m_librarian/web/utils.py

   1 from fcntl import flock, LOCK_EX, LOCK_UN, LOCK_NB
   2 from os import path, remove
   3 import socket
   4
   5
   6 lock_fname = path.join(
   7     path.dirname(path.dirname(path.dirname(__file__))),
   8     'tmp', 'm_librarian.lock')
   9
  10
  11 def get_lock(port):
  12     try:
  13         lock_file = open(lock_fname, 'r')
  14     except IOError:  # no lock file
  15         pass
  16     else:
  17         try:
  18             flock(lock_file, LOCK_EX | LOCK_NB)
  19         except IOError:  # locked
  20             port = int(lock_file.readline())
  21             lock_file.close()
  22             return None, port
  23         else:
  24             flock(lock_file, LOCK_UN)
  25             lock_file.close()
  26
  27     lock_file = open(lock_fname, 'w')
  28     lock_file.write(str(port))
  29     lock_file.close()
  30     lock_file = open(lock_fname, 'r')
  31     flock(lock_file, LOCK_EX | LOCK_NB)
  32     return lock_file, None
  33
  34
  35 def close_lock(lock_file):
  36     flock(lock_file, LOCK_UN)
  37     lock_file.close()
  38     lock_file = open(lock_fname, 'w')
  39     lock_file.write('')
  40     lock_file.close()
  41     remove(lock_fname)
  42
  43
  44 def get_open_port():
  45     # https://stackoverflow.com/a/2838309/7976758
  46     s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
  47     s.bind(("", 0))
  48     # s.listen(1)
  49     port = s.getsockname()[1]
  50     s.close()
  51     return port