Package ganeti :: Module locking :: Class SharedLock
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Class SharedLock

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Implements a shared lock.

Multiple threads can acquire the lock in a shared way by calling acquire(shared=1). In order to acquire the lock in an exclusive way threads can call acquire(shared=0).

Notes on data structures: __pending contains a priority queue (heapq) of all pending acquires: [(priority1: prioqueue1), (priority2: prioqueue2), ...]. Each per-priority queue contains a normal in-order list of conditions to be notified when the lock can be acquired. Shared locks are grouped together by priority and the condition for them is stored in __pending_shared if it already exists. __pending_by_prio keeps references for the per-priority queues indexed by priority for faster access.

Nested Classes [hide private]
  __condition_class
Instance Methods [hide private]
 
__init__(self, name, monitor=None, _time_fn=time.time)
Construct a new SharedLock.
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__repr__(self)
repr(x)
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GetLockInfo(self, requested)
Retrieves information for querying locks.
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__check_deleted(self)
Raises an exception if the lock has been deleted.
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__is_sharer(self)
Is the current thread sharing the lock at this time?
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__is_exclusive(self)
Is the current thread holding the lock exclusively at this time?
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__is_owned(self, shared=-1)
Is the current thread somehow owning the lock at this time?
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is_owned(self, shared=-1)
Is the current thread somehow owning the lock at this time?
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_is_owned(self, shared=-1)
Necessary to remain compatible with threading.Condition, which tries to retrieve a locks' "_is_owned" attribute
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int
_count_pending(self)
Returns the number of pending acquires.
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bool
_check_empty(self)
Checks whether there are any pending acquires.
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__do_acquire(self, shared)
Actually acquire the lock.
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__can_acquire(self, shared)
Determine whether lock can be acquired.
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__find_first_pending_queue(self)
Tries to find the topmost queued entry with pending acquires.
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__is_on_top(self, cond)
Checks whether the passed condition is on top of the queue.
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__acquire_unlocked(self, shared, timeout, priority)
Acquire a shared lock.
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acquire(self, shared=0, timeout=None, priority=None, test_notify=None)
Acquire a shared lock.
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downgrade(self)
Changes the lock mode from exclusive to shared.
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release(self)
Release a Shared Lock.
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__notify_topmost(self)
Notifies topmost condition in queue of pending acquires.
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_notify_topmost(self)
Exported version of __notify_topmost.
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delete(self, timeout=None, priority=None)
Delete a Shared Lock.
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_release_save(self) source code
 
_acquire_restore(self, shared) source code

Inherited from object: __delattr__, __format__, __getattribute__, __hash__, __new__, __reduce__, __reduce_ex__, __setattr__, __sizeof__, __str__, __subclasshook__

Instance Variables [hide private]
string name
the name of the lock
Properties [hide private]

Inherited from object: __class__

Method Details [hide private]

__init__(self, name, monitor=None, _time_fn=time.time)
(Constructor)

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Construct a new SharedLock.

Parameters:
  • name - the name of the lock
  • monitor - Lock monitor with which to register
Overrides: object.__init__

__repr__(self)
(Representation operator)

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repr(x)

Overrides: object.__repr__
(inherited documentation)

GetLockInfo(self, requested)

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Retrieves information for querying locks.

Parameters:
  • requested (set) - Requested information, see query.LQ_*

__is_owned(self, shared=-1)

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Is the current thread somehow owning the lock at this time?

This is a private version of the function, which presumes you're holding the internal lock.

is_owned(self, shared=-1)

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Is the current thread somehow owning the lock at this time?

Parameters:
  • shared -
    • < 0: check for any type of ownership (default)
    • 0: check for exclusive ownership
    • > 0: check for shared ownership

_is_owned(self, shared=-1)

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Necessary to remain compatible with threading.Condition, which tries to retrieve a locks' "_is_owned" attribute

Parameters:
  • shared -
    • < 0: check for any type of ownership (default)
    • 0: check for exclusive ownership
    • > 0: check for shared ownership

__find_first_pending_queue(self)

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Tries to find the topmost queued entry with pending acquires.

Removes empty entries while going through the list.

__is_on_top(self, cond)

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Checks whether the passed condition is on top of the queue.

The caller must make sure the queue isn't empty.

__acquire_unlocked(self, shared, timeout, priority)

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Acquire a shared lock.

Parameters:
  • shared - whether to acquire in shared mode; by default an exclusive lock will be acquired
  • timeout - maximum waiting time before giving up
  • priority (integer) - Priority for acquiring lock

acquire(self, shared=0, timeout=None, priority=None, test_notify=None)

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Acquire a shared lock.

Parameters:
  • shared (integer (0/1) used as a boolean) - whether to acquire in shared mode; by default an exclusive lock will be acquired
  • timeout (float) - maximum waiting time before giving up
  • priority (integer) - Priority for acquiring lock
  • test_notify (callable or None) - Special callback function for unittesting

downgrade(self)

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Changes the lock mode from exclusive to shared.

Pending acquires in shared mode on the same priority will go ahead.

release(self)

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Release a Shared Lock.

You must have acquired the lock, either in shared or in exclusive mode, before calling this function.

delete(self, timeout=None, priority=None)

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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.

Parameters:
  • timeout (float) - maximum waiting time before giving up
  • priority (integer) - Priority for acquiring lock