/usr/share/pyshared/sleekxmpp/thirdparty/statemachine.py is in python-sleekxmpp 1.0~beta5-2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 | """
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.lock.acquire(False):
time.sleep(.001)
if (start + wait - time.time()) <= 0.0:
log.debug("Could not acquire lock")
return False
while not self.__current_state in from_states:
# detect timeout:
remainder = start + wait - time.time()
if remainder > 0:
self.notifier.wait(remainder)
else:
log.debug("State was not ready")
self.lock.release()
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()))
|