new state machine in place

1 files changed, 278 insertions, 0 deletions

diff --git a/sleekxmpp/thirdparty/statemachine.py b/sleekxmpp/thirdparty/statemachine.py
new file mode 100644
index 00000000..140c0819
--- /dev/null
+++ b/sleekxmpp/thirdparty/statemachine.py
@@ -0,0 +1,278 @@
+"""
+    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.__current_state in from_states or not self.lock.acquire(False):
+			# detect timeout:
+			remainder = start + wait - time.time()
+			if remainder > 0: self.notifier.wait(remainder)
+			else: 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()