onoff/process.py

   1 import logging
   2 import os
   3 import signal
   4
   5 from .common import OnoffDevice, OnoffState
   6 from .gobject import spawn_child
   7
   8 logger = logging.getLogger("onoff.process")
   9
  10 class OnoffProcess(OnoffDevice):
  11     """A device that in activated by starting a process and deactivated by
  12     killing the process.
  13
  14     @type pid: int or None
  15     @ivar pid: is either None if there is no process or the pid of the
  16             spawned process
  17     @ivar starting: is either None or a ScheduledFunction representing the
  18             callback signalling the end of the activation transition.
  19     @type killed: bool
  20     @ivar killed: indicates whether the termination signal has been sent
  21             to the spawned process.
  22     """
  23     def __init__(self, command, termsig=signal.SIGTERM):
  24         """
  25         @type command: [str]
  26         @param command: an argument vector to be executed. The first element
  27                 is used as executable and looked up in $PATH.
  28         @param termsig: termination signal to be sent to the process to
  29                 deactivate it. The process must exit in response to this
  30                 signal.
  31         """
  32         OnoffDevice.__init__(self)
  33         self.command = command
  34         self.termsig = termsig
  35         self.desired_state = OnoffState.inactive
  36         self.pid = None
  37         self.killed = False
  38
  39     @property
  40     def state(self):
  41         if self.killed:
  42             return self.desired_state | OnoffState.transition
  43         return self.desired_state
  44
  45     def start_process(self):
  46         assert self.pid is None
  47         logger.info("starting command %s", " ".join(self.command))
  48         self.pid = spawn_child(self.command, self.process_died)
  49         logger.debug("started as pid %d", self.pid)
  50         assert self.desired_state == OnoffState.active
  51         logger.debug("process started")
  52         self.changestate(self.state)
  53
  54     def process_died(self, pid, condition):
  55         assert self.pid == pid
  56         self.pid = None
  57         self.killed = False
  58         logger.info("process %d died", pid)
  59         if self.desired_state == OnoffState.active:
  60             self.start_process()
  61         else:
  62             self.changestate(self.state)
  63
  64     def activate(self):
  65         if self.desired_state != OnoffState.active:
  66             self.desired_state = OnoffState.active
  67             if self.pid is None:
  68                 self.start_process()
  69             else:
  70                 logger.debug("already activated. nothing to do")
  71
  72     def deactivate(self):
  73         if self.desired_state != OnoffState.inactive:
  74             self.desired_state = OnoffState.inactive
  75             if self.pid is not None and not self.killed:
  76                 logger.info("killing process %d", self.pid)
  77                 os.kill(self.pid, self.termsig)
  78                 self.killed = True
  79                 self.changestate(self.state)
  80             else:
  81                 logger.debug("already deactivated. nothing to do.")
  82
  83     def close(self):
  84         self.deactivate()