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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.txt for copying permission.
"""
from __future__ import with_statement
import threading
import time
import logging
class StateMachine(object):
def __init__(self, states=[]):
self.lock = threading.Condition(threading.RLock())
self.__states= []
self.addStates(states)
self.__default_state = self.__states[0]
self.__current_state = self.__default_state
def addStates(self, states):
with self.lock:
for state in states:
if state in self.__states:
raise IndexError("The state '%s' is already in the StateMachine." % state)
self.__states.append( state )
def transition(self, from_state, to_state, wait=0.0):
'''
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 interrupted by setting `thread_should_exit=True`
'''
return self.transition_any( (from_state,), to_state, wait=wait )
def transition_any(self, from_states, to_state, wait=0.0):
'''
Transition from any of the given `from_states` to the given `to_state`.
'''
with self.lock:
for state in from_states:
if isinstance(state,tuple) or isinstance(state,list):
raise ValueError( "State %s should be a string. Did you mean to call 'StateMachine.transition_any()?" % str(state) )
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:
# detect timeout:
if time.time() >= start + wait: return False
self.lock.wait(wait)
if self.__current_state in from_states: # should always be True due to lock
logging.debug(' ==== TRANSITION %s -> %s', self.__current_state, to_state)
self.__current_state = to_state
self.lock.notifyAll()
return True
else:
logging.error( "StateMachine bug!! The lock should ensure this doesn't happen!" )
return False
def ensure(self, state, wait=0.0):
'''
Ensure the state machine is currently in `state`, or wait until it enters `state`.
'''
return self.ensure_any( (state,), wait=wait )
def ensure_any(self, states, wait=0.0):
'''
Ensure we are currently in one of the given `states`
'''
with self.lock:
for state in states:
if isinstance(state,tuple) or isinstance(state,list):
raise ValueError( "State %s should be a string. Did you mean to call 'StateMachine.transition_any()?" % str(state) )
if not state in self.__states:
raise ValueError( "StateMachine does not contain state %s." % state )
start = time.time()
while not self.__current_state in states:
# detect timeout:
if time.time() >= start + wait: return False
self.lock.wait(wait)
return self.__current_state in states # should always be True due to lock
def reset(self):
# TODO need to lock before calling this?
self.transition(self.__current_state, self._default_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 __enter__(self):
self.lock.acquire()
return self
def __exit__(self, exc_type, exc_val, exc_tb):
self.lock.nofityAll()
self.lock.release()
return False # re-raise any exception
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