class FSM(DirectObject): """ A Finite State Machine. This is intended to be the base class of any number of specific machines, which consist of a collection of states and transitions, and rules to switch between states according to arbitrary input data. The states of an FSM are defined implicitly. Each state is identified by a string, which by convention begins with a capital letter. (Also by convention, strings passed to request that are not state names should begin with a lowercase letter.) To define specialized behavior when entering or exiting a particular state, define a method named enterState() and/or exitState(), where "State" is the name of the state, e.g.: def enterRed(self): ... do stuff ... def exitRed(self): ... cleanup stuff ... def enterYellow(self): ... do stuff ... def exitYellow(self): ... cleanup stuff ... def enterGreen(self): ... do stuff ... def exitGreen(self): ... cleanup stuff ... Both functions can access the previous state name as self.oldState, and the new state name we are transitioning to as self.newState. (Of course, in enterRed(), self.newState will always be "Red", and the in exitRed(), self.oldState will always be "Red".) Both functions are optional. If either function is omitted, the state is still defined, but nothing is done when transitioning into (or out of) the state. Additionally, you may define a filterState() function for each state. The purpose of this function is to decide what state to transition to next, if any, on receipt of a particular input. The input is always a string and a tuple of optional parameters (which is often empty), and the return value should either be None to do nothing, or the name of the state to transition into. For example: def filterRed(self, request, args): if request in ['Green']: return (request,) + args return None def filterYellow(self, request, args): if request in ['Red']: return (request,) + args return None def filterGreen(self, request, args): if request in ['Yellow']: return (request,) + args return None As above, the filterState() functions are optional. If any is omitted, the defaultFilter() method is called instead. A standard implementation of defaultFilter() is provided, which may be overridden in a derived class to change the behavior on an unexpected transition. If self.defaultTransitions is left unassigned, then the standard implementation of defaultFilter() will return None for any lowercase transition name and allow any uppercase transition name (this assumes that an uppercase name is a request to go directly to a particular state by name). self.state may be queried at any time other than during the handling of the enter() and exit() functions. During these functions, self.state contains the value None (you are not really in any state during the transition). However, during a transition you *can* query the outgoing and incoming states, respectively, via self.oldState and self.newState. At other times, self.state contains the name of the current state. Initially, the FSM is in state 'Off'. It does not call enterOff() at construction time; it is simply in Off already by convention. If you need to call code in enterOff() to initialize your FSM properly, call it explicitly in the constructor. Similarly, when cleanup() is called or the FSM is destructed, the FSM transitions back to 'Off' by convention. (It does call enterOff() at this point, but does not call exitOff().) To implement nested hierarchical FSM's, simply create a nested FSM and store it on the class within the appropriate enterState() function, and clean it up within the corresponding exitState() function. See the code in SampleFSM.py for further examples. """ notify = DirectNotifyGlobal.directNotify.newCategory("FSM") SerialNum = 0 # This member lists the default transitions that are accepted # without question by the defaultFilter. It's a map of state # names to a list of legal target state names from that state. # Define it only if you want to use the classic FSM model of # defining all (or most) of your transitions up front. If # this is set to None (the default), all named-state # transitions (that is, those requests whose name begins with # a capital letter) are allowed. If it is set to an empty # map, no transitions are implicitly allowed--all transitions # must be approved by some filter function. defaultTransitions = None def __init__(self, name): self.fsmLock = RLock() self.name = name self._serialNum = FSM.SerialNum FSM.SerialNum += 1 self._broadcastStateChanges = False # Initially, we are in the Off state by convention. self.state = 'Off' # This member records transition requests made by demand() or # forceTransition() while the FSM is in transition between # states. self.__requestQueue = [] if __debug__: from panda3d.direct.fsm.ClassicFSM import _debugFsms import weakref _debugFsms[name]=weakref.ref(self) def cleanup(self): # A convenience function to force the FSM to clean itself up # by transitioning to the "Off" state. self.fsmLock.acquire() try: assert self.state if self.state != 'Off': self.__setState('Off') finally: self.fsmLock.release() def setBroadcastStateChanges(self, doBroadcast): self._broadcastStateChanges = doBroadcast def getStateChangeEvent(self): # if setBroadcastStateChanges(True), this event will be sent through # the messenger on every state change. The new and old states are # accessible as self.oldState and self.newState, and the transition # functions will already have been called. return 'FSM-%s-%s-stateChange' % (self._serialNum, self.name) def getCurrentOrNextState(self): # Returns the current state if we are in a state now, or the # state we are transitioning into if we are currently within # the enter or exit function for a state. self.fsmLock.acquire() try: if self.state: return self.state return self.newState finally: self.fsmLock.release() def isInTransition(self): self.fsmLock.acquire() try: return self.state == None finally: self.fsmLock.release() def forceTransition(self, request, *args): """Changes unconditionally to the indicated state. This bypasses the filterState() function, and just calls exitState() followed by enterState().""" self.fsmLock.acquire() try: assert isinstance(request, types.StringTypes) self.notify.debug("%s.forceTransition(%s, %s" % ( self.name, request, str(args)[1:])) if not self.state: # Queue up the request. self.__requestQueue.append(PythonUtil.Functor( self.forceTransition, request, *args)) return self.__setState(request, *args) finally: self.fsmLock.release() def demand(self, request, *args): """Requests a state transition, by code that does not expect the request to be denied. If the request is denied, raises a RequestDenied exception. Unlike request(), this method allows a new request to be made while the FSM is currently in transition. In this case, the request is queued up and will be executed when the current transition finishes. Multiple requests will queue up in sequence. """ self.fsmLock.acquire() try: assert isinstance(request, types.StringTypes) self.notify.debug("%s.demand(%s, %s" % ( self.name, request, str(args)[1:])) if not self.state: # Queue up the request. self.__requestQueue.append(PythonUtil.Functor( self.demand, request, *args)) return if not self.request(request, *args): raise RequestDenied, "%s (from state: %s)" % (request, self.state) finally: self.fsmLock.release() def request(self, request, *args): """Requests a state transition (or other behavior). The request may be denied by the FSM's filter function. If it is denied, the filter function may either raise an exception (RequestDenied), or it may simply return None, without changing the FSM's state. The request parameter should be a string. The request, along with any additional arguments, is passed to the current filterState() function. If filterState() returns a string, the FSM transitions to that state. The return value is the same as the return value of filterState() (that is, None if the request does not provoke a state transition, otherwise it is a tuple containing the name of the state followed by any optional args.) If the FSM is currently in transition (i.e. in the middle of executing an enterState or exitState function), an AlreadyInTransition exception is raised (but see demand(), which will queue these requests up and apply when the transition is complete).""" self.fsmLock.acquire() try: assert isinstance(request, types.StringTypes) self.notify.debug("%s.request(%s, %s" % ( self.name, request, str(args)[1:])) if not self.state: error = "requested %s while FSM is in transition from %s to %s." % (request, self.oldState, self.newState) raise AlreadyInTransition, error func = getattr(self, "filter" + self.state, None) if not func: # If there's no matching filterState() function, call # defaultFilter() instead. func = self.defaultFilter result = func(request, args) if result: if isinstance(result, types.StringTypes): # If the return value is a string, it's just the name # of the state. Wrap it in a tuple for consistency. result = (result,) + args # Otherwise, assume it's a (name, *args) tuple self.__setState(*result) return result finally: self.fsmLock.release() def defaultEnter(self, *args): """ This is the default function that is called if there is no enterState() method for a particular state name. """ pass def defaultExit(self): """ This is the default function that is called if there is no exitState() method for a particular state name. """ pass def defaultFilter(self, request, args): """This is the function that is called if there is no filterState() method for a particular state name. This default filter function behaves in one of two modes: (1) if self.defaultTransitions is None, allow any request whose name begins with a capital letter, which is assumed to be a direct request to a particular state. This is similar to the old ClassicFSM onUndefTransition=ALLOW, with no explicit state transitions listed. (2) if self.defaultTransitions is not None, allow only those requests explicitly identified in this map. This is similar to the old ClassicFSM onUndefTransition=DISALLOW, with an explicit list of allowed state transitions. Specialized FSM's may wish to redefine this default filter (for instance, to always return the request itself, thus allowing any transition.).""" if request == 'Off': # We can always go to the "Off" state. return (request,) + args if self.defaultTransitions is None: # If self.defaultTransitions is None, it means to accept # all requests whose name begins with a capital letter. # These are direct requests to a particular state. if request[0] in string.uppercase: return (request,) + args else: # If self.defaultTransitions is not None, it is a map of # allowed transitions from each state. That is, each key # of the map is the current state name; for that key, the # value is a list of allowed transitions from the # indicated state. if request in self.defaultTransitions.get(self.state, []): # This transition is listed in the defaultTransitions map; # accept it. return (request,) + args # If self.defaultTransitions is not None, it is an error # to request a direct state transition (capital letter # request) not listed in defaultTransitions and not # handled by an earlier filter. if request[0] in string.uppercase: raise RequestDenied, "%s (from state: %s)" % (request, self.state) # In either case, we quietly ignore unhandled command # (lowercase) requests. assert self.notify.debug("%s ignoring request %s from state %s." % (self.name, request, self.state)) return None def filterOff(self, request, args): """From the off state, we can always go directly to any other state.""" if request[0] in string.uppercase: return (request,) + args return self.defaultFilter(request, args) def setStateArray(self, stateArray): """array of unique states to iterate through""" self.fsmLock.acquire() try: self.stateArray = stateArray finally: self.fsmLock.release() def requestNext(self, *args): """request the 'next' state in the predefined state array""" self.fsmLock.acquire() try: assert self.state in self.stateArray curIndex = self.stateArray.index(self.state) newIndex = (curIndex + 1) % len(self.stateArray) self.request(self.stateArray[newIndex], args) finally: self.fsmLock.release() def requestPrev(self, *args): """request the 'previous' state in the predefined state array""" self.fsmLock.acquire() try: assert self.state in self.stateArray curIndex = self.stateArray.index(self.state) newIndex = (curIndex - 1) % len(self.stateArray) self.request(self.stateArray[newIndex], args) finally: self.fsmLock.release() def __setState(self, newState, *args): # Internal function to change unconditionally to the indicated # state. assert self.state assert self.notify.debug("%s to state %s." % (self.name, newState)) self.oldState = self.state self.newState = newState self.state = None try: self.__callExitFunc(self.oldState) self.__callEnterFunc(self.newState, *args) except: # If we got an exception during the enter or exit methods, # go directly to state "InternalError" and raise up the # exception. This might leave things a little unclean # since we've partially transitioned, but what can you do? self.state = 'InternalError' del self.oldState del self.newState raise if self._broadcastStateChanges: messenger.send(self.getStateChangeEvent()) self.state = newState del self.oldState del self.newState if self.__requestQueue: request = self.__requestQueue.pop(0) assert self.notify.debug("%s continued queued request." % (self.name)) request() def __callEnterFunc(self, name, *args): # Calls the appropriate enter function when transitioning into # a new state, if it exists. assert self.state == None and self.newState == name func = getattr(self, "enter" + name, None) if not func: # If there's no matching enterFoo() function, call # defaultEnter() instead. func = self.defaultEnter func(*args) def __callExitFunc(self, name): # Calls the appropriate exit function when leaving a # state, if it exists. assert self.state == None and self.oldState == name func = getattr(self, "exit" + name, None) if not func: # If there's no matching exitFoo() function, call # defaultExit() instead. func = self.defaultExit func() def __repr__(self): return self.__str__() def __str__(self): """ Print out something useful about the fsm """ self.fsmLock.acquire() try: className = self.__class__.__name__ if self.state: str = ('%s FSM:%s in state "%s"' % (className, self.name, self.state)) else: str = ('%s FSM:%s not in any state' % (className, self.name)) return str finally: self.fsmLock.release()