# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
# 02110-1301, USA.
-"""Module implementing the Ganeti locking code."""
+# Disable "Invalid name ..." message
+# pylint: disable-msg=C0103
-# pylint: disable-msg=W0613,W0201
+"""Module implementing the Ganeti locking code."""
+import os
+import select
import threading
-# Wouldn't it be better to define LockingError in the locking module?
-# Well, for now that's how the rest of the code does it...
+import time
+import errno
+
from ganeti import errors
+from ganeti import utils
+
+
+def ssynchronized(lock, shared=0):
+ """Shared Synchronization decorator.
+
+ Calls the function holding the given lock, either in exclusive or shared
+ mode. It requires the passed lock to be a SharedLock (or support its
+ semantics).
+
+ """
+ def wrap(fn):
+ def sync_function(*args, **kwargs):
+ lock.acquire(shared=shared)
+ try:
+ return fn(*args, **kwargs)
+ finally:
+ lock.release()
+ return sync_function
+ return wrap
+
+
+class _SingleNotifyPipeConditionWaiter(object):
+ """Helper class for SingleNotifyPipeCondition
+
+ """
+ __slots__ = [
+ "_fd",
+ "_poller",
+ ]
+
+ def __init__(self, poller, fd):
+ """Constructor for _SingleNotifyPipeConditionWaiter
+
+ @type poller: select.poll
+ @param poller: Poller object
+ @type fd: int
+ @param fd: File descriptor to wait for
+
+ """
+ object.__init__(self)
+ self._poller = poller
+ self._fd = fd
+
+ def __call__(self, timeout):
+ """Wait for something to happen on the pipe.
+
+ @type timeout: float or None
+ @param timeout: Timeout for waiting (can be None)
+
+ """
+ start_time = time.time()
+ remaining_time = timeout
+
+ while timeout is None or remaining_time > 0:
+ try:
+ result = self._poller.poll(remaining_time)
+ except EnvironmentError, err:
+ if err.errno != errno.EINTR:
+ raise
+ result = None
+
+ # Check whether we were notified
+ if result and result[0][0] == self._fd:
+ break
+
+ # Re-calculate timeout if necessary
+ if timeout is not None:
+ remaining_time = start_time + timeout - time.time()
+
+
+class _BaseCondition(object):
+ """Base class containing common code for conditions.
+
+ Some of this code is taken from python's threading module.
+
+ """
+ __slots__ = [
+ "_lock",
+ "acquire",
+ "release",
+ ]
+
+ def __init__(self, lock):
+ """Constructor for _BaseCondition.
+
+ @type lock: threading.Lock
+ @param lock: condition base lock
+
+ """
+ object.__init__(self)
+
+ # Recursive locks are not supported
+ assert not hasattr(lock, "_acquire_restore")
+ assert not hasattr(lock, "_release_save")
+
+ self._lock = lock
+
+ # Export the lock's acquire() and release() methods
+ self.acquire = lock.acquire
+ self.release = lock.release
+
+ def _is_owned(self):
+ """Check whether lock is owned by current thread.
+
+ """
+ if self._lock.acquire(0):
+ self._lock.release()
+ return False
+
+ return True
+
+ def _check_owned(self):
+ """Raise an exception if the current thread doesn't own the lock.
+
+ """
+ if not self._is_owned():
+ raise RuntimeError("cannot work with un-aquired lock")
+
+
+class SingleNotifyPipeCondition(_BaseCondition):
+ """Condition which can only be notified once.
+
+ This condition class uses pipes and poll, internally, to be able to wait for
+ notification with a timeout, without resorting to polling. It is almost
+ compatible with Python's threading.Condition, with the following differences:
+ - notifyAll can only be called once, and no wait can happen after that
+ - notify is not supported, only notifyAll
+
+ """
+
+ __slots__ = _BaseCondition.__slots__ + [
+ "_poller",
+ "_read_fd",
+ "_write_fd",
+ "_nwaiters",
+ "_notified",
+ ]
+
+ _waiter_class = _SingleNotifyPipeConditionWaiter
+
+ def __init__(self, lock):
+ """Constructor for SingleNotifyPipeCondition
+
+ """
+ _BaseCondition.__init__(self, lock)
+ self._nwaiters = 0
+ self._notified = False
+ self._read_fd = None
+ self._write_fd = None
+ self._poller = None
+
+ def _check_unnotified(self):
+ """Throws an exception if already notified.
+
+ """
+ if self._notified:
+ raise RuntimeError("cannot use already notified condition")
+
+ def _Cleanup(self):
+ """Cleanup open file descriptors, if any.
+
+ """
+ if self._read_fd is not None:
+ os.close(self._read_fd)
+ self._read_fd = None
+
+ if self._write_fd is not None:
+ os.close(self._write_fd)
+ self._write_fd = None
+ self._poller = None
+
+ def wait(self, timeout=None):
+ """Wait for a notification.
+
+ @type timeout: float or None
+ @param timeout: Waiting timeout (can be None)
+
+ """
+ self._check_owned()
+ self._check_unnotified()
+
+ self._nwaiters += 1
+ try:
+ if self._poller is None:
+ (self._read_fd, self._write_fd) = os.pipe()
+ self._poller = select.poll()
+ self._poller.register(self._read_fd, select.POLLHUP)
+ wait_fn = self._waiter_class(self._poller, self._read_fd)
+ self.release()
+ try:
+ # Wait for notification
+ wait_fn(timeout)
+ finally:
+ # Re-acquire lock
+ self.acquire()
+ finally:
+ self._nwaiters -= 1
+ if self._nwaiters == 0:
+ self._Cleanup()
+
+ def notifyAll(self):
+ """Close the writing side of the pipe to notify all waiters.
+
+ """
+ self._check_owned()
+ self._check_unnotified()
+ self._notified = True
+ if self._write_fd is not None:
+ os.close(self._write_fd)
+ self._write_fd = None
+
+
+class PipeCondition(_BaseCondition):
+ """Group-only non-polling condition with counters.
+
+ This condition class uses pipes and poll, internally, to be able to wait for
+ notification with a timeout, without resorting to polling. It is almost
+ compatible with Python's threading.Condition, but only supports notifyAll and
+ non-recursive locks. As an additional features it's able to report whether
+ there are any waiting threads.
+
+ """
+ __slots__ = _BaseCondition.__slots__ + [
+ "_nwaiters",
+ "_single_condition",
+ ]
+
+ _single_condition_class = SingleNotifyPipeCondition
+
+ def __init__(self, lock):
+ """Initializes this class.
+
+ """
+ _BaseCondition.__init__(self, lock)
+ self._nwaiters = 0
+ self._single_condition = self._single_condition_class(self._lock)
+
+ def wait(self, timeout=None):
+ """Wait for a notification.
+
+ @type timeout: float or None
+ @param timeout: Waiting timeout (can be None)
+
+ """
+ self._check_owned()
+
+ # Keep local reference to the pipe. It could be replaced by another thread
+ # notifying while we're waiting.
+ my_condition = self._single_condition
+
+ assert self._nwaiters >= 0
+ self._nwaiters += 1
+ try:
+ my_condition.wait(timeout)
+ finally:
+ assert self._nwaiters > 0
+ self._nwaiters -= 1
+
+ def notifyAll(self):
+ """Notify all currently waiting threads.
+
+ """
+ self._check_owned()
+ self._single_condition.notifyAll()
+ self._single_condition = self._single_condition_class(self._lock)
+
+ def has_waiting(self):
+ """Returns whether there are active waiters.
+
+ """
+ self._check_owned()
+
+ return bool(self._nwaiters)
+
+
+class _CountingCondition(object):
+ """Wrapper for Python's built-in threading.Condition class.
+
+ This wrapper keeps a count of active waiters. We can't access the internal
+ "__waiters" attribute of threading.Condition because it's not thread-safe.
+
+ """
+ __slots__ = [
+ "_cond",
+ "_nwaiters",
+ ]
+
+ def __init__(self, lock):
+ """Initializes this class.
-class SharedLock:
+ """
+ object.__init__(self)
+ self._cond = threading.Condition(lock=lock)
+ self._nwaiters = 0
+
+ def notifyAll(self):
+ """Notifies the condition.
+
+ """
+ return self._cond.notifyAll()
+
+ def wait(self, timeout=None):
+ """Waits for the condition to be notified.
+
+ @type timeout: float or None
+ @param timeout: Waiting timeout (can be None)
+
+ """
+ assert self._nwaiters >= 0
+
+ self._nwaiters += 1
+ try:
+ return self._cond.wait(timeout=timeout)
+ finally:
+ self._nwaiters -= 1
+
+ def has_waiting(self):
+ """Returns whether there are active waiters.
+
+ """
+ return bool(self._nwaiters)
+
+
+class SharedLock(object):
"""Implements a shared lock.
Multiple threads can acquire the lock in a shared way, calling
eventually do so.
"""
+ __slots__ = [
+ "__active_shr_c",
+ "__inactive_shr_c",
+ "__deleted",
+ "__exc",
+ "__lock",
+ "__pending",
+ "__shr",
+ ]
+
+ __condition_class = PipeCondition
+
def __init__(self):
- """Construct a new SharedLock"""
- # we have two conditions, c_shr and c_exc, sharing the same lock.
+ """Construct a new SharedLock.
+
+ """
+ object.__init__(self)
+
+ # Internal lock
self.__lock = threading.Lock()
- self.__turn_shr = threading.Condition(self.__lock)
- self.__turn_exc = threading.Condition(self.__lock)
- # current lock holders
+ # Queue containing waiting acquires
+ self.__pending = []
+
+ # Active and inactive conditions for shared locks
+ self.__active_shr_c = self.__condition_class(self.__lock)
+ self.__inactive_shr_c = self.__condition_class(self.__lock)
+
+ # Current lock holders
self.__shr = set()
self.__exc = None
- # lock waiters
- self.__nwait_exc = 0
- self.__nwait_shr = 0
-
# is this lock in the deleted state?
self.__deleted = False
+ def __check_deleted(self):
+ """Raises an exception if the lock has been deleted.
+
+ """
+ if self.__deleted:
+ raise errors.LockError("Deleted lock")
+
def __is_sharer(self):
- """Is the current thread sharing the lock at this time?"""
+ """Is the current thread sharing the lock at this time?
+
+ """
return threading.currentThread() in self.__shr
def __is_exclusive(self):
- """Is the current thread holding the lock exclusively at this time?"""
+ """Is the current thread holding the lock exclusively at this time?
+
+ """
return threading.currentThread() == self.__exc
def __is_owned(self, shared=-1):
def _is_owned(self, shared=-1):
"""Is the current thread somehow owning the lock at this time?
- Args:
- shared:
- < 0: check for any type of ownership (default)
- 0: check for exclusive ownership
- > 0: check for shared ownership
+ @param shared:
+ - < 0: check for any type of ownership (default)
+ - 0: check for exclusive ownership
+ - > 0: check for shared ownership
+
+ """
+ self.__lock.acquire()
+ try:
+ return self.__is_owned(shared=shared)
+ finally:
+ self.__lock.release()
+
+ def _count_pending(self):
+ """Returns the number of pending acquires.
+
+ @rtype: int
"""
self.__lock.acquire()
try:
- result = self.__is_owned(shared)
+ return len(self.__pending)
finally:
self.__lock.release()
- return result
+ def __do_acquire(self, shared):
+ """Actually acquire the lock.
- def __wait(self,c):
- """Wait on the given condition, and raise an exception if the current lock
- is declared deleted in the meantime.
+ """
+ if shared:
+ self.__shr.add(threading.currentThread())
+ else:
+ self.__exc = threading.currentThread()
- Args:
- c: condition to wait on
+ def __can_acquire(self, shared):
+ """Determine whether lock can be acquired.
"""
- c.wait()
- if self.__deleted:
- raise errors.LockError('deleted lock')
+ if shared:
+ return self.__exc is None
+ else:
+ return len(self.__shr) == 0 and self.__exc is None
- def __exclusive_acquire(self):
- """Acquire the lock exclusively.
+ def __is_on_top(self, cond):
+ """Checks whether the passed condition is on top of the queue.
- This is a private function that presumes you are already holding the
- internal lock. It's defined separately to avoid code duplication between
- acquire() and delete()
+ The caller must make sure the queue isn't empty.
"""
- self.__nwait_exc += 1
- try:
- # This is to save ourselves from a nasty race condition that could
- # theoretically make the sharers starve.
- if self.__nwait_shr > 0 or self.__nwait_exc > 1:
- self.__wait(self.__turn_exc)
+ return self.__pending[0] == cond
- while len(self.__shr) > 0 or self.__exc is not None:
- self.__wait(self.__turn_exc)
+ def __acquire_unlocked(self, shared, timeout):
+ """Acquire a shared lock.
- self.__exc = threading.currentThread()
+ @param shared: whether to acquire in shared mode; by default an
+ exclusive lock will be acquired
+ @param timeout: maximum waiting time before giving up
+
+ """
+ self.__check_deleted()
+
+ # We cannot acquire the lock if we already have it
+ assert not self.__is_owned(), "double acquire() on a non-recursive lock"
+
+ # Check whether someone else holds the lock or there are pending acquires.
+ if not self.__pending and self.__can_acquire(shared):
+ # Apparently not, can acquire lock directly.
+ self.__do_acquire(shared)
+ return True
+
+ if shared:
+ wait_condition = self.__active_shr_c
+
+ # Check if we're not yet in the queue
+ if wait_condition not in self.__pending:
+ self.__pending.append(wait_condition)
+ else:
+ wait_condition = self.__condition_class(self.__lock)
+ # Always add to queue
+ self.__pending.append(wait_condition)
+
+ try:
+ # Wait until we become the topmost acquire in the queue or the timeout
+ # expires.
+ while not (self.__is_on_top(wait_condition) and
+ self.__can_acquire(shared)):
+ # Wait for notification
+ wait_condition.wait(timeout)
+ self.__check_deleted()
+
+ # A lot of code assumes blocking acquires always succeed. Loop
+ # internally for that case.
+ if timeout is not None:
+ break
+
+ if self.__is_on_top(wait_condition) and self.__can_acquire(shared):
+ self.__do_acquire(shared)
+ return True
finally:
- self.__nwait_exc -= 1
+ # Remove condition from queue if there are no more waiters
+ if not wait_condition.has_waiting() and not self.__deleted:
+ self.__pending.remove(wait_condition)
+ return False
- def acquire(self, blocking=1, shared=0):
+ def acquire(self, shared=0, timeout=None, test_notify=None):
"""Acquire a shared lock.
- Args:
- shared: whether to acquire in shared mode. By default an exclusive lock
- will be acquired.
- blocking: whether to block while trying to acquire or to operate in try-lock mode.
- this locking mode is not supported yet.
+ @type shared: int
+ @param shared: whether to acquire in shared mode; by default an
+ exclusive lock will be acquired
+ @type timeout: float
+ @param timeout: maximum waiting time before giving up
+ @type test_notify: callable or None
+ @param test_notify: Special callback function for unittesting
"""
- if not blocking:
- # We don't have non-blocking mode for now
- raise NotImplementedError
-
self.__lock.acquire()
try:
- if self.__deleted:
- raise errors.LockError('deleted lock')
-
- # We cannot acquire the lock if we already have it
- assert not self.__is_owned(), "double acquire() on a non-recursive lock"
-
- if shared:
- self.__nwait_shr += 1
- try:
- # If there is an exclusive holder waiting we have to wait. We'll
- # only do this once, though, when we start waiting for the lock. Then
- # we'll just wait while there are no exclusive holders.
- if self.__nwait_exc > 0:
- # TODO: if !blocking...
- self.__wait(self.__turn_shr)
-
- while self.__exc is not None:
- # TODO: if !blocking...
- self.__wait(self.__turn_shr)
-
- self.__shr.add(threading.currentThread())
- finally:
- self.__nwait_shr -= 1
-
- else:
- # TODO: if !blocking...
- # (or modify __exclusive_acquire for non-blocking mode)
- self.__exclusive_acquire()
+ # We already got the lock, notify now
+ if __debug__ and callable(test_notify):
+ test_notify()
+ return self.__acquire_unlocked(shared, timeout)
finally:
self.__lock.release()
- return True
-
def release(self):
"""Release a Shared Lock.
"""
self.__lock.acquire()
try:
+ assert self.__is_exclusive() or self.__is_sharer(), \
+ "Cannot release non-owned lock"
+
# Autodetect release type
if self.__is_exclusive():
self.__exc = None
-
- # An exclusive holder has just had the lock, time to put it in shared
- # mode if there are shared holders waiting. Otherwise wake up the next
- # exclusive holder.
- if self.__nwait_shr > 0:
- self.__turn_shr.notifyAll()
- elif self.__nwait_exc > 0:
- self.__turn_exc.notify()
-
- elif self.__is_sharer():
+ else:
self.__shr.remove(threading.currentThread())
- # If there are shared holders waiting there *must* be an exclusive holder
- # waiting as well; otherwise what were they waiting for?
- assert (self.__nwait_shr == 0 or self.__nwait_exc > 0,
- "Lock sharers waiting while no exclusive is queueing")
-
- # If there are no more shared holders and some exclusive holders are
- # waiting let's wake one up.
- if len(self.__shr) == 0 and self.__nwait_exc > 0:
- self.__turn_exc.notify()
+ # Notify topmost condition in queue
+ if self.__pending:
+ first_condition = self.__pending[0]
+ first_condition.notifyAll()
- else:
- assert False, "Cannot release non-owned lock"
+ if first_condition == self.__active_shr_c:
+ self.__active_shr_c = self.__inactive_shr_c
+ self.__inactive_shr_c = first_condition
finally:
self.__lock.release()
- def delete(self, blocking=1):
+ def delete(self, timeout=None):
"""Delete a Shared Lock.
This operation will declare the lock for removal. First the lock will be
acquired in exclusive mode if you don't already own it, then the lock
will be put in a state where any future and pending acquire() fail.
- Args:
- blocking: whether to block while trying to acquire or to operate in
- try-lock mode. this locking mode is not supported yet unless
- you are already holding exclusively the lock.
+ @type timeout: float
+ @param timeout: maximum waiting time before giving up
"""
self.__lock.acquire()
try:
- assert not self.__is_sharer(), "cannot delete() a lock while sharing it"
+ assert not self.__is_sharer(), "Cannot delete() a lock while sharing it"
+
+ self.__check_deleted()
+
+ # The caller is allowed to hold the lock exclusively already.
+ acquired = self.__is_exclusive()
+
+ if not acquired:
+ acquired = self.__acquire_unlocked(0, timeout)
- if self.__deleted:
- raise errors.LockError('deleted lock')
+ assert self.__is_exclusive() and not self.__is_sharer(), \
+ "Lock wasn't acquired in exclusive mode"
- if not self.__is_exclusive():
- if not blocking:
- # We don't have non-blocking mode for now
- raise NotImplementedError
- self.__exclusive_acquire()
+ if acquired:
+ self.__deleted = True
+ self.__exc = None
- self.__deleted = True
- self.__exc = None
- # Wake up everybody, they will fail acquiring the lock and
- # raise an exception instead.
- self.__turn_exc.notifyAll()
- self.__turn_shr.notifyAll()
+ # Notify all acquires. They'll throw an error.
+ while self.__pending:
+ self.__pending.pop().notifyAll()
+ return acquired
finally:
self.__lock.release()
+# Whenever we want to acquire a full LockSet we pass None as the value
+# to acquire. Hide this behind this nicely named constant.
+ALL_SET = None
+
+
+class _AcquireTimeout(Exception):
+ """Internal exception to abort an acquire on a timeout.
+
+ """
+
+
class LockSet:
"""Implements a set of locks.
def __init__(self, members=None):
"""Constructs a new LockSet.
- Args:
- members: initial members of the set
+ @param members: initial members of the set
"""
# Used internally to guarantee coherency.
"""Is the current thread a current level owner?"""
return threading.currentThread() in self.__owners
- def _add_owned(self, name):
+ def _add_owned(self, name=None):
"""Note the current thread owns the given lock"""
- if self._is_owned():
- self.__owners[threading.currentThread()].add(name)
+ if name is None:
+ if not self._is_owned():
+ self.__owners[threading.currentThread()] = set()
else:
- self.__owners[threading.currentThread()] = set([name])
+ if self._is_owned():
+ self.__owners[threading.currentThread()].add(name)
+ else:
+ self.__owners[threading.currentThread()] = set([name])
- def _del_owned(self, name):
+ def _del_owned(self, name=None):
"""Note the current thread owns the given lock"""
- self.__owners[threading.currentThread()].remove(name)
- if not self.__owners[threading.currentThread()]:
+ if name is not None:
+ self.__owners[threading.currentThread()].remove(name)
+
+ # Only remove the key if we don't hold the set-lock as well
+ if (not self.__lock._is_owned() and
+ not self.__owners[threading.currentThread()]):
del self.__owners[threading.currentThread()]
def _list_owned(self):
else:
return set()
+ def _release_and_delete_owned(self):
+ """Release and delete all resources owned by the current thread"""
+ for lname in self._list_owned():
+ self.__lockdict[lname].release()
+ self._del_owned(name=lname)
+
def __names(self):
"""Return the current set of names.
result after releasing the lock.
"""
- return set(self.__lockdict.keys())
+ return self.__lockdict.keys()
def _names(self):
"""Return a copy of the current set of elements.
Used only for debugging purposes.
+
"""
- self.__lock.acquire(shared=1)
+ # If we don't already own the set-level lock acquired
+ # we'll get it and note we need to release it later.
+ release_lock = False
+ if not self.__lock._is_owned():
+ release_lock = True
+ self.__lock.acquire(shared=1)
try:
result = self.__names()
finally:
- self.__lock.release()
- return result
+ if release_lock:
+ self.__lock.release()
+ return set(result)
- def acquire(self, names, blocking=1, shared=0):
+ def acquire(self, names, timeout=None, shared=0, test_notify=None):
"""Acquire a set of resource locks.
- Args:
- names: the names of the locks which shall be acquired.
- (special lock names, or instance/node names)
- shared: whether to acquire in shared mode. By default an exclusive lock
- will be acquired.
- blocking: whether to block while trying to acquire or to operate in try-lock mode.
- this locking mode is not supported yet.
+ @param names: the names of the locks which shall be acquired
+ (special lock names, or instance/node names)
+ @param shared: whether to acquire in shared mode; by default an
+ exclusive lock will be acquired
+ @type timeout: float or None
+ @param timeout: Maximum time to acquire all locks
+ @type test_notify: callable or None
+ @param test_notify: Special callback function for unittesting
- Returns:
- True: when all the locks are successfully acquired
+ @return: Set of all locks successfully acquired or None in case of timeout
- Raises:
- errors.LockError: when any lock we try to acquire has been deleted
- before we succeed. In this case none of the locks requested will be
- acquired.
+ @raise errors.LockError: when any lock we try to acquire has
+ been deleted before we succeed. In this case none of the
+ locks requested will be acquired.
"""
- if not blocking:
- # We don't have non-blocking mode for now
- raise NotImplementedError
+ assert timeout is None or timeout >= 0.0
# Check we don't already own locks at this level
assert not self._is_owned(), "Cannot acquire locks in the same set twice"
- # Support passing in a single resource to acquire rather than many
- if isinstance(names, basestring):
- names = [names]
+ # We need to keep track of how long we spent waiting for a lock. The
+ # timeout passed to this function is over all lock acquires.
+ remaining_timeout = timeout
+ if timeout is None:
+ start = None
+ calc_remaining_timeout = lambda: None
else:
- names.sort()
+ start = time.time()
+ calc_remaining_timeout = lambda: (start + timeout) - time.time()
+
+ want_all = names is None
+
+ if want_all:
+ # If no names are given acquire the whole set by not letting new names
+ # being added before we release, and getting the current list of names.
+ # Some of them may then be deleted later, but we'll cope with this.
+ #
+ # We'd like to acquire this lock in a shared way, as it's nice if
+ # everybody else can use the instances at the same time. If are acquiring
+ # them exclusively though they won't be able to do this anyway, though,
+ # so we'll get the list lock exclusively as well in order to be able to
+ # do add() on the set while owning it.
+ self.__lock.acquire(shared=shared, timeout=remaining_timeout)
+ try:
+ # note we own the set-lock
+ self._add_owned()
+ names = self.__names()
+ except:
+ # We shouldn't have problems adding the lock to the owners list, but
+ # if we did we'll try to release this lock and re-raise exception.
+ # Of course something is going to be really wrong, after this.
+ self.__lock.release()
+ raise
+
+ # Re-calculate timeout
+ remaining_timeout = calc_remaining_timeout()
- acquire_list = []
- # First we look the locks up on __lockdict. We have no way of being sure
- # they will still be there after, but this makes it a lot faster should
- # just one of them be the already wrong
try:
- for lname in names:
- lock = self.__lockdict[lname] # raises KeyError if the lock is not there
- acquire_list.append((lname, lock))
- except (KeyError):
- raise errors.LockError('non-existing lock in set (%s)' % lname)
-
- # Now acquire_list contains a sorted list of resources and locks we want.
- # In order to get them we loop on this (private) list and acquire() them.
- # We gave no real guarantee they will still exist till this is done but
- # .acquire() itself is safe and will alert us if the lock gets deleted.
- try:
- for (lname, lock) in acquire_list:
- lock.acquire(shared=shared) # raises LockError if the lock is deleted
- try:
- # now the lock cannot be deleted, we have it!
- self._add_owned(lname)
- except:
- # We shouldn't have problems adding the lock to the owners list, but
- # if we did we'll try to release this lock and re-raise exception.
- # Of course something is going to be really wrong, after this.
- lock.release()
- raise
+ try:
+ # Support passing in a single resource to acquire rather than many
+ if isinstance(names, basestring):
+ names = [names]
+ else:
+ names = sorted(names)
+
+ acquire_list = []
+ # First we look the locks up on __lockdict. We have no way of being sure
+ # they will still be there after, but this makes it a lot faster should
+ # just one of them be the already wrong
+ for lname in utils.UniqueSequence(names):
+ try:
+ lock = self.__lockdict[lname] # raises KeyError if lock is not there
+ acquire_list.append((lname, lock))
+ except KeyError:
+ if want_all:
+ # We are acquiring all the set, it doesn't matter if this
+ # particular element is not there anymore.
+ continue
+ else:
+ raise errors.LockError("Non-existing lock in set (%s)" % lname)
+
+ # This will hold the locknames we effectively acquired.
+ acquired = set()
+
+ # Now acquire_list contains a sorted list of resources and locks we
+ # want. In order to get them we loop on this (private) list and
+ # acquire() them. We gave no real guarantee they will still exist till
+ # this is done but .acquire() itself is safe and will alert us if the
+ # lock gets deleted.
+ for (lname, lock) in acquire_list:
+ if __debug__ and callable(test_notify):
+ test_notify_fn = lambda: test_notify(lname)
+ else:
+ test_notify_fn = None
- except (errors.LockError):
- name_fail = lname
- for lname in self._list_owned():
- self.__lockdict[lname].release()
- self._del_owned(lname)
- raise errors.LockError('non-existing lock in set (%s)' % name_fail)
+ try:
+ if timeout is not None and remaining_timeout < 0:
+ raise _AcquireTimeout()
+
+ # raises LockError if the lock was deleted
+ if not lock.acquire(shared=shared, timeout=remaining_timeout,
+ test_notify=test_notify_fn):
+ # Couldn't get lock or timeout occurred
+ if timeout is None:
+ # This shouldn't happen as SharedLock.acquire(timeout=None) is
+ # blocking.
+ raise errors.LockError("Failed to get lock %s" % lname)
+
+ raise _AcquireTimeout()
+
+ # Re-calculate timeout
+ remaining_timeout = calc_remaining_timeout()
+
+ # now the lock cannot be deleted, we have it!
+ self._add_owned(name=lname)
+ acquired.add(lname)
+
+ except _AcquireTimeout:
+ # Release all acquired locks
+ self._release_and_delete_owned()
+ raise
- return True
+ except errors.LockError:
+ if want_all:
+ # We are acquiring all the set, it doesn't matter if this
+ # particular element is not there anymore.
+ continue
+
+ self._release_and_delete_owned()
+
+ raise errors.LockError("Non-existing lock in set (%s)" % lname)
+
+ except:
+ # We shouldn't have problems adding the lock to the owners list, but
+ # if we did we'll try to release this lock and re-raise exception.
+ # Of course something is going to be really wrong, after this.
+ if lock._is_owned():
+ lock.release()
+ raise
+
+ except:
+ # If something went wrong and we had the set-lock let's release it...
+ if want_all:
+ self.__lock.release()
+ raise
+
+ except _AcquireTimeout:
+ if want_all:
+ self._del_owned()
+
+ return None
+
+ return acquired
def release(self, names=None):
"""Release a set of resource locks, at the same level.
You must have acquired the locks, either in shared or in exclusive mode,
before releasing them.
- Args:
- names: the names of the locks which shall be released.
- (defaults to all the locks acquired at that level).
+ @param names: the names of the locks which shall be released
+ (defaults to all the locks acquired at that level).
"""
-
assert self._is_owned(), "release() on lock set while not owner"
# Support passing in a single resource to release rather than many
"release() on unheld resources %s" %
names.difference(self._list_owned()))
+ # First of all let's release the "all elements" lock, if set.
+ # After this 'add' can work again
+ if self.__lock._is_owned():
+ self.__lock.release()
+ self._del_owned()
+
for lockname in names:
# If we are sure the lock doesn't leave __lockdict without being
# exclusively held we can do this...
self.__lockdict[lockname].release()
- self._del_owned(lockname)
+ self._del_owned(name=lockname)
def add(self, names, acquired=0, shared=0):
"""Add a new set of elements to the set
- Args:
- names: names of the new elements to add
- acquired: pre-acquire the new resource?
- shared: is the pre-acquisition shared?
+ @param names: names of the new elements to add
+ @param acquired: pre-acquire the new resource?
+ @param shared: is the pre-acquisition shared?
"""
+ # Check we don't already own locks at this level
+ assert not self._is_owned() or self.__lock._is_owned(shared=0), \
+ "Cannot add locks if the set is only partially owned, or shared"
+
# Support passing in a single resource to add rather than many
if isinstance(names, basestring):
names = [names]
- # Acquire the internal lock in an exclusive way, so there cannot be a
- # conflicting add()
- self.__lock.acquire()
+ # If we don't already own the set-level lock acquired in an exclusive way
+ # we'll get it and note we need to release it later.
+ release_lock = False
+ if not self.__lock._is_owned():
+ release_lock = True
+ self.__lock.acquire()
+
try:
- invalid_names = self.__names().intersection(names)
+ invalid_names = set(self.__names()).intersection(names)
if invalid_names:
# This must be an explicit raise, not an assert, because assert is
# turned off when using optimization, and this can happen because of
lock.acquire(shared=shared)
# now the lock cannot be deleted, we have it!
try:
- self._add_owned(lockname)
+ self._add_owned(name=lockname)
except:
# We shouldn't have problems adding the lock to the owners list,
# but if we did we'll try to release this lock and re-raise
self.__lockdict[lockname] = lock
finally:
- self.__lock.release()
+ # Only release __lock if we were not holding it previously.
+ if release_lock:
+ self.__lock.release()
return True
- def remove(self, names, blocking=1):
+ def remove(self, names):
"""Remove elements from the lock set.
You can either not hold anything in the lockset or already hold a superset
of the elements you want to delete, exclusively.
- Args:
- names: names of the resource to remove.
- blocking: whether to block while trying to acquire or to operate in
- try-lock mode. this locking mode is not supported yet unless
- you are already holding exclusively the locks.
+ @param names: names of the resource to remove.
- Returns:
- A list of lock which we failed to delete. The list is always empty if we
- were holding all the locks exclusively.
+ @return: a list of locks which we removed; the list is always
+ equal to the names list if we were holding all the locks
+ exclusively
"""
- if not blocking and not self._is_owned():
- # We don't have non-blocking mode for now
- raise NotImplementedError
-
# Support passing in a single resource to remove rather than many
if isinstance(names, basestring):
names = [names]
assert not self._is_owned() or self._list_owned().issuperset(names), (
"remove() on acquired lockset while not owning all elements")
- delete_failed=[]
+ removed = []
for lname in names:
# Calling delete() acquires the lock exclusively if we don't already own
# everything we want to delete, or we hold none.
try:
self.__lockdict[lname].delete()
+ removed.append(lname)
except (KeyError, errors.LockError):
- delete_failed.append(lname)
# This cannot happen if we were already holding it, verify:
assert not self._is_owned(), "remove failed while holding lockset"
else:
del self.__lockdict[lname]
# And let's remove it from our private list if we owned it.
if self._is_owned():
- self._del_owned(lname)
+ self._del_owned(name=lname)
+
+ return removed
+
+
+# Locking levels, must be acquired in increasing order.
+# Current rules are:
+# - at level LEVEL_CLUSTER resides the Big Ganeti Lock (BGL) which must be
+# acquired before performing any operation, either in shared or in exclusive
+# mode. acquiring the BGL in exclusive mode is discouraged and should be
+# avoided.
+# - at levels LEVEL_NODE and LEVEL_INSTANCE reside node and instance locks.
+# If you need more than one node, or more than one instance, acquire them at
+# the same time.
+LEVEL_CLUSTER = 0
+LEVEL_INSTANCE = 1
+LEVEL_NODE = 2
+
+LEVELS = [LEVEL_CLUSTER,
+ LEVEL_INSTANCE,
+ LEVEL_NODE]
+
+# Lock levels which are modifiable
+LEVELS_MOD = [LEVEL_NODE, LEVEL_INSTANCE]
+
+LEVEL_NAMES = {
+ LEVEL_CLUSTER: "cluster",
+ LEVEL_INSTANCE: "instance",
+ LEVEL_NODE: "node",
+ }
+
+# Constant for the big ganeti lock
+BGL = 'BGL'
+
+
+class GanetiLockManager:
+ """The Ganeti Locking Library
+
+ The purpose of this small library is to manage locking for ganeti clusters
+ in a central place, while at the same time doing dynamic checks against
+ possible deadlocks. It will also make it easier to transition to a different
+ lock type should we migrate away from python threads.
+
+ """
+ _instance = None
+
+ def __init__(self, nodes=None, instances=None):
+ """Constructs a new GanetiLockManager object.
+
+ There should be only a GanetiLockManager object at any time, so this
+ function raises an error if this is not the case.
+
+ @param nodes: list of node names
+ @param instances: list of instance names
+
+ """
+ assert self.__class__._instance is None, \
+ "double GanetiLockManager instance"
+
+ self.__class__._instance = self
+
+ # The keyring contains all the locks, at their level and in the correct
+ # locking order.
+ self.__keyring = {
+ LEVEL_CLUSTER: LockSet([BGL]),
+ LEVEL_NODE: LockSet(nodes),
+ LEVEL_INSTANCE: LockSet(instances),
+ }
+
+ def _names(self, level):
+ """List the lock names at the given level.
+
+ This can be used for debugging/testing purposes.
+
+ @param level: the level whose list of locks to get
+
+ """
+ assert level in LEVELS, "Invalid locking level %s" % level
+ return self.__keyring[level]._names()
+
+ def _is_owned(self, level):
+ """Check whether we are owning locks at the given level
+
+ """
+ return self.__keyring[level]._is_owned()
+
+ is_owned = _is_owned
- return delete_failed
+ def _list_owned(self, level):
+ """Get the set of owned locks at the given level
+ """
+ return self.__keyring[level]._list_owned()
+
+ def _upper_owned(self, level):
+ """Check that we don't own any lock at a level greater than the given one.
+
+ """
+ # This way of checking only works if LEVELS[i] = i, which we check for in
+ # the test cases.
+ return utils.any((self._is_owned(l) for l in LEVELS[level + 1:]))
+
+ def _BGL_owned(self):
+ """Check if the current thread owns the BGL.
+
+ Both an exclusive or a shared acquisition work.
+
+ """
+ return BGL in self.__keyring[LEVEL_CLUSTER]._list_owned()
+
+ def _contains_BGL(self, level, names):
+ """Check if the level contains the BGL.
+
+ Check if acting on the given level and set of names will change
+ the status of the Big Ganeti Lock.
+
+ """
+ return level == LEVEL_CLUSTER and (names is None or BGL in names)
+
+ def acquire(self, level, names, timeout=None, shared=0):
+ """Acquire a set of resource locks, at the same level.
+
+ @param level: the level at which the locks shall be acquired;
+ it must be a member of LEVELS.
+ @param names: the names of the locks which shall be acquired
+ (special lock names, or instance/node names)
+ @param shared: whether to acquire in shared mode; by default
+ an exclusive lock will be acquired
+ @type timeout: float
+ @param timeout: Maximum time to acquire all locks
+
+ """
+ assert level in LEVELS, "Invalid locking level %s" % level
+
+ # Check that we are either acquiring the Big Ganeti Lock or we already own
+ # it. Some "legacy" opcodes need to be sure they are run non-concurrently
+ # so even if we've migrated we need to at least share the BGL to be
+ # compatible with them. Of course if we own the BGL exclusively there's no
+ # point in acquiring any other lock, unless perhaps we are half way through
+ # the migration of the current opcode.
+ assert (self._contains_BGL(level, names) or self._BGL_owned()), (
+ "You must own the Big Ganeti Lock before acquiring any other")
+
+ # Check we don't own locks at the same or upper levels.
+ assert not self._upper_owned(level), ("Cannot acquire locks at a level"
+ " while owning some at a greater one")
+
+ # Acquire the locks in the set.
+ return self.__keyring[level].acquire(names, shared=shared, timeout=timeout)
+
+ def release(self, level, names=None):
+ """Release a set of resource locks, at the same level.
+
+ You must have acquired the locks, either in shared or in exclusive
+ mode, before releasing them.
+
+ @param level: the level at which the locks shall be released;
+ it must be a member of LEVELS
+ @param names: the names of the locks which shall be released
+ (defaults to all the locks acquired at that level)
+
+ """
+ assert level in LEVELS, "Invalid locking level %s" % level
+ assert (not self._contains_BGL(level, names) or
+ not self._upper_owned(LEVEL_CLUSTER)), (
+ "Cannot release the Big Ganeti Lock while holding something"
+ " at upper levels")
+
+ # Release will complain if we don't own the locks already
+ return self.__keyring[level].release(names)
+
+ def add(self, level, names, acquired=0, shared=0):
+ """Add locks at the specified level.
+
+ @param level: the level at which the locks shall be added;
+ it must be a member of LEVELS_MOD.
+ @param names: names of the locks to acquire
+ @param acquired: whether to acquire the newly added locks
+ @param shared: whether the acquisition will be shared
+
+ """
+ assert level in LEVELS_MOD, "Invalid or immutable level %s" % level
+ assert self._BGL_owned(), ("You must own the BGL before performing other"
+ " operations")
+ assert not self._upper_owned(level), ("Cannot add locks at a level"
+ " while owning some at a greater one")
+ return self.__keyring[level].add(names, acquired=acquired, shared=shared)
+
+ def remove(self, level, names):
+ """Remove locks from the specified level.
+
+ You must either already own the locks you are trying to remove
+ exclusively or not own any lock at an upper level.
+
+ @param level: the level at which the locks shall be removed;
+ it must be a member of LEVELS_MOD
+ @param names: the names of the locks which shall be removed
+ (special lock names, or instance/node names)
+
+ """
+ assert level in LEVELS_MOD, "Invalid or immutable level %s" % level
+ assert self._BGL_owned(), ("You must own the BGL before performing other"
+ " operations")
+ # Check we either own the level or don't own anything from here
+ # up. LockSet.remove() will check the case in which we don't own
+ # all the needed resources, or we have a shared ownership.
+ assert self._is_owned(level) or not self._upper_owned(level), (
+ "Cannot remove locks at a level while not owning it or"
+ " owning some at a greater one")
+ return self.__keyring[level].remove(names)
projects / ganeti-local / blobdiff