# LockSet.remove() will check the case in which we don't own all the needed
|
871 |
# resources, or we have a shared ownership.
|
872 |
assert self._is_owned(level) or not self._upper_owned(level), ( |
873 |
"Cannot remove locks at a level while not owning it or"
|
874 |
" owning some at a greater one")
|
875 |
return self.__keyring[level].remove(names, blocking=blocking) |