ceph/src/pybind/mgr/volumes/fs/operations/lock.py

   1 from contextlib import contextmanager
   2 from threading import Lock
   3 from typing import Dict
   4
   5 # singleton design pattern taken from http://www.aleax.it/5ep.html
   6
   7 class GlobalLock(object):
   8     """
   9     Global lock to serialize operations in mgr/volumes. This lock
  10     is currently held when accessing (opening) a volume to perform
  11     group/subvolume operations. Since this is a big lock, it's rather
  12     inefficient -- but right now it's ok since mgr/volumes does not
  13     expect concurrent operations via its APIs.
  14
  15     As and when features get added (such as clone, where mgr/volumes
  16     would maintain subvolume states in the filesystem), there might
  17     be a need to allow concurrent operations. In that case it would
  18     be nice to implement an efficient path based locking mechanism.
  19
  20     See: https://people.eecs.berkeley.edu/~kubitron/courses/cs262a-F14/projects/reports/project6_report.pdf
  21     """
  22     _shared_state = {
  23         'lock' : Lock(),
  24         'init' : False
  25     } # type: Dict
  26
  27     def __init__(self):
  28         with self._shared_state['lock']:
  29             if not self._shared_state['init']:
  30                 self._shared_state['init'] = True
  31         # share this state among all instances
  32         self.__dict__ = self._shared_state
  33
  34     @contextmanager
  35     def lock_op(self):
  36         with self._shared_state['lock']:
  37             yield