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