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+"""
+ SleekXMPP: The Sleek XMPP Library
+ Copyright (C) 2010 Nathanael C. Fritz
+ This file is part of SleekXMPP.
+
+ See the file LICENSE for copying permission.
+"""
+import threading
+import time
+import logging
+
+log = logging.getLogger(__name__)
+
+
+class StateMachine(object):
+
+ def __init__(self, states=[]):
+ self.lock = threading.Lock()
+ self.notifier = threading.Event()
+ self.__states = []
+ self.addStates(states)
+ self.__default_state = self.__states[0]
+ self.__current_state = self.__default_state
+
+ def addStates(self, states):
+ self.lock.acquire()
+ try:
+ for state in states:
+ if state in self.__states:
+ raise IndexError("The state '%s' is already in the StateMachine." % state)
+ self.__states.append(state)
+ finally: self.lock.release()
+
+
+ def transition(self, from_state, to_state, wait=0.0, func=None, args=[], kwargs={}):
+ '''
+ Transition from the given `from_state` to the given `to_state`.
+ This method will return `True` if the state machine is now in `to_state`. It
+ will return `False` if a timeout occurred the transition did not occur.
+ If `wait` is 0 (the default,) this method returns immediately if the state machine
+ is not in `from_state`.
+
+ If you want the thread to block and transition once the state machine to enters
+ `from_state`, set `wait` to a non-negative value. Note there is no 'block
+ indefinitely' flag since this leads to deadlock. If you want to wait indefinitely,
+ choose a reasonable value for `wait` (e.g. 20 seconds) and do so in a while loop like so:
+
+ ::
+
+ while not thread_should_exit and not state_machine.transition('disconnected', 'connecting', wait=20 ):
+ pass # timeout will occur every 20s unless transition occurs
+ if thread_should_exit: return
+ # perform actions here after successful transition
+
+ This allows the thread to be responsive by setting `thread_should_exit=True`.
+
+ The optional `func` argument allows the user to pass a callable operation which occurs
+ within the context of the state transition (e.g. while the state machine is locked.)
+ If `func` returns a True value, the transition will occur. If `func` returns a non-
+ True value or if an exception is thrown, the transition will not occur. Any thrown
+ exception is not caught by the state machine and is the caller's responsibility to handle.
+ If `func` completes normally, this method will return the value returned by `func.` If
+ values for `args` and `kwargs` are provided, they are expanded and passed like so:
+ `func( *args, **kwargs )`.
+ '''
+
+ return self.transition_any((from_state,), to_state, wait=wait,
+ func=func, args=args, kwargs=kwargs)
+
+
+ def transition_any(self, from_states, to_state, wait=0.0, func=None, args=[], kwargs={}):
+ '''
+ Transition from any of the given `from_states` to the given `to_state`.
+ '''
+
+ if not (isinstance(from_states,tuple) or isinstance(from_states,list)):
+ raise ValueError("from_states should be a list or tuple")
+
+ for state in from_states:
+ if not state in self.__states:
+ raise ValueError("StateMachine does not contain from_state %s." % state)
+ if not to_state in self.__states:
+ raise ValueError("StateMachine does not contain to_state %s." % to_state)
+
+ start = time.time()
+ while not self.lock.acquire(False):
+ time.sleep(.001)
+ if (start + wait - time.time()) <= 0.0:
+ log.debug("Could not acquire lock")
+ return False
+
+ while not self.__current_state in from_states:
+ # detect timeout:
+ remainder = start + wait - time.time()
+ if remainder > 0:
+ self.notifier.wait(remainder)
+ else:
+ log.debug("State was not ready")
+ self.lock.release()
+ return False
+
+ try: # lock is acquired; all other threads will return false or wait until notify/timeout
+ if self.__current_state in from_states: # should always be True due to lock
+
+ # Note that func might throw an exception, but that's OK, it aborts the transition
+ return_val = func(*args,**kwargs) if func is not None else True
+
+ # some 'false' value returned from func,
+ # indicating that transition should not occur:
+ if not return_val: return return_val
+
+ log.debug(' ==== TRANSITION %s -> %s', self.__current_state, to_state)
+ self._set_state(to_state)
+ return return_val # some 'true' value returned by func or True if func was None
+ else:
+ log.error("StateMachine bug!! The lock should ensure this doesn't happen!")
+ return False
+ finally:
+ self.notifier.set() # notify any waiting threads that the state has changed.
+ self.notifier.clear()
+ self.lock.release()
+
+
+ def transition_ctx(self, from_state, to_state, wait=0.0):
+ '''
+ Use the state machine as a context manager. The transition occurs on /exit/ from
+ the `with` context, so long as no exception is thrown. For example:
+
+ ::
+
+ with state_machine.transition_ctx('one','two', wait=5) as locked:
+ if locked:
+ # the state machine is currently locked in state 'one', and will
+ # transition to 'two' when the 'with' statement ends, so long as
+ # no exception is thrown.
+ print 'Currently locked in state one: %s' % state_machine['one']
+
+ else:
+ # The 'wait' timed out, and no lock has been acquired
+ print 'Timed out before entering state "one"'
+
+ print 'Since no exception was thrown, we are now in state "two": %s' % state_machine['two']
+
+
+ The other main difference between this method and `transition()` is that the
+ state machine is locked for the duration of the `with` statement. Normally,
+ after a `transition()` occurs, the state machine is immediately unlocked and
+ available to another thread to call `transition()` again.
+ '''
+
+ if not from_state in self.__states:
+ raise ValueError("StateMachine does not contain from_state %s." % from_state)
+ if not to_state in self.__states:
+ raise ValueError("StateMachine does not contain to_state %s." % to_state)
+
+ return _StateCtx(self, from_state, to_state, wait)
+
+
+ def ensure(self, state, wait=0.0, block_on_transition=False):
+ '''
+ Ensure the state machine is currently in `state`, or wait until it enters `state`.
+ '''
+ return self.ensure_any((state,), wait=wait, block_on_transition=block_on_transition)
+
+
+ def ensure_any(self, states, wait=0.0, block_on_transition=False):
+ '''
+ Ensure we are currently in one of the given `states` or wait until
+ we enter one of those states.
+
+ Note that due to the nature of the function, you cannot guarantee that
+ the entirety of some operation completes while you remain in a given
+ state. That would require acquiring and holding a lock, which
+ would mean no other threads could do the same. (You'd essentially
+ be serializing all of the threads that are 'ensuring' their tasks
+ occurred in some state.
+ '''
+ if not (isinstance(states,tuple) or isinstance(states,list)):
+ raise ValueError('states arg should be a tuple or list')
+
+ for state in states:
+ if not state in self.__states:
+ raise ValueError("StateMachine does not contain state '%s'" % state)
+
+ # if we're in the middle of a transition, determine whether we should
+ # 'fall back' to the 'current' state, or wait for the new state, in order to
+ # avoid an operation occurring in the wrong state.
+ # TODO another option would be an ensure_ctx that uses a semaphore to allow
+ # threads to indicate they want to remain in a particular state.
+
+ # will return immediately if no transition is in process.
+ if block_on_transition:
+ # we're not in the middle of a transition; don't hold the lock
+ if self.lock.acquire(False): self.lock.release()
+ # wait for the transition to complete
+ else: self.notifier.wait()
+
+ start = time.time()
+ while not self.__current_state in states:
+ # detect timeout:
+ remainder = start + wait - time.time()
+ if remainder > 0: self.notifier.wait(remainder)
+ else: return False
+ return True
+
+
+ def reset(self):
+ # TODO need to lock before calling this?
+ self.transition(self.__current_state, self.__default_state)
+
+
+ def _set_state(self, state): #unsynchronized, only call internally after lock is acquired
+ self.__current_state = state
+ return state
+
+
+ def current_state(self):
+ '''
+ Return the current state name.
+ '''
+ return self.__current_state
+
+
+ def __getitem__(self, state):
+ '''
+ Non-blocking, non-synchronized test to determine if we are in the given state.
+ Use `StateMachine.ensure(state)` to wait until the machine enters a certain state.
+ '''
+ return self.__current_state == state
+
+ def __str__(self):
+ return "".join(("StateMachine(", ','.join(self.__states), "): ", self.__current_state))
+
+
+
+class _StateCtx:
+
+ def __init__(self, state_machine, from_state, to_state, wait):
+ self.state_machine = state_machine
+ self.from_state = from_state
+ self.to_state = to_state
+ self.wait = wait
+ self._locked = False
+
+ def __enter__(self):
+ start = time.time()
+ while not self.state_machine[self.from_state] or not self.state_machine.lock.acquire(False):
+ # detect timeout:
+ remainder = start + self.wait - time.time()
+ if remainder > 0: self.state_machine.notifier.wait(remainder)
+ else:
+ log.debug('StateMachine timeout while waiting for state: %s', self.from_state)
+ return False
+
+ self._locked = True # lock has been acquired at this point
+ self.state_machine.notifier.clear()
+ log.debug('StateMachine entered context in state: %s',
+ self.state_machine.current_state())
+ return True
+
+ def __exit__(self, exc_type, exc_val, exc_tb):
+ if exc_val is not None:
+ log.exception("StateMachine exception in context, remaining in state: %s\n%s:%s",
+ self.state_machine.current_state(), exc_type.__name__, exc_val)
+
+ if self._locked:
+ if exc_val is None:
+ log.debug(' ==== TRANSITION %s -> %s',
+ self.state_machine.current_state(), self.to_state)
+ self.state_machine._set_state(self.to_state)
+
+ self.state_machine.notifier.set()
+ self.state_machine.lock.release()
+
+ return False # re-raise any exception
+
+if __name__ == '__main__':
+
+ def callback(s, s2):
+ print((1, s.transition('on', 'off', wait=0.0, func=callback, args=[s,s2])))
+ print((2, s2.transition('off', 'on', func=callback, args=[s,s2])))
+ return True
+
+ s = StateMachine(('off', 'on'))
+ s2 = StateMachine(('off', 'on'))
+ print((3, s.transition('off', 'on', wait=0.0, func=callback, args=[s,s2]),))
+ print((s.current_state(), s2.current_state()))