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()