onoff/command.py

   1 import logging
   2
   3 from .common import OnoffDevice, OnoffState
   4 from .gobject import spawn_child
   5
   6 logger = logging.getLogger("onoff.command")
   7
   8 class OnoffCommand(OnoffDevice):
   9     """A device that is enabled and disabled by executing separate commands.
  10     The transition period is the duration of the commands.
  11     @type pid: int or None
  12     @ivar pid: is either None or the pid of a transition command as long as
  13             it lives.
  14     @type desired_state: bool
  15     @ivar desired_state: is the state that should be transitioned to
  16     @type target_state: bool
  17     @ivar target_state: is the state that we are currently transitioning to
  18     """
  19     def __init__(self, oncommand, offcommand):
  20         """
  21
  22         @type oncommand: [str]
  23         @param oncommand: an argument vector to be executed for activation.
  24         @type offcommand: [str]
  25         @param offcommand: an argument vector to be executed for deactivation.
  26         @note: For both commands the first element is used as executable and
  27                 looked up in $PATH.
  28         """
  29         OnoffDevice.__init__(self)
  30         self.oncommand = oncommand
  31         self.offcommand = offcommand
  32         self.desired_state = OnoffState.inactive
  33         self.pid = None
  34         self.target_state = OnoffState.inactive  # last command target state
  35
  36     @property
  37     def state(self):
  38         if self.pid is not None:
  39             return self.desired_state | OnoffState.transition
  40         return self.desired_state
  41
  42     def transition(self, state):
  43         command, name = [(self.offcommand, "offcommand"),
  44                          (self.oncommand, "oncommand")][state]
  45         self.target_state = state
  46         logger.info("invoking %s %s", name, " ".join(command))
  47         self.pid = spawn_child(command, self.process_died)
  48         logger.debug("started %s as pid %d", name, self.pid)
  49         self.changestate(self.state)
  50
  51     def process_died(self, pid, condition):
  52         assert self.pid == pid
  53         self.pid = None
  54         logger.info("command %d targeting %s completed", pid,
  55                     self.target_state.name)
  56         if self.desired_state == self.target_state:
  57             self.changestate(self.state)
  58         else:
  59             logger.info("desired state changed to %s during invocation " +
  60                         "targeting %s", self.desired_state.name,
  61                         self.target_state.name)
  62             self.transition(self.desired_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.transition(self.desired_state)
  69
  70     def deactivate(self):
  71         if self.desired_state != OnoffState.inactive:
  72             self.desired_state = OnoffState.inactive
  73             if self.pid is None:
  74                 self.transition(self.desired_state)