m_librarian/web/utils.py

   1 from fcntl import flock, LOCK_EX, LOCK_UN, LOCK_NB
   2 from tempfile import gettempdir
   3 import os
   4 import socket
   5
   6
   7 if os.access('/var/run/lock', os.W_OK):
   8     lock_dir = '/var/run/lock'
   9 else:
  10     lock_dir = gettempdir()
  11
  12 if hasattr(os, 'getuid'):
  13     suffix = '-%d' % os.getuid()
  14 else:
  15     suffix = ''
  16
  17 lock_fname = os.path.join(lock_dir, 'm_librarian%s.lock' % suffix)
  18
  19
  20 def get_lock(port):
  21     try:
  22         lock_file = open(lock_fname, 'r')
  23     except IOError:  # no lock file
  24         pass
  25     else:
  26         try:
  27             flock(lock_file, LOCK_EX | LOCK_NB)
  28         except IOError:  # locked
  29             port = int(lock_file.readline())
  30             lock_file.close()
  31             return None, port
  32         else:
  33             flock(lock_file, LOCK_UN)
  34             lock_file.close()
  35
  36     lock_file = open(lock_fname, 'w')
  37     lock_file.write(str(port))
  38     lock_file.close()
  39     lock_file = open(lock_fname, 'r')
  40     flock(lock_file, LOCK_EX | LOCK_NB)
  41     return lock_file, None
  42
  43
  44 def close_lock(lock_file):
  45     flock(lock_file, LOCK_UN)
  46     lock_file.close()
  47     lock_file = open(lock_fname, 'w')
  48     lock_file.write('')
  49     lock_file.close()
  50     os.remove(lock_fname)
  51
  52
  53 def get_open_port():
  54     # https://stackoverflow.com/a/2838309/7976758
  55     s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
  56     s.bind(("", 0))
  57     # s.listen(1)
  58     port = s.getsockname()[1]
  59     s.close()
  60     return port