def __init__(self,
initialState,
currentState=None,
machineName=None,
instanceName=None,
retryOptions=None,
url=None,
queueName=None,
data=None,
contextTypes=None,
method='GET',
persistentLogging=False,
obj=None,
headers=None):
""" Constructor
@param initialState: a State instance
@param currentState: a State instance
@param machineName: the name of the fsm
@param instanceName: the instance name of the fsm
@param retryOptions: the TaskRetryOptions for the machine
@param url: the url of the fsm
@param queueName: the name of the appengine task queue
@param headers: a dict of X-Fantasm request headers to pass along in Tasks
@param persistentLogging: if True, use persistent _FantasmLog model
@param obj: an object that the FSMContext can operate on
"""
assert queueName
super(FSMContext, self).__init__(data or {})
self.initialState = initialState
self.currentState = currentState
self.currentAction = None
if currentState:
self.currentAction = currentState.exitAction
self.machineName = machineName
self.instanceName = instanceName or self._generateUniqueInstanceName()
self.queueName = queueName
self.retryOptions = retryOptions
self.url = url
self.method = method
self.startingEvent = None
self.startingState = None
self.contextTypes = constants.PARAM_TYPES.copy()
if contextTypes:
self.contextTypes.update(contextTypes)
self.logger = Logger(self,
obj=obj,
persistentLogging=persistentLogging)
self.__obj = obj
self.headers = headers
# the following is monkey-patched from handler.py for 'immediate mode'
from google.appengine.api.taskqueue.taskqueue import Queue
self.Queue = Queue # pylint: disable-msg=C0103
def __init__(self, initialState, currentState=None, machineName=None, instanceName=None,
retryOptions=None, url=None, queueName=None, data=None, contextTypes=None,
method='GET', persistentLogging=False, obj=None, headers=None, globalTaskTarget=None,
useRunOnceSemaphore=True):
""" Constructor
@param initialState: a State instance
@param currentState: a State instance
@param machineName: the name of the fsm
@param instanceName: the instance name of the fsm
@param retryOptions: the TaskRetryOptions for the machine
@param url: the url of the fsm
@param queueName: the name of the appengine task queue
@param headers: a dict of X-Fantasm request headers to pass along in Tasks
@param persistentLogging: if True, use persistent _FantasmLog model
@param obj: an object that the FSMContext can operate on
@param globalTaskTarget: the machine-level target configuration parameter
"""
assert queueName
super(FSMContext, self).__init__(data or {})
self.initialState = initialState
self.currentState = currentState
self.currentAction = None
if currentState:
self.currentAction = currentState.exitAction
self.machineName = machineName
self.instanceName = instanceName or self._generateUniqueInstanceName()
self.queueName = queueName
self.retryOptions = retryOptions
self.url = url
self.method = method
self.startingEvent = None
self.startingState = None
self.contextTypes = constants.PARAM_TYPES.copy()
if contextTypes:
self.contextTypes.update(contextTypes)
self.logger = Logger(self, obj=obj, persistentLogging=persistentLogging)
self.__obj = obj
self.headers = headers
self.globalTaskTarget = globalTaskTarget
self.useRunOnceSemaphore = useRunOnceSemaphore
# the following is monkey-patched from handler.py for 'immediate mode'
from google.appengine.api.taskqueue.taskqueue import Queue
self.Queue = Queue # pylint: disable-msg=C0103
class FSMContext(dict):
""" A finite state machine context instance. """
def __init__(self, initialState, currentState=None, machineName=None, instanceName=None,
retryOptions=None, url=None, queueName=None, data=None, contextTypes=None,
method='GET', persistentLogging=False, obj=None, headers=None):
""" Constructor
@param initialState: a State instance
@param currentState: a State instance
@param machineName: the name of the fsm
@param instanceName: the instance name of the fsm
@param retryOptions: the TaskRetryOptions for the machine
@param url: the url of the fsm
@param queueName: the name of the appengine task queue
@param headers: a dict of X-Fantasm request headers to pass along in Tasks
@param persistentLogging: if True, use persistent _FantasmLog model
@param obj: an object that the FSMContext can operate on
"""
assert queueName
super(FSMContext, self).__init__(data or {})
self.initialState = initialState
self.currentState = currentState
self.currentAction = None
if currentState:
self.currentAction = currentState.exitAction
self.machineName = machineName
self.instanceName = instanceName or self._generateUniqueInstanceName()
self.queueName = queueName
self.retryOptions = retryOptions
self.url = url
self.method = method
self.startingEvent = None
self.startingState = None
self.contextTypes = constants.PARAM_TYPES.copy()
if contextTypes:
self.contextTypes.update(contextTypes)
self.logger = Logger(self, obj=obj, persistentLogging=persistentLogging)
self.__obj = obj
self.headers = headers
# the following is monkey-patched from handler.py for 'immediate mode'
from google.appengine.api.taskqueue.taskqueue import Queue
self.Queue = Queue # pylint: disable-msg=C0103
def _generateUniqueInstanceName(self):
""" Generates a unique instance name for this machine.
@return: a FSMContext instanceName that is (pretty darn likely to be) unique
"""
utcnow = datetime.datetime.utcnow()
dateStr = utcnow.strftime('%Y%m%d%H%M%S')
randomStr = ''.join(random.sample(constants.CHARS_FOR_RANDOM, 6))
return '%s-%s-%s' % (self.machineName, dateStr, randomStr)
def putTypedValue(self, key, value):
""" Sets a value on context[key], but casts the value according to self.contextTypes. """
# cast the value to the appropriate type TODO: should this be in FSMContext?
cast = self.contextTypes[key]
kwargs = {}
if cast is simplejson.loads:
kwargs = {'object_hook': models.decode}
if isinstance(value, list):
value = [cast(v, **kwargs) for v in value]
else:
value = cast(value, **kwargs)
# update the context
self[key] = value
def generateInitializationTask(self, countdown=0, taskName=None):
""" Generates a task for initializing the machine. """
assert self.currentState.name == FSM.PSEUDO_INIT
url = self.buildUrl(self.currentState, FSM.PSEUDO_INIT)
params = self.buildParams(self.currentState, FSM.PSEUDO_INIT)
taskName = taskName or self.getTaskName(FSM.PSEUDO_INIT)
transition = self.currentState.getTransition(FSM.PSEUDO_INIT)
task = Task(name=taskName,
method=self.method,
url=url,
params=params,
countdown=countdown,
headers=self.headers,
retry_options=transition.retryOptions)
return task
def fork(self, data=None):
""" Forks the FSMContext.
When an FSMContext is forked, an identical copy of the finite state machine is generated
that will have the same event dispatched to it as the machine that called .fork(). The data
parameter is useful for allowing each forked instance to operate on a different bit of data.
@param data: an option mapping of data to apply to the forked FSMContext
"""
obj = self.__obj
if obj.get(constants.FORKED_CONTEXTS_PARAM) is None:
obj[constants.FORKED_CONTEXTS_PARAM] = []
forkedContexts = obj.get(constants.FORKED_CONTEXTS_PARAM)
data = copy.copy(data) or {}
data[constants.FORK_PARAM] = len(forkedContexts)
forkedContexts.append(self.clone(updateData=data))
def spawn(self, machineName, contexts, countdown=0, method='POST',
_currentConfig=None, taskName=None):
""" Spawns new machines.
@param machineName the machine to spawn
@param contexts a list of contexts (dictionaries) to spawn the new machine(s) with; multiple contexts will spawn
multiple machines
@param countdown the countdown (in seconds) to wait before spawning machines
@param method the method ('GET' or 'POST') to invoke the machine with (default: POST)
@param _currentConfig test injection for configuration
@param taskName used for idempotency; will become the root of the task name for the actual task queued
"""
# using the current task name as a root to startStateMachine will make this idempotent
taskName = taskName or self.__obj[constants.TASK_NAME_PARAM]
startStateMachine(machineName, contexts, taskName=taskName, method=method, countdown=countdown,
_currentConfig=_currentConfig, headers=self.headers)
def initialize(self):
""" Initializes the FSMContext. Queues a Task (so that we can benefit from auto-retry) to dispatch
an event and take the machine from 'pseudo-init' into the state machine's initial state, as
defined in the fsm.yaml file.
@param data: a dict of initial key, value pairs to stuff into the FSMContext
@return: an event string to dispatch to the FSMContext to put it into the initialState
"""
self[constants.STEPS_PARAM] = 0
task = self.generateInitializationTask()
self.Queue(name=self.queueName).add(task)
_FantasmInstance(key_name=self.instanceName, instanceName=self.instanceName).put()
return FSM.PSEUDO_INIT
def dispatch(self, event, obj):
""" The main entry point to move the machine according to an event.
@param event: a string event to dispatch to the FSMContext
@param obj: an object that the FSMContext can operate on
@return: an event string to dispatch to the FSMContext
"""
self.__obj = self.__obj or obj # hold the obj object for use during this context
# store the starting state and event for the handleEvent() method
self.startingState = self.currentState
self.startingEvent = event
nextEvent = None
try:
nextEvent = self.currentState.dispatch(self, event, obj)
if obj.get(constants.FORKED_CONTEXTS_PARAM):
# pylint: disable-msg=W0212
# - accessing the protected method is fine here, since it is an instance of the same class
tasks = []
for context in obj[constants.FORKED_CONTEXTS_PARAM]:
context[constants.STEPS_PARAM] = int(context.get(constants.STEPS_PARAM, '0')) + 1
task = context.queueDispatch(nextEvent, queue=False)
if task: # fan-in magic
if not task.was_enqueued: # fan-in always queues
tasks.append(task)
try:
if tasks:
transition = self.currentState.getTransition(nextEvent)
_queueTasks(self.Queue, transition.queueName, tasks)
except (TaskAlreadyExistsError, TombstonedTaskError):
# unlike a similar block in self.continutation, this is well off the happy path
self.logger.critical(
'Unable to queue fork Tasks %s as it/they already exists. (Machine %s, State %s)',
[task.name for task in tasks if not task.was_enqueued],
self.machineName,
self.currentState.name)
if nextEvent:
self[constants.STEPS_PARAM] = int(self.get(constants.STEPS_PARAM, '0')) + 1
try:
self.queueDispatch(nextEvent)
except (TaskAlreadyExistsError, TombstonedTaskError):
# unlike a similar block in self.continutation, this is well off the happy path
#
# FIXME: when this happens, it means there was failure shortly after queuing the Task, or
# possibly even with queuing the Task. when this happens there is a chance that
# two states in the machine are executing simultaneously, which is may or may not
# be a good thing, depending on what each state does. gracefully handling this
# exception at least means that this state will terminate.
self.logger.critical('Unable to queue next Task as it already exists. (Machine %s, State %s)',
self.machineName,
self.currentState.name)
else:
# if we're not in a final state, emit a log message
# FIXME - somehow we should avoid this message if we're in the "last" step of a continuation...
if not self.currentState.isFinalState and not obj.get(constants.TERMINATED_PARAM):
self.logger.critical('Non-final state did not emit an event. Machine has terminated in an ' +
'unknown state. (Machine %s, State %s)' %
(self.machineName, self.currentState.name))
# if it is a final state, then dispatch the pseudo-final event to finalize the state machine
elif self.currentState.isFinalState and self.currentState.exitAction:
self[constants.STEPS_PARAM] = int(self.get(constants.STEPS_PARAM, '0')) + 1
self.queueDispatch(FSM.PSEUDO_FINAL)
except Exception:
self.logger.exception("FSMContext.dispatch is handling the following exception:")
self._handleException(event, obj)
return nextEvent
def continuation(self, nextToken):
""" Performs a continuation be re-queueing an FSMContext Task with a slightly modified continuation
token. self.startingState and self.startingEvent are used in the re-queue, so this can be seen as a
'fork' of the current context.
@param nextToken: the next continuation token
"""
assert not self.get(constants.INDEX_PARAM) # fan-out after fan-in is not allowed
step = str(self[constants.STEPS_PARAM]) # needs to be a str key into a json dict
# make a copy and set the currentState to the startingState of this context
context = self.clone()
context.currentState = self.startingState
# update the generation and continuation params
gen = context.get(constants.GEN_PARAM, {})
gen[step] = gen.get(step, 0) + 1
context[constants.GEN_PARAM] = gen
context[constants.CONTINUATION_PARAM] = nextToken
try:
# pylint: disable-msg=W0212
# - accessing the protected method is fine here, since it is an instance of the same class
transition = self.startingState.getTransition(self.startingEvent)
context._queueDispatchNormal(self.startingEvent, queue=True, queueName=transition.queueName,
retryOptions=transition.retryOptions)
except (TaskAlreadyExistsError, TombstonedTaskError):
# this can happen when currentState.dispatch() previously succeeded in queueing the continuation
# Task, but failed with the doAction.execute() call in a _previous_ execution of this Task.
# NOTE: this prevent the dreaded "fork bomb"
self.logger.info('Unable to queue continuation Task as it already exists. (Machine %s, State %s)',
self.machineName,
self.currentState.name)
def queueDispatch(self, nextEvent, queue=True):
""" Queues a .dispatch(nextEvent) call in the appengine Task queue.
@param nextEvent: a string event
@param queue: a boolean indicating whether or not to queue a Task, or leave it to the caller
@return: a taskqueue.Task instance which may or may not have been queued already
"""
assert nextEvent is not None
# self.currentState is already transitioned away from self.startingState
transition = self.currentState.getTransition(nextEvent)
queueName = self.__obj.get(constants.QUEUE_NAME_PARAM) or transition.queueName
if transition.target.isFanIn:
task = self._queueDispatchFanIn(nextEvent, fanInPeriod=transition.target.fanInPeriod,
retryOptions=transition.retryOptions,
queueName=queueName)
else:
task = self._queueDispatchNormal(nextEvent, queue=queue, countdown=transition.countdown,
retryOptions=transition.retryOptions,
queueName=queueName)
return task
def _queueDispatchNormal(self, nextEvent, queue=True, countdown=0, retryOptions=None, queueName=None):
""" Queues a call to .dispatch(nextEvent) in the appengine Task queue.
@param nextEvent: a string event
@param queue: a boolean indicating whether or not to queue a Task, or leave it to the caller
@param countdown: the number of seconds to countdown before the queued task fires
@param retryOptions: the RetryOptions for the task
@param queueName: the queue name to Queue into
@return: a taskqueue.Task instance which may or may not have been queued already
"""
assert nextEvent is not None
assert queueName
url = self.buildUrl(self.currentState, nextEvent)
params = self.buildParams(self.currentState, nextEvent)
taskName = self.getTaskName(nextEvent)
task = Task(name=taskName, method=self.method, url=url, params=params, countdown=countdown,
retry_options=retryOptions, headers=self.headers)
if queue:
self.Queue(name=queueName).add(task)
return task
def _queueDispatchFanIn(self, nextEvent, fanInPeriod=0, retryOptions=None, queueName=None):
""" Queues a call to .dispatch(nextEvent) in the task queue, or saves the context to the
datastore for processing by the queued .dispatch(nextEvent)
@param nextEvent: a string event
@param fanInPeriod: the period of time between fan in Tasks
@param queueName: the queue name to Queue into
@return: a taskqueue.Task instance which may or may not have been queued already
"""
assert nextEvent is not None
assert not self.get(constants.INDEX_PARAM) # fan-in after fan-in is not allowed
assert queueName
# we pop this off here because we do not want the fan-out/continuation param as part of the
# task name, otherwise we loose the fan-in - each fan-in gets one work unit.
self.pop(constants.GEN_PARAM, None)
fork = self.pop(constants.FORK_PARAM, None)
# transfer the fan-in-group into the context (under a fixed value key) so that states beyond
# the fan-in get unique Task names
# FIXME: this will likely change once we formalize what to do post fan-in
transition = self.currentState.getTransition(nextEvent)
if self.get(transition.target.fanInGroup) is not None:
self[constants.FAN_IN_GROUP_PARAM] = self[transition.target.fanInGroup]
taskNameBase = self.getTaskName(nextEvent, fanIn=True)
rwlock = ReadWriteLock(taskNameBase, self)
index = rwlock.currentIndex()
# (***)
#
# grab the lock - memcache.incr()
#
# on Task retry, multiple incr() calls are possible. possible ways to handle:
#
# 1. release the lock in a 'finally' clause, but then risk missing a work
# package because acquiring the read lock will succeed even though the
# work package was not written yet.
#
# 2. allow the lock to get too high. the fan-in logic attempts to wait for
# work packages across multiple-retry attempts, so this seems like the
# best option. we basically trade a bit of latency in fan-in for reliability.
#
rwlock.acquireWriteLock(index, nextEvent=nextEvent)
# insert the work package, which is simply a serialized FSMContext
workIndex = '%s-%d' % (taskNameBase, knuthHash(index))
# on retry, we want to ensure we get the same work index for this task
actualTaskName = self.__obj[constants.TASK_NAME_PARAM]
indexKeyName = 'workIndex-' + '-'.join([str(i) for i in [actualTaskName, fork] if i]) or None
semaphore = RunOnceSemaphore(indexKeyName, self)
# check if the workIndex changed during retry
semaphoreWritten = False
if self.__obj[constants.RETRY_COUNT_PARAM] > 0:
# see comment (A) in self._queueDispatchFanIn(...)
time.sleep(constants.DATASTORE_ASYNCRONOUS_INDEX_WRITE_WAIT_TIME)
payload = semaphore.readRunOnceSemaphore(payload=workIndex, transactional=False)
if payload:
semaphoreWritten = True
if payload != workIndex:
self.logger.info("Work index changed from '%s' to '%s' on retry.", payload, workIndex)
workIndex = payload
# update this here so it gets written down into the work package too
self[constants.INDEX_PARAM] = index
# write down two models, one actual work package, one idempotency package
keyName = '-'.join([str(i) for i in [actualTaskName, fork] if i]) or None
work = _FantasmFanIn(context=self, workIndex=workIndex, key_name=keyName)
# close enough to idempotent, but could still write only one of the entities
# FIXME: could be made faster using a bulk put, but this interface is cleaner
if not semaphoreWritten:
semaphore.writeRunOnceSemaphore(payload=workIndex, transactional=False)
# put the work item
db.put(work)
# (A) now the datastore is asynchronously writing the indices, so the work package may
# not show up in a query for a period of time. there is a corresponding time.sleep()
# in the fan-in of self.mergeJoinDispatch(...)
# release the lock - memcache.decr()
rwlock.releaseWriteLock(index)
try:
# insert a task to run in the future and process a bunch of work packages
now = time.time()
url = self.buildUrl(self.currentState, nextEvent)
params = self.buildParams(self.currentState, nextEvent)
task = Task(name='%s-%d' % (taskNameBase, index),
method=self.method,
url=url,
params=params,
eta=datetime.datetime.utcfromtimestamp(now) + datetime.timedelta(seconds=fanInPeriod),
headers=self.headers,
retry_options=retryOptions)
self.Queue(name=queueName).add(task)
return task
except (TaskAlreadyExistsError, TombstonedTaskError):
pass # Fan-in magic
def mergeJoinDispatch(self, event, obj):
""" Performs a merge join on the pending fan-in dispatches.
@param event: an event that is being merge joined (destination state must be a fan in)
@return: a list (possibly empty) of FSMContext instances
"""
# this assertion comes from _queueDispatchFanIn - we never want fan-out info in a fan-in context
assert not self.get(constants.GEN_PARAM)
assert not self.get(constants.FORK_PARAM)
# the work package index is stored in the url of the Task/FSMContext
index = self.get(constants.INDEX_PARAM)
taskNameBase = self.getTaskName(event, fanIn=True)
# see comment (***) in self._queueDispatchFanIn
#
# in the case of failing to acquire a read lock (due to failed release of write lock)
# we have decided to keep retrying
raiseOnFail = False
if self._getTaskRetryLimit() is not None:
raiseOnFail = (self._getTaskRetryLimit() > self.__obj[constants.RETRY_COUNT_PARAM])
rwlock = ReadWriteLock(taskNameBase, self)
rwlock.acquireReadLock(index, raiseOnFail=raiseOnFail)
# and return the FSMContexts list
class FSMContextList(list):
""" A list that supports .logger.info(), .logger.warning() etc.for fan-in actions """
def __init__(self, context, contexts):
""" setup a self.logger for fan-in actions """
super(FSMContextList, self).__init__(contexts)
self.logger = Logger(context)
self.instanceName = context.instanceName
# see comment (A) in self._queueDispatchFanIn(...)
time.sleep(constants.DATASTORE_ASYNCRONOUS_INDEX_WRITE_WAIT_TIME)
# the following step ensure that fan-in only ever operates one time over a list of data
# the entity is created in State.dispatch(...) _after_ all the actions have executed
# successfully
workIndex = '%s-%d' % (taskNameBase, knuthHash(index))
if obj[constants.RETRY_COUNT_PARAM] > 0:
semaphore = RunOnceSemaphore(workIndex, self)
if semaphore.readRunOnceSemaphore(payload=self.__obj[constants.TASK_NAME_PARAM]):
self.logger.info("Fan-in idempotency guard for workIndex '%s', not processing any work items.",
workIndex)
return FSMContextList(self, []) # don't operate over the data again
# fetch all the work packages in the current group for processing
query = _FantasmFanIn.all() \
.filter('workIndex =', workIndex) \
.order('__key__')
# construct a list of FSMContexts
contexts = [self.clone(replaceData=r.context) for r in query]
return FSMContextList(self, contexts)
def _getTaskRetryLimit(self):
""" Method that returns the maximum number of retries for this particular dispatch
@param obj: an object that the FSMContext can operate on
"""
# get task_retry_limit configuration
try:
transition = self.startingState.getTransition(self.startingEvent)
taskRetryLimit = transition.retryOptions.task_retry_limit
except UnknownEventError:
# can't find the transition, use the machine-level default
taskRetryLimit = self.retryOptions.task_retry_limit
return taskRetryLimit
def _handleException(self, event, obj):
""" Method for child classes to override to handle exceptions.
@param event: a string event
@param obj: an object that the FSMContext can operate on
"""
retryCount = obj.get(constants.RETRY_COUNT_PARAM, 0)
taskRetryLimit = self._getTaskRetryLimit()
if taskRetryLimit and retryCount >= taskRetryLimit:
# need to permanently fail
self.logger.critical('Max-requeues reached. Machine has terminated in an unknown state. ' +
'(Machine %s, State %s, Event %s)',
self.machineName, self.startingState.name, event, exc_info=True)
# re-raise, letting App Engine TaskRetryOptions kill the task
raise
else:
# re-raise the exception
self.logger.warning('Exception occurred processing event. Task will be retried. ' +
'(Machine %s, State %s)',
self.machineName, self.startingState.name, exc_info=True)
# this line really just allows unit tests to work - the request is really dead at this point
self.currentState = self.startingState
raise
def buildUrl(self, state, event):
""" Builds the taskqueue url.
@param state: the State to dispatch to
@param event: the event to dispatch
@return: a url that can be used to build a taskqueue.Task instance to .dispatch(event)
"""
assert state and event
return self.url + '%s/%s/%s/' % (state.name,
event,
state.getTransition(event).target.name)
def buildParams(self, state, event):
""" Builds the taskqueue params.
@param state: the State to dispatch to
@param event: the event to dispatch
@return: a dict suitable to use in constructing a url (GET) or using as params (POST)
"""
assert state and event
params = {constants.STATE_PARAM: state.name,
constants.EVENT_PARAM: event,
constants.INSTANCE_NAME_PARAM: self.instanceName}
for key, value in self.items():
if key not in constants.NON_CONTEXT_PARAMS:
if self.contextTypes.get(key) is simplejson.loads:
value = simplejson.dumps(value, cls=models.Encoder)
if isinstance(value, datetime.datetime):
value = str(int(time.mktime(value.utctimetuple())))
if isinstance(value, dict):
# FIXME: should we issue a warning that they should update fsm.yaml?
value = simplejson.dumps(value, cls=models.Encoder)
if isinstance(value, list) and len(value) == 1:
key = key + '[]' # used to preserve lists of length=1 - see handler.py for inverse
params[key] = value
return params
def getTaskName(self, nextEvent, instanceName=None, fanIn=False):
""" Returns a task name that is unique for a specific dispatch
@param nextEvent: the event to dispatch
@return: a task name that can be used to build a taskqueue.Task instance to .dispatch(nextEvent)
"""
transition = self.currentState.getTransition(nextEvent)
parts = []
parts.append(instanceName or self.instanceName)
if self.get(constants.GEN_PARAM):
for (step, gen) in self[constants.GEN_PARAM].items():
parts.append('continuation-%s-%s' % (step, gen))
if self.get(constants.FORK_PARAM):
parts.append('fork-' + str(self[constants.FORK_PARAM]))
# post-fan-in we need to store the workIndex in the task name to avoid duplicates, since
# we popped the generation off during fan-in
# FIXME: maybe not pop the generation in fan-in?
# FIXME: maybe store this in the instanceName?
# FIXME: i wish this was easier to get right :-)
if (not fanIn) and self.get(constants.INDEX_PARAM):
parts.append('work-index-' + str(self[constants.INDEX_PARAM]))
parts.append(self.currentState.name)
parts.append(nextEvent)
parts.append(transition.target.name)
parts.append('step-' + str(self[constants.STEPS_PARAM]))
if self.get(constants.FAN_IN_GROUP_PARAM) is not None:
parts.append('group-' + str(self[constants.FAN_IN_GROUP_PARAM]))
return '--'.join(parts)
def clone(self, instanceName=None, updateData=None, replaceData=None):
""" Returns a copy of the FSMContext.
@param instanceName: the instance name to optionally apply to the clone
@param updateData: a dict/mapping of data to optionally apply (.update()) to the clone
@param replaceData: a dict/mapping of data to optionally apply (.clear()/.update()) to the clone
@return: a new FSMContext instance
"""
assert (not updateData) or (not replaceData), "cannot update and replace data at the same time"
context = copy.deepcopy(self)
if instanceName:
context.instanceName = instanceName
if updateData:
context.update(updateData)
if replaceData:
context.clear()
context.update(replaceData)
return context
class FSMContext(dict):
""" A finite state machine context instance. """
def __init__(self, initialState, currentState=None, machineName=None, instanceName=None,
retryOptions=None, url=None, queueName=None, data=None, contextTypes=None,
method='GET', persistentLogging=False, obj=None, headers=None, globalTaskTarget=None,
useRunOnceSemaphore=True):
""" Constructor
@param initialState: a State instance
@param currentState: a State instance
@param machineName: the name of the fsm
@param instanceName: the instance name of the fsm
@param retryOptions: the TaskRetryOptions for the machine
@param url: the url of the fsm
@param queueName: the name of the appengine task queue
@param headers: a dict of X-Fantasm request headers to pass along in Tasks
@param persistentLogging: if True, use persistent _FantasmLog model
@param obj: an object that the FSMContext can operate on
@param globalTaskTarget: the machine-level target configuration parameter
"""
assert queueName
super(FSMContext, self).__init__(data or {})
self.initialState = initialState
self.currentState = currentState
self.currentAction = None
if currentState:
self.currentAction = currentState.exitAction
self.machineName = machineName
self.instanceName = instanceName or self._generateUniqueInstanceName()
self.queueName = queueName
self.retryOptions = retryOptions
self.url = url
self.method = method
self.startingEvent = None
self.startingState = None
self.contextTypes = constants.PARAM_TYPES.copy()
if contextTypes:
self.contextTypes.update(contextTypes)
self.logger = Logger(self, obj=obj, persistentLogging=persistentLogging)
self.__obj = obj
self.headers = headers
self.globalTaskTarget = globalTaskTarget
self.useRunOnceSemaphore = useRunOnceSemaphore
# the following is monkey-patched from handler.py for 'immediate mode'
from google.appengine.api.taskqueue.taskqueue import Queue
self.Queue = Queue # pylint: disable-msg=C0103
INSTANCE_NAME_DTFORMAT = '%Y%m%d%H%M%S'
def _generateUniqueInstanceName(self):
""" Generates a unique instance name for this machine.
@return: a FSMContext instanceName that is (pretty darn likely to be) unique
"""
utcnow = datetime.datetime.utcnow()
dateStr = utcnow.strftime(self.INSTANCE_NAME_DTFORMAT)
randomStr = ''.join(random.sample(constants.CHARS_FOR_RANDOM, 6))
# note this construction is important for getInstanceStartTime()
return '%s-%s-%s' % (self.machineName, dateStr, randomStr)
def getInstanceStartTime(self):
""" Returns the UTC datetime when the instance was started.
@return a UTC datetime representing when the instance was started.
"""
startDatetimeString = self.instanceName.rsplit('-')[-2]
startDatetime = datetime.datetime.strptime(startDatetimeString, self.INSTANCE_NAME_DTFORMAT)
return startDatetime
def putTypedValue(self, key, value):
""" Sets a value on context[key], but casts the value according to self.contextTypes. """
# cast the value to the appropriate type TODO: should this be in FSMContext?
cast = self.contextTypes[key]
kwargs = {}
if cast is json.loads:
kwargs = {'object_hook': models.decode}
if cast is pickle.loads:
value = pickle.loads(str(value))
elif isinstance(value, list):
value = [cast(v, **kwargs) for v in value]
else:
value = cast(value, **kwargs)
# update the context
self[key] = value
def generateInitializationTask(self, countdown=0, taskName=None, transactional=False):
""" Generates a task for initializing the machine. """
assert self.currentState.name == FSM.PSEUDO_INIT
url = self.buildUrl(self.currentState, FSM.PSEUDO_INIT)
params = self.buildParams(self.currentState, FSM.PSEUDO_INIT)
if transactional:
taskName = None
else:
taskName = taskName or self.getTaskName(FSM.PSEUDO_INIT)
transition = self.currentState.getTransition(FSM.PSEUDO_INIT)
task = Task(name=taskName,
method=self.method,
url=url,
params=params,
countdown=countdown,
headers=self.headers,
retry_options=transition.retryOptions,
target=self.globalTaskTarget)
return task
def fork(self, data=None):
""" Forks the FSMContext.
When an FSMContext is forked, an identical copy of the finite state machine is generated
that will have the same event dispatched to it as the machine that called .fork(). The data
parameter is useful for allowing each forked instance to operate on a different bit of data.
@param data: an option mapping of data to apply to the forked FSMContext
"""
obj = self.__obj
if obj.get(constants.FORKED_CONTEXTS_PARAM) is None:
obj[constants.FORKED_CONTEXTS_PARAM] = []
forkedContexts = obj.get(constants.FORKED_CONTEXTS_PARAM)
data = copy.copy(data) or {}
data[constants.FORK_PARAM] = len(forkedContexts)
forkedContexts.append(self.clone(updateData=data))
def spawn(self, machineName, contexts, countdown=0, method='POST',
_currentConfig=None, taskName=None):
""" Spawns new machines.
@param machineName the machine to spawn
@param contexts a list of contexts (dictionaries) to spawn the new machine(s) with; multiple contexts will spawn
multiple machines
@param countdown the countdown (in seconds) to wait before spawning machines
@param method the method ('GET' or 'POST') to invoke the machine with (default: POST)
@param _currentConfig test injection for configuration
@param taskName used for idempotency; will become the root of the task name for the actual task queued
"""
# using the current task name as a root to startStateMachine will make this idempotent
taskName = taskName or self.__obj[constants.TASK_NAME_PARAM]
startStateMachine(machineName, contexts, taskName=taskName, method=method, countdown=countdown,
_currentConfig=_currentConfig, headers=self.headers)
def initialize(self):
""" Initializes the FSMContext. Queues a Task (so that we can benefit from auto-retry) to dispatch
an event and take the machine from 'pseudo-init' into the state machine's initial state, as
defined in the fsm.yaml file.
@param data: a dict of initial key, value pairs to stuff into the FSMContext
@return: an event string to dispatch to the FSMContext to put it into the initialState
"""
self[constants.STEPS_PARAM] = 0
task = self.generateInitializationTask()
self.Queue(name=self.queueName).add(task)
key = db.Key.from_path(_FantasmInstance.kind(), self.instanceName, namespace='')
_FantasmInstance(key=key, instanceName=self.instanceName).put()
return FSM.PSEUDO_INIT
def dispatch(self, event, obj):
""" The main entry point to move the machine according to an event.
@param event: a string event to dispatch to the FSMContext
@param obj: an object that the FSMContext can operate on
@return: an event string to dispatch to the FSMContext
"""
self.__obj = self.__obj or obj # hold the obj object for use during this context
# store the starting state and event for the handleEvent() method
self.startingState = self.currentState
self.startingEvent = event
nextEvent = None
try:
nextEvent = self.currentState.dispatch(self, event, obj)
if obj.get(constants.FORKED_CONTEXTS_PARAM):
# pylint: disable-msg=W0212
# - accessing the protected method is fine here, since it is an instance of the same class
tasks = []
for context in obj[constants.FORKED_CONTEXTS_PARAM]:
context[constants.STEPS_PARAM] = int(context.get(constants.STEPS_PARAM, '0')) + 1
task = context.queueDispatch(nextEvent, queue=False)
if task: # fan-in magic
if not task.was_enqueued: # fan-in always queues
tasks.append(task)
try:
if tasks:
transition = self.currentState.getTransition(nextEvent)
_queueTasks(self.Queue, transition.queueName, tasks)
except (TaskAlreadyExistsError, TombstonedTaskError):
# unlike a similar block in self.continutation, this is well off the happy path
self.logger.critical(
'Unable to queue fork Tasks %s as it/they already exists. (Machine %s, State %s)',
[task.name for task in tasks if not task.was_enqueued],
self.machineName,
self.currentState.name)
if nextEvent:
self[constants.STEPS_PARAM] = int(self.get(constants.STEPS_PARAM, '0')) + 1
try:
self.queueDispatch(nextEvent)
except (TaskAlreadyExistsError, TombstonedTaskError):
# unlike a similar block in self.continutation, this is well off the happy path
#
# FIXME: when this happens, it means there was failure shortly after queuing the Task, or
# possibly even with queuing the Task. when this happens there is a chance that
# two states in the machine are executing simultaneously, which is may or may not
# be a good thing, depending on what each state does. gracefully handling this
# exception at least means that this state will terminate.
# NOTE: This happens most often due to oddities in the Task Queue system. E.g., task
# queue will raise an exception while doing a BulkAdd or a TransientError occurs,
# however despite this error, the task was enqueued (and the task name was
# registered in the tombstone system). That is, it seems that most often, the
# error that leads to this message does not mean that a particular machine did
# not continue; it probably always does continue. However, not that the particular
# state that issues this particular warning was triggered twice, so any side-effect
# (e.g., sending an email) would have occurred twice. Remember it is very important
# for your machine states to be idemopotent meaning they have to protect against
# this situation on their own as the task queue system itself is distributed and
# definitely not perfect.
self.logger.warning('Unable to queue next Task as it already exists. (Machine %s, State %s)',
self.machineName,
self.currentState.name)
else:
# if we're not in a final state, emit a log message
# FIXME - somehow we should avoid this message if we're in the "last" step of a continuation...
if not self.currentState.isFinalState and not obj.get(constants.TERMINATED_PARAM):
self.logger.critical('Non-final state did not emit an event. Machine has terminated in an ' +
'unknown state. (Machine %s, State %s)' %
(self.machineName, self.currentState.name))
# if it is a final state, then dispatch the pseudo-final event to finalize the state machine
elif self.currentState.isFinalState and self.currentState.exitAction:
self[constants.STEPS_PARAM] = int(self.get(constants.STEPS_PARAM, '0')) + 1
self.queueDispatch(FSM.PSEUDO_FINAL)
except HaltMachineError, e:
if e.level is not None and e.message:
self.logger.log(e.level, e.message)
return None # stop the machine
except Exception, e:
level = self.logger.error
if e.__class__ in TRANSIENT_ERRORS:
level = self.logger.warn
level("FSMContext.dispatch is handling the following exception:", exc_info=True)
self._handleException(event, obj)
def __init__(self, context, contexts):
""" setup a self.logger for fan-in actions """
super(FSMContextList, self).__init__(contexts)
self.logger = Logger(context)
self.instanceName = context.instanceName
class FSMContext(dict):
""" A finite state machine context instance. """
def __init__(self,
initialState,
currentState=None,
machineName=None,
instanceName=None,
retryOptions=None,
url=None,
queueName=None,
data=None,
contextTypes=None,
method='GET',
persistentLogging=False,
obj=None,
headers=None):
""" Constructor
@param initialState: a State instance
@param currentState: a State instance
@param machineName: the name of the fsm
@param instanceName: the instance name of the fsm
@param retryOptions: the TaskRetryOptions for the machine
@param url: the url of the fsm
@param queueName: the name of the appengine task queue
@param headers: a dict of X-Fantasm request headers to pass along in Tasks
@param persistentLogging: if True, use persistent _FantasmLog model
@param obj: an object that the FSMContext can operate on
"""
assert queueName
super(FSMContext, self).__init__(data or {})
self.initialState = initialState
self.currentState = currentState
self.currentAction = None
if currentState:
self.currentAction = currentState.exitAction
self.machineName = machineName
self.instanceName = instanceName or self._generateUniqueInstanceName()
self.queueName = queueName
self.retryOptions = retryOptions
self.url = url
self.method = method
self.startingEvent = None
self.startingState = None
self.contextTypes = constants.PARAM_TYPES.copy()
if contextTypes:
self.contextTypes.update(contextTypes)
self.logger = Logger(self,
obj=obj,
persistentLogging=persistentLogging)
self.__obj = obj
self.headers = headers
# the following is monkey-patched from handler.py for 'immediate mode'
from google.appengine.api.taskqueue.taskqueue import Queue
self.Queue = Queue # pylint: disable-msg=C0103
def _generateUniqueInstanceName(self):
""" Generates a unique instance name for this machine.
@return: a FSMContext instanceName that is (pretty darn likely to be) unique
"""
utcnow = datetime.datetime.utcnow()
dateStr = utcnow.strftime('%Y%m%d%H%M%S')
randomStr = ''.join(random.sample(constants.CHARS_FOR_RANDOM, 6))
return '%s-%s-%s' % (self.machineName, dateStr, randomStr)
def putTypedValue(self, key, value):
""" Sets a value on context[key], but casts the value according to self.contextTypes. """
# cast the value to the appropriate type TODO: should this be in FSMContext?
cast = self.contextTypes[key]
kwargs = {}
if cast is simplejson.loads:
kwargs = {'object_hook': models.decode}
if isinstance(value, list):
value = [cast(v, **kwargs) for v in value]
else:
value = cast(value, **kwargs)
# update the context
self[key] = value
def generateInitializationTask(self, countdown=0, taskName=None):
""" Generates a task for initializing the machine. """
assert self.currentState.name == FSM.PSEUDO_INIT
url = self.buildUrl(self.currentState, FSM.PSEUDO_INIT)
params = self.buildParams(self.currentState, FSM.PSEUDO_INIT)
taskName = taskName or self.getTaskName(FSM.PSEUDO_INIT)
transition = self.currentState.getTransition(FSM.PSEUDO_INIT)
task = Task(name=taskName,
method=self.method,
url=url,
params=params,
countdown=countdown,
headers=self.headers,
retry_options=transition.retryOptions)
return task
def fork(self, data=None):
""" Forks the FSMContext.
When an FSMContext is forked, an identical copy of the finite state machine is generated
that will have the same event dispatched to it as the machine that called .fork(). The data
parameter is useful for allowing each forked instance to operate on a different bit of data.
@param data: an option mapping of data to apply to the forked FSMContext
"""
obj = self.__obj
if obj.get(constants.FORKED_CONTEXTS_PARAM) is None:
obj[constants.FORKED_CONTEXTS_PARAM] = []
forkedContexts = obj.get(constants.FORKED_CONTEXTS_PARAM)
data = copy.copy(data) or {}
data[constants.FORK_PARAM] = len(forkedContexts)
forkedContexts.append(self.clone(data=data))
def spawn(self,
machineName,
contexts,
countdown=0,
method='POST',
_currentConfig=None):
""" Spawns new machines.
@param machineName the machine to spawn
@param contexts a list of contexts (dictionaries) to spawn the new machine(s) with; multiple contexts will spawn
multiple machines
@param countdown the countdown (in seconds) to wait before spawning machines
@param method the method ('GET' or 'POST') to invoke the machine with (default: POST)
@param _currentConfig test injection for configuration
"""
# using the current task name as a root to startStateMachine will make this idempotent
taskName = self.__obj[constants.TASK_NAME_PARAM]
startStateMachine(machineName,
contexts,
taskName=taskName,
method=method,
countdown=countdown,
_currentConfig=_currentConfig,
headers=self.headers)
def initialize(self):
""" Initializes the FSMContext. Queues a Task (so that we can benefit from auto-retry) to dispatch
an event and take the machine from 'pseudo-init' into the state machine's initial state, as
defined in the fsm.yaml file.
@param data: a dict of initial key, value pairs to stuff into the FSMContext
@return: an event string to dispatch to the FSMContext to put it into the initialState
"""
self[constants.STEPS_PARAM] = 0
task = self.generateInitializationTask()
self.Queue(name=self.queueName).add(task)
_FantasmInstance(key_name=self.instanceName,
instanceName=self.instanceName).put()
return FSM.PSEUDO_INIT
def dispatch(self, event, obj):
""" The main entry point to move the machine according to an event.
@param event: a string event to dispatch to the FSMContext
@param obj: an object that the FSMContext can operate on
@return: an event string to dispatch to the FSMContext
"""
self.__obj = self.__obj or obj # hold the obj object for use during this context
# store the starting state and event for the handleEvent() method
self.startingState = self.currentState
self.startingEvent = event
nextEvent = None
try:
nextEvent = self.currentState.dispatch(self, event, obj)
if obj.get(constants.FORKED_CONTEXTS_PARAM):
# pylint: disable-msg=W0212
# - accessing the protected method is fine here, since it is an instance of the same class
tasks = []
for context in obj[constants.FORKED_CONTEXTS_PARAM]:
context[constants.STEPS_PARAM] = int(
context.get(constants.STEPS_PARAM, '0')) + 1
task = context.queueDispatch(nextEvent, queue=False)
if task: # fan-in magic
if not task.was_enqueued: # fan-in always queues
tasks.append(task)
try:
if tasks:
transition = self.currentState.getTransition(nextEvent)
_queueTasks(self.Queue, transition.queueName, tasks)
except (TaskAlreadyExistsError, TombstonedTaskError):
# unlike a similar block in self.continutation, this is well off the happy path
self.logger.critical(
'Unable to queue fork Tasks %s as it/they already exists. (Machine %s, State %s)',
[task.name for task in tasks if not task.was_enqueued],
self.machineName, self.currentState.name)
if nextEvent:
self[constants.STEPS_PARAM] = int(
self.get(constants.STEPS_PARAM, '0')) + 1
try:
self.queueDispatch(nextEvent)
except (TaskAlreadyExistsError, TombstonedTaskError):
# unlike a similar block in self.continutation, this is well off the happy path
#
# FIXME: when this happens, it means there was failure shortly after queuing the Task, or
# possibly even with queuing the Task. when this happens there is a chance that
# two states in the machine are executing simultaneously, which is may or may not
# be a good thing, depending on what each state does. gracefully handling this
# exception at least means that this state will terminate.
self.logger.critical(
'Unable to queue next Task as it already exists. (Machine %s, State %s)',
self.machineName, self.currentState.name)
else:
# if we're not in a final state, emit a log message
# FIXME - somehow we should avoid this message if we're in the "last" step of a continuation...
if not self.currentState.isFinalState and not obj.get(
constants.TERMINATED_PARAM):
self.logger.critical(
'Non-final state did not emit an event. Machine has terminated in an '
+ 'unknown state. (Machine %s, State %s)' %
(self.machineName, self.currentState.name))
# if it is a final state, then dispatch the pseudo-final event to finalize the state machine
elif self.currentState.isFinalState and self.currentState.exitAction:
self[constants.STEPS_PARAM] = int(
self.get(constants.STEPS_PARAM, '0')) + 1
self.queueDispatch(FSM.PSEUDO_FINAL)
except Exception:
self.logger.exception(
"FSMContext.dispatch is handling the following exception:")
self._handleException(event, obj)
return nextEvent
def continuation(self, nextToken):
""" Performs a continuation be re-queueing an FSMContext Task with a slightly modified continuation
token. self.startingState and self.startingEvent are used in the re-queue, so this can be seen as a
'fork' of the current context.
@param nextToken: the next continuation token
"""
assert not self.get(
constants.INDEX_PARAM) # fan-out after fan-in is not allowed
step = str(self[
constants.STEPS_PARAM]) # needs to be a str key into a json dict
# make a copy and set the currentState to the startingState of this context
context = self.clone()
context.currentState = self.startingState
# update the generation and continuation params
gen = context.get(constants.GEN_PARAM, {})
gen[step] = gen.get(step, 0) + 1
context[constants.GEN_PARAM] = gen
context[constants.CONTINUATION_PARAM] = nextToken
try:
# pylint: disable-msg=W0212
# - accessing the protected method is fine here, since it is an instance of the same class
transition = self.startingState.getTransition(self.startingEvent)
context._queueDispatchNormal(self.startingEvent,
queue=True,
queueName=transition.queueName)
except (TaskAlreadyExistsError, TombstonedTaskError):
# this can happen when currentState.dispatch() previously succeeded in queueing the continuation
# Task, but failed with the doAction.execute() call in a _previous_ execution of this Task.
# NOTE: this prevent the dreaded "fork bomb"
self.logger.info(
'Unable to queue continuation Task as it already exists. (Machine %s, State %s)',
self.machineName, self.currentState.name)
def queueDispatch(self, nextEvent, queue=True):
""" Queues a .dispatch(nextEvent) call in the appengine Task queue.
@param nextEvent: a string event
@param queue: a boolean indicating whether or not to queue a Task, or leave it to the caller
@return: a taskqueue.Task instance which may or may not have been queued already
"""
assert nextEvent is not None
# self.currentState is already transitioned away from self.startingState
transition = self.currentState.getTransition(nextEvent)
if transition.target.isFanIn:
task = self._queueDispatchFanIn(
nextEvent,
fanInPeriod=transition.target.fanInPeriod,
retryOptions=transition.retryOptions,
queueName=transition.queueName)
else:
task = self._queueDispatchNormal(
nextEvent,
queue=queue,
countdown=transition.countdown,
retryOptions=transition.retryOptions,
queueName=transition.queueName)
return task
def _queueDispatchNormal(self,
nextEvent,
queue=True,
countdown=0,
retryOptions=None,
queueName=None):
""" Queues a call to .dispatch(nextEvent) in the appengine Task queue.
@param nextEvent: a string event
@param queue: a boolean indicating whether or not to queue a Task, or leave it to the caller
@param countdown: the number of seconds to countdown before the queued task fires
@param retryOptions: the RetryOptions for the task
@param queueName: the queue name to Queue into
@return: a taskqueue.Task instance which may or may not have been queued already
"""
assert nextEvent is not None
assert queueName
url = self.buildUrl(self.currentState, nextEvent)
params = self.buildParams(self.currentState, nextEvent)
taskName = self.getTaskName(nextEvent)
task = Task(name=taskName,
method=self.method,
url=url,
params=params,
countdown=countdown,
retry_options=retryOptions,
headers=self.headers)
if queue:
self.Queue(name=queueName).add(task)
return task
def _queueDispatchFanIn(self,
nextEvent,
fanInPeriod=0,
retryOptions=None,
queueName=None):
""" Queues a call to .dispatch(nextEvent) in the task queue, or saves the context to the
datastore for processing by the queued .dispatch(nextEvent)
@param nextEvent: a string event
@param fanInPeriod: the period of time between fan in Tasks
@param queueName: the queue name to Queue into
@return: a taskqueue.Task instance which may or may not have been queued already
"""
assert nextEvent is not None
assert not self.get(
constants.INDEX_PARAM) # fan-in after fan-in is not allowed
assert queueName
# we pop this off here because we do not want the fan-out/continuation param as part of the
# task name, otherwise we loose the fan-in - each fan-in gets one work unit.
self.pop(constants.GEN_PARAM, None)
fork = self.pop(constants.FORK_PARAM, None)
taskNameBase = self.getTaskName(nextEvent, fanIn=True)
rwlock = ReadWriteLock(taskNameBase, self)
index = rwlock.currentIndex()
# (***)
#
# grab the lock - memcache.incr()
#
# on Task retry, multiple incr() calls are possible. possible ways to handle:
#
# 1. release the lock in a 'finally' clause, but then risk missing a work
# package because acquiring the read lock will succeed even though the
# work package was not written yet.
#
# 2. allow the lock to get too high. the fan-in logic attempts to wait for
# work packages across multiple-retry attempts, so this seems like the
# best option. we basically trade a bit of latency in fan-in for reliability.
#
rwlock.acquireWriteLock(index, nextEvent=nextEvent)
# insert the work package, which is simply a serialized FSMContext
workIndex = '%s-%d' % (taskNameBase, knuthHash(index))
# on retry, we want to ensure we get the same work index for this task
actualTaskName = self.__obj[constants.TASK_NAME_PARAM]
indexKeyName = 'workIndex-' + '-'.join(
[str(i) for i in [actualTaskName, fork] if i]) or None
semaphore = RunOnceSemaphore(indexKeyName, self)
# check if the workIndex changed during retry
semaphoreWritten = False
if self.__obj[constants.RETRY_COUNT_PARAM] > 0:
# see comment (A) in self._queueDispatchFanIn(...)
time.sleep(constants.DATASTORE_ASYNCRONOUS_INDEX_WRITE_WAIT_TIME)
payload = semaphore.readRunOnceSemaphore(payload=workIndex,
transactional=False)
if payload:
semaphoreWritten = True
if payload != workIndex:
self.logger.info(
"Work index changed from '%s' to '%s' on retry.",
payload, workIndex)
workIndex = payload
# write down two models, one actual work package, one idempotency package
keyName = '-'.join([str(i)
for i in [actualTaskName, fork] if i]) or None
work = _FantasmFanIn(context=self,
workIndex=workIndex,
key_name=keyName)
# close enough to idempotent, but could still write only one of the entities
# FIXME: could be made faster using a bulk put, but this interface is cleaner
if not semaphoreWritten:
semaphore.writeRunOnceSemaphore(payload=workIndex,
transactional=False)
# put the work item
db.put(work)
# (A) now the datastore is asynchronously writing the indices, so the work package may
# not show up in a query for a period of time. there is a corresponding time.sleep()
# in the fan-in of self.mergeJoinDispatch(...)
# release the lock - memcache.decr()
rwlock.releaseWriteLock(index)
try:
# insert a task to run in the future and process a bunch of work packages
now = time.time()
self[constants.INDEX_PARAM] = index
url = self.buildUrl(self.currentState, nextEvent)
params = self.buildParams(self.currentState, nextEvent)
task = Task(name='%s-%d' % (taskNameBase, index),
method=self.method,
url=url,
params=params,
eta=datetime.datetime.utcfromtimestamp(now) +
datetime.timedelta(seconds=fanInPeriod),
headers=self.headers,
retry_options=retryOptions)
self.Queue(name=queueName).add(task)
return task
except (TaskAlreadyExistsError, TombstonedTaskError):
pass # Fan-in magic
def mergeJoinDispatch(self, event, obj):
""" Performs a merge join on the pending fan-in dispatches.
@param event: an event that is being merge joined (destination state must be a fan in)
@return: a list (possibly empty) of FSMContext instances
"""
# this assertion comes from _queueDispatchFanIn - we never want fan-out info in a fan-in context
assert not self.get(constants.GEN_PARAM)
assert not self.get(constants.FORK_PARAM)
# the work package index is stored in the url of the Task/FSMContext
index = self.get(constants.INDEX_PARAM)
taskNameBase = self.getTaskName(event, fanIn=True)
# see comment (***) in self._queueDispatchFanIn
#
# in the case of failing to acquire a read lock (due to failed release of write lock)
# we have decided to keep retrying
raiseOnFail = False
if self._getTaskRetryLimit() is not None:
raiseOnFail = (self._getTaskRetryLimit() >
self.__obj[constants.RETRY_COUNT_PARAM])
rwlock = ReadWriteLock(taskNameBase, self)
rwlock.acquireReadLock(index, raiseOnFail=raiseOnFail)
# and return the FSMContexts list
class FSMContextList(list):
""" A list that supports .logger.info(), .logger.warning() etc.for fan-in actions """
def __init__(self, context, contexts):
""" setup a self.logger for fan-in actions """
super(FSMContextList, self).__init__(contexts)
self.logger = Logger(context)
self.instanceName = context.instanceName
# see comment (A) in self._queueDispatchFanIn(...)
time.sleep(constants.DATASTORE_ASYNCRONOUS_INDEX_WRITE_WAIT_TIME)
# the following step ensure that fan-in only ever operates one time over a list of data
# the entity is created in State.dispatch(...) _after_ all the actions have executed
# successfully
workIndex = '%s-%d' % (taskNameBase, knuthHash(index))
if obj[constants.RETRY_COUNT_PARAM] > 0:
semaphore = RunOnceSemaphore(workIndex, self)
if semaphore.readRunOnceSemaphore(
payload=self.__obj[constants.TASK_NAME_PARAM]):
self.logger.info(
"Fan-in idempotency guard for workIndex '%s', not processing any work items.",
workIndex)
return FSMContextList(self,
[]) # don't operate over the data again
# fetch all the work packages in the current group for processing
query = _FantasmFanIn.all() \
.filter('workIndex =', workIndex) \
.order('__key__')
# construct a list of FSMContexts
contexts = [self.clone(data=r.context) for r in query]
return FSMContextList(self, contexts)
def _getTaskRetryLimit(self):
""" Method that returns the maximum number of retries for this particular dispatch
@param obj: an object that the FSMContext can operate on
"""
# get task_retry_limit configuration
try:
transition = self.startingState.getTransition(self.startingEvent)
taskRetryLimit = transition.retryOptions.task_retry_limit
except UnknownEventError:
# can't find the transition, use the machine-level default
taskRetryLimit = self.retryOptions.task_retry_limit
return taskRetryLimit
def _handleException(self, event, obj):
""" Method for child classes to override to handle exceptions.
@param event: a string event
@param obj: an object that the FSMContext can operate on
"""
retryCount = obj.get(constants.RETRY_COUNT_PARAM, 0)
taskRetryLimit = self._getTaskRetryLimit()
if taskRetryLimit and retryCount >= taskRetryLimit:
# need to permanently fail
self.logger.critical(
'Max-requeues reached. Machine has terminated in an unknown state. '
+ '(Machine %s, State %s, Event %s)',
self.machineName,
self.startingState.name,
event,
exc_info=True)
# re-raise, letting App Engine TaskRetryOptions kill the task
raise
else:
# re-raise the exception
self.logger.warning(
'Exception occurred processing event. Task will be retried. ' +
'(Machine %s, State %s)',
self.machineName,
self.startingState.name,
exc_info=True)
# this line really just allows unit tests to work - the request is really dead at this point
self.currentState = self.startingState
raise
def buildUrl(self, state, event):
""" Builds the taskqueue url.
@param state: the State to dispatch to
@param event: the event to dispatch
@return: a url that can be used to build a taskqueue.Task instance to .dispatch(event)
"""
assert state and event
return self.url + '%s/%s/%s/' % (
state.name, event, state.getTransition(event).target.name)
def buildParams(self, state, event):
""" Builds the taskqueue params.
@param state: the State to dispatch to
@param event: the event to dispatch
@return: a dict suitable to use in constructing a url (GET) or using as params (POST)
"""
assert state and event
params = {
constants.STATE_PARAM: state.name,
constants.EVENT_PARAM: event,
constants.INSTANCE_NAME_PARAM: self.instanceName
}
for key, value in self.items():
if key not in constants.NON_CONTEXT_PARAMS:
if self.contextTypes.get(key) is simplejson.loads:
value = simplejson.dumps(value, cls=models.Encoder)
if isinstance(value, datetime.datetime):
value = str(int(time.mktime(value.utctimetuple())))
if isinstance(value, dict):
# FIXME: should we issue a warning that they should update fsm.yaml?
value = simplejson.dumps(value, cls=models.Encoder)
if isinstance(value, list) and len(value) == 1:
key = key + '[]' # used to preserve lists of length=1 - see handler.py for inverse
params[key] = value
return params
def getTaskName(self, nextEvent, instanceName=None, fanIn=False):
""" Returns a task name that is unique for a specific dispatch
@param nextEvent: the event to dispatch
@return: a task name that can be used to build a taskqueue.Task instance to .dispatch(nextEvent)
"""
transition = self.currentState.getTransition(nextEvent)
parts = []
parts.append(instanceName or self.instanceName)
if self.get(constants.GEN_PARAM):
for (step, gen) in self[constants.GEN_PARAM].items():
parts.append('continuation-%s-%s' % (step, gen))
if self.get(constants.FORK_PARAM):
parts.append('fork-' + str(self[constants.FORK_PARAM]))
# post-fan-in we need to store the workIndex in the task name to avoid duplicates, since
# we popped the generation off during fan-in
# FIXME: maybe not pop the generation in fan-in?
# FIXME: maybe store this in the instanceName?
# FIXME: i wish this was easier to get right :-)
if (not fanIn) and self.get(constants.INDEX_PARAM):
parts.append('work-index-' + str(self[constants.INDEX_PARAM]))
parts.append(self.currentState.name)
parts.append(nextEvent)
parts.append(transition.target.name)
parts.append('step-' + str(self[constants.STEPS_PARAM]))
return '--'.join(parts)
def clone(self, instanceName=None, data=None):
""" Returns a copy of the FSMContext.
@param instanceName: the instance name to optionally apply to the clone
@param data: a dict/mapping of data to optionally apply (.update()) to the clone
@return: a new FSMContext instance
"""
context = copy.deepcopy(self)
if instanceName:
context.instanceName = instanceName
if data:
context.update(data)
return context
class FSMContext(dict):
""" A finite state machine context instance. """
def __init__(self, initialState, currentState=None, machineName=None, instanceName=None,
retryOptions=None, url=None, queueName=None, data=None, contextTypes=None,
method='GET', persistentLogging=False, obj=None, headers=None):
""" Constructor
@param initialState: a State instance
@param currentState: a State instance
@param machineName: the name of the fsm
@param instanceName: the instance name of the fsm
@param retryOptions: the TaskRetryOptions for the machine
@param url: the url of the fsm
@param queueName: the name of the appengine task queue
@param headers: a dict of X-Fantasm request headers to pass along in Tasks
@param persistentLogging: if True, use persistent _FantasmLog model
@param obj: an object that the FSMContext can operate on
"""
assert queueName
super(FSMContext, self).__init__(data or {})
self.initialState = initialState
self.currentState = currentState
self.currentAction = None
if currentState:
self.currentAction = currentState.exitAction
self.machineName = machineName
self.instanceName = instanceName or self._generateUniqueInstanceName()
self.queueName = queueName
self.retryOptions = retryOptions
self.url = url
self.method = method
self.startingEvent = None
self.startingState = None
self.contextTypes = constants.PARAM_TYPES.copy()
if contextTypes:
self.contextTypes.update(contextTypes)
self.logger = Logger(self, obj=obj, persistentLogging=persistentLogging)
self.__obj = obj
self.headers = headers
# the following is monkey-patched from handler.py for 'immediate mode'
from google.appengine.api.taskqueue.taskqueue import Queue
self.Queue = Queue # pylint: disable-msg=C0103
def _generateUniqueInstanceName(self):
""" Generates a unique instance name for this machine.
@return: a FSMContext instanceName that is (pretty darn likely to be) unique
"""
utcnow = datetime.datetime.utcnow()
dateStr = utcnow.strftime('%Y%m%d%H%M%S')
randomStr = ''.join(random.sample(constants.CHARS_FOR_RANDOM, 6))
return '%s-%s-%s' % (self.machineName, dateStr, randomStr)
def putTypedValue(self, key, value):
""" Sets a value on context[key], but casts the value according to self.contextTypes. """
# cast the value to the appropriate type TODO: should this be in FSMContext?
cast = self.contextTypes[key]
kwargs = {}
if cast is simplejson.loads:
kwargs = {'object_hook': models.decode}
if isinstance(value, list):
value = [cast(v, **kwargs) for v in value]
else:
value = cast(value, **kwargs)
# update the context
self[key] = value
def generateInitializationTask(self, countdown=0, taskName=None):
""" Generates a task for initializing the machine. """
assert self.currentState.name == FSM.PSEUDO_INIT
url = self.buildUrl(self.currentState, FSM.PSEUDO_INIT)
params = self.buildParams(self.currentState, FSM.PSEUDO_INIT)
taskName = taskName or self.getTaskName(FSM.PSEUDO_INIT)
task = Task(name=taskName, method=self.method, url=url, params=params, countdown=countdown,
headers=self.headers)
return task
def fork(self, data=None):
""" Forks the FSMContext.
When an FSMContext is forked, an identical copy of the finite state machine is generated
that will have the same event dispatched to it as the machine that called .fork(). The data
parameter is useful for allowing each forked instance to operate on a different bit of data.
@param data: an option mapping of data to apply to the forked FSMContext
"""
obj = self.__obj
if obj.get(constants.FORKED_CONTEXTS_PARAM) is None:
obj[constants.FORKED_CONTEXTS_PARAM] = []
forkedContexts = obj.get(constants.FORKED_CONTEXTS_PARAM)
data = copy.copy(data) or {}
data[constants.FORK_PARAM] = len(forkedContexts)
forkedContexts.append(self.clone(data=data))
def spawn(self, machineName, contexts, countdown=0, method='POST',
_currentConfig=None):
""" Spawns new machines.
@param machineName the machine to spawn
@param contexts a list of contexts (dictionaries) to spawn the new machine(s) with; multiple contexts will spawn
multiple machines
@param countdown the countdown (in seconds) to wait before spawning machines
@param method the method ('GET' or 'POST') to invoke the machine with (default: POST)
@param _currentConfig test injection for configuration
"""
# using the current task name as a root to startStateMachine will make this idempotent
taskName = self.__obj[constants.TASK_NAME_PARAM]
startStateMachine(machineName, contexts, taskName=taskName, method=method, countdown=countdown,
_currentConfig=_currentConfig)
def initialize(self):
""" Initializes the FSMContext. Queues a Task (so that we can benefit from auto-retry) to dispatch
an event and take the machine from 'pseudo-init' into the state machine's initial state, as
defined in the fsm.yaml file.
@param data: a dict of initial key, value pairs to stuff into the FSMContext
@return: an event string to dispatch to the FSMContext to put it into the initialState
"""
self[constants.STEPS_PARAM] = 0
task = self.generateInitializationTask()
self.Queue(name=self.queueName).add(task)
_FantasmInstance(key_name=self.instanceName, instanceName=self.instanceName).put()
return FSM.PSEUDO_INIT
def dispatch(self, event, obj):
""" The main entry point to move the machine according to an event.
@param event: a string event to dispatch to the FSMContext
@param obj: an object that the FSMContext can operate on
@return: an event string to dispatch to the FSMContext
"""
self.__obj = self.__obj or obj # hold the obj object for use during this context
# store the starting state and event for the handleEvent() method
self.startingState = self.currentState
self.startingEvent = event
nextEvent = None
try:
nextEvent = self.currentState.dispatch(self, event, obj)
if obj.get(constants.FORKED_CONTEXTS_PARAM):
# pylint: disable-msg=W0212
# - accessing the protected method is fine here, since it is an instance of the same class
tasks = []
for context in obj[constants.FORKED_CONTEXTS_PARAM]:
context[constants.STEPS_PARAM] = int(context.get(constants.STEPS_PARAM, '0')) + 1
task = context.queueDispatch(nextEvent, queue=False)
if task: # fan-in magic
if not task.was_enqueued: # fan-in always queues
tasks.append(task)
try:
if tasks:
transition = self.currentState.getTransition(nextEvent)
self.Queue(name=transition.queueName).add(tasks)
except (TaskAlreadyExistsError, TombstonedTaskError):
# unlike a similar block in self.continutation, this is well off the happy path
self.logger.critical(
'Unable to queue fork Tasks %s as it/they already exists. (Machine %s, State %s)',
[task.name for task in tasks if not task.was_enqueued],
self.machineName,
self.currentState.name)
if nextEvent:
self[constants.STEPS_PARAM] = int(self.get(constants.STEPS_PARAM, '0')) + 1
try:
self.queueDispatch(nextEvent)
except (TaskAlreadyExistsError, TombstonedTaskError):
# unlike a similar block in self.continutation, this is well off the happy path
#
# FIXME: when this happens, it means there was failure shortly after queuing the Task, or
# possibly even with queuing the Task. when this happens there is a chance that
# two states in the machine are executing simultaneously, which is may or may not
# be a good thing, depending on what each state does. gracefully handling this
# exception at least means that this state will terminate.
self.logger.critical('Unable to queue next Task as it already exists. (Machine %s, State %s)',
self.machineName,
self.currentState.name)
else:
# if we're not in a final state, emit a log message
# FIXME - somehow we should avoid this message if we're in the "last" step of a continuation...
if not self.currentState.isFinalState and not obj.get(constants.TERMINATED_PARAM):
self.logger.critical('Non-final state did not emit an event. Machine has terminated in an ' +
'unknown state. (Machine %s, State %s)' %
(self.machineName, self.currentState.name))
# if it is a final state, then dispatch the pseudo-final event to finalize the state machine
elif self.currentState.isFinalState and self.currentState.exitAction:
self[constants.STEPS_PARAM] = int(self.get(constants.STEPS_PARAM, '0')) + 1
self.queueDispatch(FSM.PSEUDO_FINAL)
except Exception:
self.logger.exception("FSMContext.dispatch is handling the following exception:")
self._handleException(event, obj)
return nextEvent
def continuation(self, nextToken):
""" Performs a continuation be re-queueing an FSMContext Task with a slightly modified continuation
token. self.startingState and self.startingEvent are used in the re-queue, so this can be seen as a
'fork' of the current context.
@param nextToken: the next continuation token
"""
assert not self.get(constants.INDEX_PARAM) # fan-out after fan-in is not allowed
step = str(self[constants.STEPS_PARAM]) # needs to be a str key into a json dict
# make a copy and set the currentState to the startingState of this context
context = self.clone()
context.currentState = self.startingState
# update the generation and continuation params
gen = context.get(constants.GEN_PARAM, {})
gen[step] = gen.get(step, 0) + 1
context[constants.GEN_PARAM] = gen
context[constants.CONTINUATION_PARAM] = nextToken
try:
# pylint: disable-msg=W0212
# - accessing the protected method is fine here, since it is an instance of the same class
transition = self.startingState.getTransition(self.startingEvent)
context._queueDispatchNormal(self.startingEvent, queue=True, queueName=transition.queueName)
except (TaskAlreadyExistsError, TombstonedTaskError):
# this can happen when currentState.dispatch() previously succeeded in queueing the continuation
# Task, but failed with the doAction.execute() call in a _previous_ execution of this Task.
# NOTE: this prevent the dreaded "fork bomb"
self.logger.info('Unable to queue continuation Task as it already exists. (Machine %s, State %s)',
self.machineName,
self.currentState.name)
def queueDispatch(self, nextEvent, queue=True):
""" Queues a .dispatch(nextEvent) call in the appengine Task queue.
@param nextEvent: a string event
@param queue: a boolean indicating whether or not to queue a Task, or leave it to the caller
@return: a taskqueue.Task instance which may or may not have been queued already
"""
assert nextEvent is not None
# self.currentState is already transitioned away from self.startingState
transition = self.currentState.getTransition(nextEvent)
if transition.target.isFanIn:
task = self._queueDispatchFanIn(nextEvent, fanInPeriod=transition.target.fanInPeriod,
queueName=transition.queueName)
else:
task = self._queueDispatchNormal(nextEvent, queue=queue, countdown=transition.countdown,
retryOptions=transition.retryOptions,
queueName=transition.queueName)
return task
def _queueDispatchNormal(self, nextEvent, queue=True, countdown=0, retryOptions=None, queueName=None):
""" Queues a call to .dispatch(nextEvent) in the appengine Task queue.
@param nextEvent: a string event
@param queue: a boolean indicating whether or not to queue a Task, or leave it to the caller
@param countdown: the number of seconds to countdown before the queued task fires
@param retryOptions: the RetryOptions for the task
@param queueName: the queue name to Queue into
@return: a taskqueue.Task instance which may or may not have been queued already
"""
assert nextEvent is not None
assert queueName
url = self.buildUrl(self.currentState, nextEvent)
params = self.buildParams(self.currentState, nextEvent)
taskName = self.getTaskName(nextEvent)
task = Task(name=taskName, method=self.method, url=url, params=params, countdown=countdown,
retry_options=retryOptions, headers=self.headers)
if queue:
self.Queue(name=queueName).add(task)
return task
def _queueDispatchFanIn(self, nextEvent, fanInPeriod=0, queueName=None):
""" Queues a call to .dispatch(nextEvent) in the task queue, or saves the context to the
datastore for processing by the queued .dispatch(nextEvent)
@param nextEvent: a string event
@param fanInPeriod: the period of time between fan in Tasks
@param queueName: the queue name to Queue into
@return: a taskqueue.Task instance which may or may not have been queued already
"""
assert nextEvent is not None
assert not self.get(constants.INDEX_PARAM) # fan-in after fan-in is not allowed
assert queueName
# we pop this off here because we do not want the fan-out/continuation param as part of the
# task name, otherwise we loose the fan-in - each fan-in gets one work unit.
self.pop(constants.GEN_PARAM, None)
self.pop(constants.FORK_PARAM, None)
taskNameBase = self.getTaskName(nextEvent, fanIn=True)
index = memcache.get('index-' + taskNameBase)
if index is None:
# using 'random.randint' here instead of '1' helps when the index is ejected from memcache
# instead of restarting at the same counter, we jump (likely) far way from existing task job
# names.
memcache.add('index-' + taskNameBase, random.randint(1, 2**32))
index = memcache.get('index-' + taskNameBase)
# grab the lock
lock = '%s-lock-%d' % (taskNameBase, index)
writers = memcache.incr(lock, initial_value=2**16)
if writers < 2**16:
memcache.decr(lock)
# this will escape as a 500 error and the Task will be re-tried by appengine
raise FanInWriteLockFailureRuntimeError(nextEvent,
self.machineName,
self.currentState.name,
self.instanceName)
# insert the work package, which is simply a serialized FSMContext
workIndex = '%s-%d' % (taskNameBase, knuthHash(index))
work = _FantasmFanIn(context=self, workIndex=workIndex)
work.put()
# insert a task to run in the future and process a bunch of work packages
now = time.time()
try:
self[constants.INDEX_PARAM] = index
url = self.buildUrl(self.currentState, nextEvent)
params = self.buildParams(self.currentState, nextEvent)
# int(now / (fanInPeriod - 1 + 30)) included because it was in [2], but is less needed now that
# we use random.randint in seeding memcache. for long fan in periods, and the case where random.randint
# hits the same value twice, this may cause problems for up to fanInPeriod + 30s.
# see: http://www.mail-archive.com/[email protected]/msg30408.html
task = Task(name='%s-%d-%d' % (taskNameBase, int(now / (fanInPeriod - 1 + 30)), index),
method=self.method,
url=url,
params=params,
eta=datetime.datetime.utcfromtimestamp(now) + datetime.timedelta(seconds=fanInPeriod),
headers=self.headers)
self.Queue(name=queueName).add(task)
return task
except (TaskAlreadyExistsError, TombstonedTaskError):
pass # Fan-in magic
finally:
memcache.decr(lock)
def mergeJoinDispatch(self, event, obj):
""" Performs a merge join on the pending fan-in dispatches.
@param event: an event that is being merge joined (destination state must be a fan in)
@return: a list (possibly empty) of FSMContext instances
"""
# this assertion comes from _queueDispatchFanIn - we never want fan-out info in a fan-in context
assert not self.get(constants.GEN_PARAM)
assert not self.get(constants.FORK_PARAM)
# the work package index is stored in the url of the Task/FSMContext
index = self.get(constants.INDEX_PARAM)
taskNameBase = self.getTaskName(event, fanIn=True)
# tell writers to use another index
memcache.incr('index-' + taskNameBase)
lock = '%s-lock-%d' % (taskNameBase, index)
memcache.decr(lock, 2**15) # tell writers they missed the boat
# 20 iterations * 0.25s = 5s total wait time
busyWaitIters = 20
busyWaitIterSecs = 0.250
# busy wait for writers
for i in xrange(busyWaitIters):
counter = memcache.get(lock)
# counter is None --> ejected from memcache
# int(counter) <= 2**15 --> writers have all called memcache.decr
if counter is None or int(counter) <= 2**15:
break
time.sleep(busyWaitIterSecs)
self.logger.debug("Tried to acquire lock '%s' %d times...", lock, i + 1)
# FIXME: is there anything else that can be done? will work packages be lost? maybe queue another task
# to sweep up later?
if i >= (busyWaitIters - 1): # pylint: disable-msg=W0631
self.logger.error("Gave up waiting for all fan-in work items.")
# at this point we could have two tasks trying to process the same work packages. in the
# happy path this will not likely happen because the tasks are sent off with different ETAs,
# however in the unhappy path, it is possible for multiple tasks to be executing (retry on
# 500 etc.). we solve this with a read lock using memcache.
#
# FIXME: would using a transaction on db.delete work if using ancestors? one task would win the
# race to delete the the work based on a transaction error?
readlock = '%s-readlock-%d' % (taskNameBase, index)
haveReadLock = False
try:
# put the actual name of the winning task into to lock
actualTaskName = self.get(constants.TASK_NAME_PARAM)
added = memcache.add(readlock, actualTaskName, time=30) # FIXME: is 30s appropriate?
lockValue = memcache.get(readlock)
# and return the FSMContexts list
class FSMContextList(list):
""" A list that supports .logger.info(), .logger.warning() etc.for fan-in actions """
def __init__(self, context, contexts):
""" setup a self.logger for fan-in actions """
super(FSMContextList, self).__init__(contexts)
self.logger = Logger(context)
self.instanceName = context.instanceName
# if the lock value is not equal to the added value, it means this task lost the race
if not added or lockValue != actualTaskName:
return FSMContextList(self, [])
# raise FanInReadLockFailureRuntimeError(event,
# self.machineName,
# self.currentState.name,
# self.instanceName)
# flag used in finally block to decide whether or not to log an error message
haveReadLock = True
# fetch all the work packages in the current group for processing
workIndex = '%s-%d' % (taskNameBase, knuthHash(index))
query = _FantasmFanIn.all() \
.filter('workIndex =', workIndex) \
.order('__key__')
# iterate over the query to fetch results - this is done in 'small batches'
fanInResults = list(query)
# construct a list of FSMContexts
contexts = [self.clone(data=r.context) for r in fanInResults]
# hold the fanInResult around in case we need to re-put them (on an Exception)
obj[constants.FAN_IN_RESULTS_PARAM] = fanInResults
# and delete the work packages - bearing in mind appengine limits
maxDeleteSize = 250 # appengine does not like to delete > 500 models at a time, 250 is a nice safe number
if len(fanInResults) > maxDeleteSize:
self.logger.warning("%d contexts in the current batch. Consider decreasing fan-in.", len(fanInResults))
i = 0
while fanInResults[i:i+maxDeleteSize]:
db.delete(fanInResults[i:i+maxDeleteSize])
i += maxDeleteSize
return FSMContextList(self, contexts)
finally:
deleted = memcache.delete(readlock)
# FIXME: is there anything else that can be done?
if haveReadLock and deleted == memcache.DELETE_NETWORK_FAILURE:
self.logger.error("Unable to release the fan in read lock.")
def _getTaskRetryLimit(self):
""" Method that returns the maximum number of retries for this particular dispatch
@param obj: an object that the FSMContext can operate on
"""
# get task_retry_limit configuration
try:
transition = self.startingState.getTransition(self.startingEvent)
taskRetryLimit = transition.retryOptions.task_retry_limit
except UnknownEventError:
# can't find the transition, use the machine-level default
taskRetryLimit = self.retryOptions.task_retry_limit
return taskRetryLimit
def _handleException(self, event, obj):
""" Method for child classes to override to handle exceptions.
@param event: a string event
@param obj: an object that the FSMContext can operate on
"""
retryCount = obj.get(constants.RETRY_COUNT_PARAM, 0)
taskRetryLimit = self._getTaskRetryLimit()
if taskRetryLimit and retryCount >= taskRetryLimit:
# need to permanently fail
self.logger.critical('Max-requeues reached. Machine has terminated in an unknown state. ' +
'(Machine %s, State %s, Event %s)',
self.machineName, self.startingState.name, event, exc_info=True)
# re-raise, letting App Engine TaskRetryOptions kill the task
raise
else:
# re-raise the exception
self.logger.warning('Exception occurred processing event. Task will be retried. ' +
'(Machine %s, State %s)',
self.machineName, self.startingState.name, exc_info=True)
# re-put fan-in work packages
if obj.get(constants.FAN_IN_RESULTS_PARAM):
try:
fanInResults = obj[constants.FAN_IN_RESULTS_PARAM]
maxPutSize = 250 # put in chunks, rather than the entire list which could be large
i = 0
while(fanInResults[i:i+maxPutSize]):
db.put(fanInResults[i:i+maxPutSize])
i += maxPutSize
except Exception:
self.logger.critical("Unable to re.put() for workIndex = %s", self.fanInResults[0].workIndex)
raise
# this line really just allows unit tests to work - the request is really dead at this point
self.currentState = self.startingState
raise
def buildUrl(self, state, event):
""" Builds the taskqueue url.
@param state: the State to dispatch to
@param event: the event to dispatch
@return: a url that can be used to build a taskqueue.Task instance to .dispatch(event)
"""
assert state and event
return self.url + '%s/%s/%s/' % (state.name,
event,
state.getTransition(event).target.name)
def buildParams(self, state, event):
""" Builds the taskqueue params.
@param state: the State to dispatch to
@param event: the event to dispatch
@return: a dict suitable to use in constructing a url (GET) or using as params (POST)
"""
assert state and event
params = {constants.STATE_PARAM: state.name,
constants.EVENT_PARAM: event,
constants.INSTANCE_NAME_PARAM: self.instanceName}
for key, value in self.items():
if key not in constants.NON_CONTEXT_PARAMS:
if self.contextTypes.get(key) is simplejson.loads:
value = simplejson.dumps(value, cls=models.Encoder)
if isinstance(value, datetime.datetime):
value = str(int(time.mktime(value.utctimetuple())))
if isinstance(value, dict):
# FIXME: should we issue a warning that they should update fsm.yaml?
value = simplejson.dumps(value, cls=models.Encoder)
if isinstance(value, list) and len(value) == 1:
key = key + '[]' # used to preserve lists of length=1 - see handler.py for inverse
params[key] = value
return params
def getTaskName(self, nextEvent, instanceName=None, fanIn=False):
""" Returns a task name that is unique for a specific dispatch
@param nextEvent: the event to dispatch
@return: a task name that can be used to build a taskqueue.Task instance to .dispatch(nextEvent)
"""
transition = self.currentState.getTransition(nextEvent)
parts = []
parts.append(instanceName or self.instanceName)
if self.get(constants.GEN_PARAM):
for (step, gen) in self[constants.GEN_PARAM].items():
parts.append('continuation-%s-%s' % (step, gen))
if self.get(constants.FORK_PARAM):
parts.append('fork-' + str(self[constants.FORK_PARAM]))
# post-fan-in we need to store the workIndex in the task name to avoid duplicates, since
# we popped the generation off during fan-in
# FIXME: maybe not pop the generation in fan-in?
# FIXME: maybe store this in the instanceName?
# FIXME: i wish this was easier to get right :-)
if (not fanIn) and self.get(constants.INDEX_PARAM):
parts.append('work-index-' + str(self[constants.INDEX_PARAM]))
parts.append(self.currentState.name)
parts.append(nextEvent)
parts.append(transition.target.name)
parts.append('step-' + str(self[constants.STEPS_PARAM]))
return '--'.join(parts)
def clone(self, instanceName=None, data=None):
""" Returns a copy of the FSMContext.
@param instanceName: the instance name to optionally apply to the clone
@param data: a dict/mapping of data to optionally apply (.update()) to the clone
@return: a new FSMContext instance
"""
context = copy.deepcopy(self)
if instanceName:
context.instanceName = instanceName
if data:
context.update(data)
return context
