cmframework/src/cmframework/server/cmeventletrwlock.py

   1 # Copyright 2019 Nokia
   2
   3 # Licensed under the Apache License, Version 2.0 (the "License");
   4 # you may not use this file except in compliance with the License.
   5 # You may obtain a copy of the License at
   6 #
   7 #     http://www.apache.org/licenses/LICENSE-2.0
   8 #
   9 # Unless required by applicable law or agreed to in writing, software
  10 # distributed under the License is distributed on an "AS IS" BASIS,
  11 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  12 # See the License for the specific language governing permissions and
  13 # limitations under the License.
  14 from __future__ import print_function
  15 from eventlet import greenthread, hubs
  16
  17
  18 class CMEventletRWLock(object):
  19     def __init__(self):
  20         self.counter = 0
  21         self._read_waiters = set()
  22         self._write_waiters = set()
  23
  24     def reader(self):
  25         return self.Reader(self)
  26
  27     def writer(self):
  28         return self.Writer(self)
  29
  30     class Base(object):
  31         def __init__(self, parent):
  32             self.parent = parent
  33
  34         def _acquire(self, waiters):
  35             waiters.add(greenthread.getcurrent())
  36
  37             try:
  38                 while self.parent.counter != 0:
  39                     hubs.get_hub().switch()
  40             finally:
  41                 waiters.discard(greenthread.getcurrent())
  42
  43         def _exit(self):
  44             for waiters, fn in (
  45                     (self.parent._read_waiters, lambda x: x >= 0),
  46                     (self.parent._write_waiters, lambda x: x == 0),
  47             ):
  48                 if not waiters:
  49                     continue
  50
  51                 hubs.get_hub().schedule_call_global(
  52                     0, self._release, waiters, fn,
  53                 )
  54
  55         def _release(self, waiters, fn):
  56             if waiters and fn(self.parent.counter):
  57                 waiters.pop().switch()
  58
  59     class Reader(Base):
  60         def __enter__(self):
  61             if self.parent.counter < 0:
  62                 self._acquire(self.parent._read_waiters)
  63             self.parent.counter += 1
  64
  65         def __exit__(self, *args, **kwargs):
  66             self.parent.counter -= 1
  67             self._exit()
  68
  69     class Writer(Base):
  70         def __enter__(self):
  71             if self.parent.counter != 0:
  72                 self._acquire(self.parent._write_waiters)
  73             self.parent.counter -= 1
  74
  75         def __exit__(self, *args, **kwargs):
  76             self.parent.counter += 1
  77             self._exit()
  78
  79
  80 def main():
  81     lock = CMEventletRWLock()
  82     with lock.reader():
  83         print('Got reader lock')
  84
  85     with lock.writer():
  86         print('Got write lock')
  87
  88
  89 if __name__ == '__main__':
  90     main()