The cinder.coordination Module

The cinder.coordination Module

Coordination and locking utilities.

class Coordinator(agent_id=None, prefix='')

Bases: object

Tooz coordination wrapper.

Coordination member id is created from concatenated prefix and agent_id parameters.

Parameters:
  • agent_id (str) – Agent identifier
  • prefix (str) – Used to provide member identifier with a meaningful prefix.
get_lock(name)

Return a Tooz backend lock.

Parameters:name (str) – The lock name that is used to identify it across all nodes.
start()
stop()

Disconnect from coordination backend and stop heartbeat.

synchronized(lock_name, blocking=True, coordinator=<cinder.coordination.Coordinator object>)

Synchronization decorator.

Parameters:
  • lock_name (str) – Lock name.
  • blocking – If True, blocks until the lock is acquired. If False, raises exception when not acquired. Otherwise, the value is used as a timeout value and if lock is not acquired after this number of seconds exception is raised.
  • coordinator – Coordinator class to use when creating lock. Defaults to the global coordinator.
Raises:

tooz.coordination.LockAcquireFailed – if lock is not acquired

Decorating a method like so:

@synchronized('mylock')
def foo(self, *args):
   ...

ensures that only one process will execute the foo method at a time.

Different methods can share the same lock:

@synchronized('mylock')
def foo(self, *args):
   ...

@synchronized('mylock')
def bar(self, *args):
   ...

This way only one of either foo or bar can be executing at a time.

Lock name can be formatted using Python format string syntax:

@synchronized('{f_name}-{vol.id}-{snap[name]}')
def foo(self, vol, snap):
   ...

Available field names are: decorated function parameters and f_name as a decorated function name.

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