def check_task_trigger(self, state: State,
upstream_states: Dict[Edge, State]) -> State:
"""
Checks if the task's trigger function passes.
Args:
- state (State): the current state of this task
- upstream_states (Dict[Edge, Union[State, List[State]]]): the upstream states
Returns:
- State: the state of the task after running the check
Raises:
- ENDRUN: if the trigger raises an error
"""
try:
if not self.task.trigger(upstream_states):
raise signals.TRIGGERFAIL(message="Trigger failed")
except signals.PrefectStateSignal as exc:
self.logger.debug(
"Task '{name}': {signal} signal raised during execution.".
format(
name=prefect.context.get("task_full_name", self.task.name),
signal=type(exc).__name__,
))
if prefect.context.get("raise_on_exception"):
raise exc
raise ENDRUN(exc.state) from exc
# Exceptions are trapped and turned into TriggerFailed states
except Exception as exc:
self.logger.exception(
"Task '{name}': unexpected error while evaluating task trigger: {exc}"
.format(
exc=repr(exc),
name=prefect.context.get("task_full_name", self.task.name),
))
if prefect.context.get("raise_on_exception"):
raise exc
raise ENDRUN(
TriggerFailed(
"Unexpected error while checking task trigger: {}".format(
repr(exc)),
result=exc,
)) from exc
return state
def check_upstream_skipped(self, state: State,
upstream_states: Dict[Edge, State]) -> State:
"""
Checks if any of the upstream tasks have skipped.
Args:
- state (State): the current state of this task
- upstream_states (Dict[Edge, State]): the upstream states
Returns:
- State: the state of the task after running the check
"""
all_states = set() # type: Set[State]
for edge, upstream_state in upstream_states.items():
# if the upstream state is Mapped, and this task is also mapped,
# we want each individual child to determine if it should
# skip or not based on its upstream parent in the mapping
if isinstance(upstream_state, Mapped) and not edge.mapped:
all_states.update(upstream_state.map_states)
else:
all_states.add(upstream_state)
if self.task.skip_on_upstream_skip and any(s.is_skipped()
for s in all_states):
self.logger.debug(
"Task '{name}': Upstream states were skipped; ending run.".
format(name=prefect.context.get("task_full_name",
self.task.name)))
raise ENDRUN(state=Skipped(message=(
"Upstream task was skipped; if this was not the intended "
"behavior, consider changing `skip_on_upstream_skip=False` "
"for this task.")))
return state
def set_task_to_running(self, state: State, inputs: Dict[str,
Result]) -> State:
"""
Sets the task to running
Args:
- state (State): the current state of this task
- inputs (Dict[str, Result]): a dictionary of inputs whose keys correspond
to the task's `run()` arguments.
Returns:
- State: the state of the task after running the check
Raises:
- ENDRUN: if the task is not ready to run
"""
if not state.is_pending():
self.logger.debug(
"Task '{name}': can't set state to Running because it "
"isn't Pending; ending run.".format(name=prefect.context.get(
"task_full_name", self.task.name)))
raise ENDRUN(state)
new_state = Running(message="Starting task run.")
return new_state
def check_upstream_skipped(self, state: State,
upstream_states: Dict[Edge, State]) -> State:
"""
Checks if any of the upstream tasks have skipped.
Args:
- state (State): the current state of this task
- upstream_states (Dict[Edge, State]): the upstream states
Returns:
- State: the state of the task after running the check
"""
all_states = set() # type: Set[State]
for upstream_state in upstream_states.values():
if isinstance(upstream_state, Mapped):
all_states.update(upstream_state.map_states)
else:
all_states.add(upstream_state)
if self.task.skip_on_upstream_skip and any(s.is_skipped()
for s in all_states):
self.logger.debug(
"Task '{name}': Upstream states were skipped; ending run.".
format(name=prefect.context.get("task_full_name",
self.task.name)))
raise ENDRUN(state=Skipped(message=(
"Upstream task was skipped; if this was not the intended "
"behavior, consider changing `skip_on_upstream_skip=False` "
"for this task.")))
return state
def get_task_run_state(
self,
state: State,
inputs: Dict[str, Result],
timeout_handler: Optional[Callable],
) -> State:
"""
Runs the task and traps any signals or errors it raises.
Also checkpoints the result of a successful task, if `task.checkpoint` is `True`.
Args:
- state (State): the current state of this task
- inputs (Dict[str, Result], optional): a dictionary of inputs whose keys correspond
to the task's `run()` arguments.
- timeout_handler (Callable, optional): function for timing out
task execution, with call signature `handler(fn, *args, **kwargs)`. Defaults to
`prefect.utilities.executors.main_thread_timeout`
Returns:
- State: the state of the task after running the check
Raises:
- signals.PAUSE: if the task raises PAUSE
- ENDRUN: if the task is not ready to run
"""
if not state.is_running():
self.logger.debug(
"Task '{name}': can't run task because it's not in a "
"Running state; ending run.".format(name=prefect.context.get(
"task_full_name", self.task.name)))
raise ENDRUN(state)
try:
self.logger.debug(
"Task '{name}': Calling task.run() method...".format(
name=prefect.context.get("task_full_name",
self.task.name)))
timeout_handler = timeout_handler or main_thread_timeout
raw_inputs = {k: r.value for k, r in inputs.items()}
result = timeout_handler(self.task.run,
timeout=self.task.timeout,
**raw_inputs)
# inform user of timeout
except TimeoutError as exc:
if prefect.context.get("raise_on_exception"):
raise exc
state = TimedOut("Task timed out during execution.",
result=exc,
cached_inputs=inputs)
return state
result = Result(value=result, result_handler=self.result_handler)
state = Success(result=result, message="Task run succeeded.")
if state.is_successful() and self.task.checkpoint is True:
state._result.store_safe_value()
return state
def load_results(
self, state: State,
upstream_states: Dict[Edge,
State]) -> Tuple[State, Dict[Edge, State]]:
"""
Given the task's current state and upstream states, populates all relevant result objects for this task run.
Args:
- state (State): the task's current state.
- upstream_states (Dict[Edge, State]): the upstream state_handlers
Returns:
- Tuple[State, dict]: a tuple of (state, upstream_states)
"""
upstream_results = {}
try:
for edge, upstream_state in upstream_states.items():
upstream_states[edge] = upstream_state.load_result(
edge.upstream_task.result or self.default_result)
if edge.key is not None:
upstream_results[edge.key] = (edge.upstream_task.result
or self.default_result)
state.load_cached_results(upstream_results)
return state, upstream_states
except Exception as exc:
new_state = Failed(
message=f"Failed to retrieve task results: {exc}", result=exc)
final_state = self.handle_state_change(old_state=state,
new_state=new_state)
raise ENDRUN(final_state)
def check_upstream_finished(
self, state: State, upstream_states: Dict[Edge, State]
) -> State:
"""
Checks if the upstream tasks have all finshed.
Args:
- state (State): the current state of this task
- upstream_states (Dict[Edge, Union[State, List[State]]]): the upstream states
Returns:
- State: the state of the task after running the check
Raises:
- ENDRUN: if upstream tasks are not finished.
"""
all_states = set() # type: Set[State]
for edge, upstream_state in upstream_states.items():
# if the upstream state is Mapped, and this task is also mapped,
# we want each individual child to determine if it should
# proceed or not based on its upstream parent in the mapping
if isinstance(upstream_state, Mapped) and not edge.mapped:
all_states.update(upstream_state.map_states)
else:
all_states.add(upstream_state)
if not all(s.is_finished() for s in all_states):
self.logger.debug(
"Task '{name}': not all upstream states are finished; ending run.".format(
name=prefect.context.get("task_full_name", self.task.name)
)
)
raise ENDRUN(state)
return state
def call_runner_target_handlers(self, old_state: State,
new_state: State) -> State:
"""
A special state handler that the FlowRunner uses to call its flow's state handlers.
This method is called as part of the base Runner's `handle_state_change()` method.
Args:
- old_state (State): the old (previous) state
- new_state (State): the new (current) state
Returns:
- State: the new state
"""
raise_on_exception = prefect.context.get("raise_on_exception", False)
try:
new_state = super().call_runner_target_handlers(
old_state=old_state, new_state=new_state)
except Exception as exc:
msg = "Exception raised while calling state handlers: {}".format(
repr(exc))
self.logger.debug(msg)
if raise_on_exception:
raise exc
new_state = Failed(msg, result=exc)
flow_run_id = prefect.context.get("flow_run_id", None)
version = prefect.context.get("flow_run_version")
try:
cloud_state = new_state
state = self.client.set_flow_run_state(flow_run_id=flow_run_id,
version=version,
state=cloud_state)
except Exception as exc:
self.logger.debug("Failed to set flow state with error: {}".format(
repr(exc)))
raise ENDRUN(state=new_state)
if state.is_queued():
state.state = old_state # type: ignore
raise ENDRUN(state=state)
prefect.context.update(flow_run_version=version + 1)
return new_state
def check_task_reached_start_time(self, state: State) -> State:
"""
Checks if a task is in a Scheduled state and, if it is, ensures that the scheduled
time has been reached. Note: Scheduled states include Retry states. Scheduled
states with no start time (`start_time = None`) are never considered ready;
they must be manually placed in another state.
Args:
- state (State): the current state of this task
Returns:
- State: the state of the task after performing the check
Raises:
- ENDRUN: if the task is Scheduled with a future scheduled time
"""
if isinstance(state, Scheduled):
# handle case where no start_time is set
if state.start_time is None:
self.logger.debug(
"Task '{name}' is scheduled without a known start_time; "
"ending run.".format(
name=prefect.context.get("task_full_name", self.task.name)
)
)
raise ENDRUN(state)
# handle case where start time is in the future
elif state.start_time and state.start_time > pendulum.now("utc"):
self.logger.debug(
"Task '{name}': start_time has not been reached; "
"ending run.".format(
name=prefect.context.get("task_full_name", self.task.name)
)
)
raise ENDRUN(state)
return state
def check_task_ready_to_map(
self, state: State, upstream_states: Dict[Edge, State]
) -> State:
"""
Checks if the parent task is ready to proceed with mapping.
Args:
- state (State): the current state of this task
- upstream_states (Dict[Edge, Union[State, List[State]]]): the upstream states
Raises:
- ENDRUN: either way, we dont continue past this point
"""
if state.is_mapped():
raise ENDRUN(state)
# we can't map if there are no success states with iterables upstream
if upstream_states and not any(
[
edge.mapped and state.is_successful()
for edge, state in upstream_states.items()
]
):
new_state = Failed("No upstream states can be mapped over.") # type: State
raise ENDRUN(new_state)
elif not all(
[
hasattr(state.result, "__getitem__")
for edge, state in upstream_states.items()
if state.is_successful() and not state.is_mapped() and edge.mapped
]
):
new_state = Failed("At least one upstream state has an unmappable result.")
raise ENDRUN(new_state)
else:
new_state = Mapped("Ready to proceed with mapping.")
raise ENDRUN(new_state)
def call_runner_target_handlers(self, old_state: State,
new_state: State) -> State:
"""
A special state handler that the TaskRunner uses to call its task's state handlers.
This method is called as part of the base Runner's `handle_state_change()` method.
Args:
- old_state (State): the old (previous) state
- new_state (State): the new (current) state
Returns:
- State: the new state
"""
raise_on_exception = prefect.context.get("raise_on_exception", False)
try:
new_state = super().call_runner_target_handlers(
old_state=old_state, new_state=new_state)
except Exception as exc:
msg = "Exception raised while calling state handlers: {}".format(
repr(exc))
self.logger.debug(msg)
if raise_on_exception:
raise exc
new_state = Failed(msg, result=exc)
task_run_id = prefect.context.get("task_run_id")
version = prefect.context.get("task_run_version")
try:
cloud_state = prepare_state_for_cloud(new_state)
self.client.set_task_run_state(
task_run_id=task_run_id,
version=version,
state=cloud_state,
cache_for=self.task.cache_for,
)
except Exception as exc:
self.logger.debug("Failed to set task state with error: {}".format(
repr(exc)))
raise ENDRUN(state=ClientFailed(state=new_state))
if version is not None:
prefect.context.update(task_run_version=version +
1) # type: ignore
return new_state
def initialize_run( # type: ignore
self, state: Optional[State],
context: Dict[str, Any]) -> TaskRunnerInitializeResult:
"""
Initializes the Task run by initializing state and context appropriately.
Args:
- state (Optional[State]): the initial state of the run
- context (Dict[str, Any]): the context to be updated with relevant information
Returns:
- tuple: a tuple of the updated state, context, and upstream_states objects
"""
# if the map_index is not None, this is a dynamic task and we need to load
# task run info for it
map_index = context.get("map_index")
if map_index not in [-1, None]:
try:
task_run_info = self.client.get_task_run_info(
flow_run_id=context.get("flow_run_id", ""),
task_id=context.get("task_id", ""),
map_index=map_index,
)
# if state was provided, keep it; otherwise use the one from db
state = state or task_run_info.state # type: ignore
context.update(
task_run_id=task_run_info.id, # type: ignore
task_run_version=task_run_info.version, # type: ignore
)
except Exception as exc:
self.logger.exception(
"Failed to retrieve task state with error: {}".format(
repr(exc)))
if state is None:
state = Failed(
message="Could not retrieve state from Prefect Cloud",
result=exc,
)
raise ENDRUN(state=state) from exc
# we assign this so it can be shared with heartbeat thread
self.task_run_id = context.get("task_run_id", "") # type: str
context.update(checkpointing=True)
return super().initialize_run(state=state, context=context)
def get_task_inputs(
self, state: State,
upstream_states: Dict[Edge, State]) -> Dict[str, Result]:
"""
Given the task's current state and upstream states, generates the inputs for this task.
Upstream state result values are used. If the current state has `cached_inputs`, they
will override any upstream values.
Args:
- state (State): the task's current state.
- upstream_states (Dict[Edge, State]): the upstream state_handlers
Returns:
- Dict[str, Result]: the task inputs
"""
task_inputs = super().get_task_inputs(state, upstream_states)
try:
## for mapped tasks, we need to take extra steps to store the cached_inputs;
## this is because in the event of a retry we don't want to have to load the
## entire upstream array that is being mapped over, instead we need store the
## individual pieces of data separately for more efficient retries
map_index = prefect.context.get("map_index")
if map_index not in [-1, None]:
for edge, upstream_state in upstream_states.items():
if (edge.key and edge.mapped
and edge.upstream_task.checkpoint is not False):
try:
task_inputs[edge.key] = task_inputs[
edge.key].write( # type: ignore
task_inputs[edge.key].value,
filename=f"{edge.key}-{map_index}",
**prefect.context,
)
except NotImplementedError:
pass
except Exception as exc:
new_state = Failed(
message=f"Failed to save inputs for mapped task: {exc}",
result=exc)
final_state = self.handle_state_change(old_state=state,
new_state=new_state)
raise ENDRUN(final_state)
return task_inputs
def set_flow_to_running(self, state: State) -> State:
"""
Puts Pending flows in a Running state; leaves Running flows Running.
Args:
- state (State): the current state of this flow
Returns:
- State: the state of the flow after running the check
Raises:
- ENDRUN: if the flow is not pending or running
"""
if state.is_pending():
return Running(message="Running flow.")
elif state.is_running():
return state
else:
raise ENDRUN(state)
def set_task_to_running(self, state: State) -> State:
"""
Sets the task to running
Args:
- state (State): the current state of this task
Returns:
- State: the state of the task after running the check
Raises:
- ENDRUN: if the task is not ready to run
"""
if not state.is_pending():
self.logger.debug(
"Task '{name}': can't set state to Running because it "
"isn't Pending; ending run.".format(name=prefect.context.get(
"task_full_name", self.task.name)))
raise ENDRUN(state)
return Running(message="Starting task run.")
def check_flow_reached_start_time(self, state: State) -> State:
"""
Checks if the Flow is in a Scheduled state and, if it is, ensures that the scheduled
time has been reached.
Args:
- state (State): the current state of this Flow
Returns:
- State: the state of the flow after performing the check
Raises:
- ENDRUN: if the flow is Scheduled with a future scheduled time
"""
if isinstance(state, Scheduled):
if state.start_time and state.start_time > pendulum.now("utc"):
self.logger.debug(
"Flow '{name}': start_time has not been reached; ending run."
.format(name=self.flow.name))
raise ENDRUN(state)
return state
def check_upstream_finished(self, state: State,
upstream_states: Dict[Edge, State]) -> State:
"""
Checks if the upstream tasks have all finshed.
Args:
- state (State): the current state of this task
- upstream_states (Dict[Edge, Union[State, List[State]]]): the upstream states
Returns:
- State: the state of the task after running the check
Raises:
- ENDRUN: if upstream tasks are not finished.
"""
if not all(s.is_finished() for s in upstream_states.values()):
self.logger.debug(
"Task '{name}': not all upstream states are finished; ending run."
.format(name=prefect.context.get("task_full_name",
self.task.name)))
raise ENDRUN(state)
return state
def check_task_reached_start_time(self, state: State) -> State:
"""
Checks if a task is in a Scheduled state and, if it is, ensures that the scheduled
time has been reached. Note: Scheduled states include Retry states.
Args:
- state (State): the current state of this task
Returns:
- State: the state of the task after performing the check
Raises:
- ENDRUN: if the task is Scheduled with a future scheduled time
"""
if isinstance(state, Scheduled):
if state.start_time and state.start_time > pendulum.now("utc"):
self.logger.debug(
"Task '{name}': start_time has not been reached; ending run."
.format(name=prefect.context.get("task_full_name",
self.task.name)))
raise ENDRUN(state)
return state
def get_task_run_state(self, state: State, inputs: Dict[str,
Result]) -> State:
"""
Runs the task and traps any signals or errors it raises.
Also checkpoints the result of a successful task, if `task.checkpoint` is `True`.
Args:
- state (State): the current state of this task
- inputs (Dict[str, Result], optional): a dictionary of inputs whose keys correspond
to the task's `run()` arguments.
Returns:
- State: the state of the task after running the check
Raises:
- signals.PAUSE: if the task raises PAUSE
- ENDRUN: if the task is not ready to run
"""
task_name = prefect.context.get("task_full_name", self.task.name)
if not state.is_running():
self.logger.debug(
f"Task {task_name!r}: Can't run task because it's not in a Running "
"state; ending run.")
raise ENDRUN(state)
value = None
raw_inputs = {k: r.value for k, r in inputs.items()}
new_state = None
try:
self.logger.debug(
f"Task {task_name!r}: Calling task.run() method...")
# Create a stdout redirect if the task has log_stdout enabled
log_context = (
redirect_stdout(
prefect.utilities.logging.RedirectToLog(self.logger))
if getattr(self.task, "log_stdout", False) else nullcontext()
) # type: AbstractContextManager
with log_context:
value = prefect.utilities.executors.run_task_with_timeout(
task=self.task,
args=(),
kwargs=raw_inputs,
logger=self.logger,
)
except TaskTimeoutSignal as exc: # Convert timeouts to a `TimedOut` state
if prefect.context.get("raise_on_exception"):
raise exc
state = TimedOut("Task timed out during execution.", result=exc)
return state
except signals.LOOP as exc: # Convert loop signals to a `Looped` state
new_state = exc.state
assert isinstance(new_state, Looped)
value = new_state.result
new_state.message = exc.state.message or "Task is looping ({})".format(
new_state.loop_count)
except signals.SUCCESS as exc:
# Success signals can be treated like a normal result
new_state = exc.state
assert isinstance(new_state, Success)
value = new_state.result
except Exception as exc: # Handle exceptions in the task
if prefect.context.get("raise_on_exception"):
raise
self.logger.error(
f"Task {task_name!r}: Exception encountered during task execution!",
exc_info=True,
)
state = Failed(f"Error during execution of task: {exc!r}",
result=exc)
return state
# checkpoint tasks if a result is present, except for when the user has opted out by
# disabling checkpointing
if (prefect.context.get("checkpointing") is True
and self.task.checkpoint is not False and value is not None):
try:
formatting_kwargs = {
**prefect.context.get("parameters", {}).copy(),
**prefect.context,
**raw_inputs,
}
result = self.result.write(value, **formatting_kwargs)
except ResultNotImplementedError:
result = self.result.from_value(value=value)
else:
result = self.result.from_value(value=value)
if new_state is not None:
new_state.result = result
return new_state
state = Success(result=result, message="Task run succeeded.")
return state
def run(
self,
state: State = None,
upstream_states: Dict[Edge, State] = None,
context: Dict[str, Any] = None,
executor: "prefect.engine.executors.Executor" = None,
) -> State:
"""
The main endpoint for TaskRunners. Calling this method will conditionally execute
`self.task.run` with any provided inputs, assuming the upstream dependencies are in a
state which allow this Task to run.
Args:
- state (State, optional): initial `State` to begin task run from;
defaults to `Pending()`
- upstream_states (Dict[Edge, State]): a dictionary
representing the states of any tasks upstream of this one. The keys of the
dictionary should correspond to the edges leading to the task.
- context (dict, optional): prefect Context to use for execution
- executor (Executor, optional): executor to use when performing
computation; defaults to the executor specified in your prefect configuration
Returns:
- `State` object representing the final post-run state of the Task
"""
upstream_states = upstream_states or {}
context = context or {}
map_index = context.setdefault("map_index", None)
context["task_full_name"] = "{name}{index}".format(
name=self.task.name,
index=("" if map_index is None else "[{}]".format(map_index)),
)
if executor is None:
executor = prefect.engine.get_default_executor_class()()
# if mapped is true, this task run is going to generate a Mapped state. It won't
# actually run, but rather spawn children tasks to map over its inputs. We
# detect this case by checking for:
# - upstream edges that are `mapped`
# - no `map_index` (which indicates that this is the child task, not the parent)
mapped = any([e.mapped for e in upstream_states]) and map_index is None
task_inputs = {} # type: Dict[str, Any]
try:
# initialize the run
state, context = self.initialize_run(state, context)
# run state transformation pipeline
with prefect.context(context):
if prefect.context.get("task_loop_count") is None:
self.logger.info(
"Task '{name}': Starting task run...".format(
name=context["task_full_name"]
)
)
# check to make sure the task is in a pending state
state = self.check_task_is_ready(state)
# check if the task has reached its scheduled time
state = self.check_task_reached_start_time(state)
# Tasks never run if the upstream tasks haven't finished
state = self.check_upstream_finished(
state, upstream_states=upstream_states
)
# check if any upstream tasks skipped (and if we need to skip)
state = self.check_upstream_skipped(
state, upstream_states=upstream_states
)
# if the task is mapped, process the mapped children and exit
if mapped:
state = self.run_mapped_task(
state=state,
upstream_states=upstream_states,
context=context,
executor=executor,
)
state = self.wait_for_mapped_task(state=state, executor=executor)
self.logger.debug(
"Task '{name}': task has been mapped; ending run.".format(
name=context["task_full_name"]
)
)
raise ENDRUN(state)
# retrieve task inputs from upstream and also explicitly passed inputs
task_inputs = self.get_task_inputs(
state=state, upstream_states=upstream_states
)
# check to see if the task has a cached result
state = self.check_task_is_cached(state, inputs=task_inputs)
# check if the task's trigger passes
# triggers can raise Pauses, which require task_inputs to be available for caching
# so we run this after the previous step
state = self.check_task_trigger(state, upstream_states=upstream_states)
# set the task state to running
state = self.set_task_to_running(state)
# run the task
state = self.get_task_run_state(
state, inputs=task_inputs, timeout_handler=executor.timeout_handler
)
# cache the output, if appropriate
state = self.cache_result(state, inputs=task_inputs)
# check if the task needs to be retried
state = self.check_for_retry(state, inputs=task_inputs)
state = self.check_task_is_looping(
state,
inputs=task_inputs,
upstream_states=upstream_states,
context=context,
executor=executor,
)
# for pending signals, including retries and pauses we need to make sure the
# task_inputs are set
except (ENDRUN, signals.PrefectStateSignal) as exc:
if exc.state.is_pending() or exc.state.is_failed():
exc.state.cached_inputs = task_inputs or {} # type: ignore
state = exc.state
except RecursiveCall as exc:
raise exc
except Exception as exc:
msg = "Task '{name}': unexpected error while running task: {exc}".format(
name=context["task_full_name"], exc=repr(exc)
)
self.logger.exception(msg)
state = Failed(message=msg, result=exc)
if prefect.context.get("raise_on_exception"):
raise exc
# to prevent excessive repetition of this log
# since looping relies on recursively calling self.run
# TODO: figure out a way to only log this one single time instead of twice
if prefect.context.get("task_loop_count") is None:
# wrapping this final log in prefect.context(context) ensures
# that any run-context, including task-run-ids, are respected
with prefect.context(context):
self.logger.info(
"Task '{name}': finished task run for task with final state: '{state}'".format(
name=context["task_full_name"], state=type(state).__name__
)
)
return state
def call_runner_target_handlers(self, old_state: State,
new_state: State) -> State:
"""
A special state handler that the TaskRunner uses to call its task's state handlers.
This method is called as part of the base Runner's `handle_state_change()` method.
Args:
- old_state (State): the old (previous) state
- new_state (State): the new (current) state
Returns:
- State: the new state
"""
raise_on_exception = prefect.context.get("raise_on_exception", False)
try:
new_state = super().call_runner_target_handlers(
old_state=old_state, new_state=new_state)
# PrefectStateSignals are trapped and turned into States
except prefect.engine.signals.PrefectStateSignal as exc:
self.logger.info("{name} signal raised: {rep}".format(
name=type(exc).__name__, rep=repr(exc)))
if raise_on_exception:
raise exc
new_state = exc.state
except Exception as exc:
msg = "Exception raised while calling state handlers: {}".format(
repr(exc))
self.logger.exception(msg)
if raise_on_exception:
raise exc
new_state = Failed(msg, result=exc)
task_run_id = prefect.context.get("task_run_id")
version = prefect.context.get("task_run_version")
try:
cloud_state = new_state
state = self.client.set_task_run_state(
task_run_id=task_run_id,
version=version if cloud_state.is_running() else None,
state=cloud_state,
cache_for=self.task.cache_for,
)
except VersionLockError as exc:
state = self.client.get_task_run_state(task_run_id=task_run_id)
if state.is_running():
self.logger.debug(
"Version lock encountered and task {} is already in a running state."
.format(self.task.name))
raise ENDRUN(state=state) from exc
self.logger.debug(
"Version lock encountered for task {}, proceeding with state {}..."
.format(self.task.name,
type(state).__name__))
try:
new_state = state.load_result(self.result)
except Exception as exc_inner:
self.logger.debug(
"Error encountered attempting to load result for state of {} task..."
.format(self.task.name))
self.logger.error(repr(exc_inner))
raise ENDRUN(state=state) from exc_inner
except Exception as exc:
self.logger.exception(
"Failed to set task state with error: {}".format(repr(exc)))
raise ENDRUN(state=ClientFailed(state=new_state)) from exc
if state.is_queued():
state.state = old_state # type: ignore
raise ENDRUN(state=state)
prefect.context.update(task_run_version=(version or 0) + 1)
return new_state
def check_task_ready_to_map(
self, state: State, upstream_states: Dict[Edge, State]
) -> State:
"""
Checks if the parent task is ready to proceed with mapping.
Args:
- state (State): the current state of this task
- upstream_states (Dict[Edge, Union[State, List[State]]]): the upstream states
Raises:
- ENDRUN: either way, we dont continue past this point
"""
if state.is_mapped():
# this indicates we are executing a re-run of a mapped pipeline;
# in this case, we populate both `map_states` and `cached_inputs`
# to ensure the flow runner can properly regenerate the child tasks,
# regardless of whether we mapped over an exchanged piece of data
# or a non-data-exchanging upstream dependency
if len(state.map_states) == 0 and state.n_map_states > 0: # type: ignore
state.map_states = [None] * state.n_map_states # type: ignore
state.cached_inputs = {
edge.key: state._result # type: ignore
for edge, state in upstream_states.items()
if edge.key
}
raise ENDRUN(state)
# we can't map if there are no success states with iterables upstream
if upstream_states and not any(
[
edge.mapped and state.is_successful()
for edge, state in upstream_states.items()
]
):
new_state = Failed("No upstream states can be mapped over.") # type: State
raise ENDRUN(new_state)
elif not all(
[
hasattr(state.result, "__getitem__")
for edge, state in upstream_states.items()
if state.is_successful() and not state.is_mapped() and edge.mapped
]
):
new_state = Failed("At least one upstream state has an unmappable result.")
raise ENDRUN(new_state)
else:
# compute and set n_map_states
n_map_states = min(
[
len(s.result)
for e, s in upstream_states.items()
if e.mapped and s.is_successful() and not s.is_mapped()
]
+ [
s.n_map_states # type: ignore
for e, s in upstream_states.items()
if e.mapped and s.is_mapped()
],
default=0,
)
new_state = Mapped(
"Ready to proceed with mapping.", n_map_states=n_map_states
)
raise ENDRUN(new_state)
def get_flow_run_state(
self,
state: State,
task_states: Dict[Task, State],
task_contexts: Dict[Task, Dict[str, Any]],
return_tasks: Set[Task],
task_runner_state_handlers: Iterable[Callable],
executor: "prefect.executors.base.Executor",
) -> State:
"""
Runs the flow.
Args:
- state (State): starting state for the Flow. Defaults to
`Pending`
- task_states (dict): dictionary of task states to begin
computation with, with keys being Tasks and values their corresponding state
- task_contexts (Dict[Task, Dict[str, Any]]): contexts that will be provided to
each task
- return_tasks ([Task], optional): list of Tasks to include in the
final returned Flow state. Defaults to `None`
- task_runner_state_handlers (Iterable[Callable]): A list of state change handlers
that will be provided to the task_runner, and called whenever a task changes
state.
- executor (Executor): executor to use when performing computation; defaults to the
executor provided in your prefect configuration
Returns:
- State: `State` representing the final post-run state of the `Flow`.
"""
# this dictionary is used for tracking the states of "children" mapped tasks;
# when running on Dask, we want to avoid serializing futures, so instead
# of storing child task states in the `map_states` attribute we instead store
# in this dictionary and only after they are resolved do we attach them to the Mapped state
mapped_children = dict() # type: Dict[Task, list]
if not state.is_running():
self.logger.info("Flow is not in a Running state.")
raise ENDRUN(state)
if return_tasks is None:
return_tasks = set()
if set(return_tasks).difference(self.flow.tasks):
raise ValueError("Some tasks in return_tasks were not found in the flow.")
def extra_context(task: Task, task_index: int = None) -> dict:
return {
"task_name": task.name,
"task_tags": task.tags,
"task_index": task_index,
}
# -- process each task in order
with self.check_for_cancellation(), executor.start():
for task in self.flow.sorted_tasks():
task_state = task_states.get(task)
# if a task is a constant task, we already know its return value
# no need to use up resources by running it through a task runner
if task_state is None and isinstance(
task, prefect.tasks.core.constants.Constant
):
task_states[task] = task_state = Success(result=task.value)
# Always restart completed resource setup/cleanup tasks and
# secret tasks unless they were explicitly cached.
# TODO: we only need to rerun these tasks if any pending
# downstream tasks depend on them.
if (
isinstance(
task,
(
prefect.tasks.core.resource_manager.ResourceSetupTask,
prefect.tasks.core.resource_manager.ResourceCleanupTask,
prefect.tasks.secrets.SecretBase,
),
)
and task_state is not None
and task_state.is_finished()
and not task_state.is_cached()
):
task_states[task] = task_state = Pending()
# if the state is finished, don't run the task, just use the provided state if
# the state is cached / mapped, we still want to run the task runner pipeline
# steps to either ensure the cache is still valid / or to recreate the mapped
# pipeline for possible retries
if (
isinstance(task_state, State)
and task_state.is_finished()
and not task_state.is_cached()
and not task_state.is_mapped()
):
continue
upstream_states = {} # type: Dict[Edge, State]
# this dictionary is used exclusively for "reduce" tasks in particular we store
# the states / futures corresponding to the upstream children, and if running
# on Dask, let Dask resolve them at the appropriate time.
# Note: this is an optimization that allows Dask to resolve the mapped
# dependencies by "elevating" them to a function argument.
upstream_mapped_states = {} # type: Dict[Edge, list]
# -- process each edge to the task
for edge in self.flow.edges_to(task):
# load the upstream task states (supplying Pending as a default)
upstream_states[edge] = task_states.get(
edge.upstream_task, Pending(message="Task state not available.")
)
# if the edge is flattened and not the result of a map, then we
# preprocess the upstream states. If it IS the result of a
# map, it will be handled in `prepare_upstream_states_for_mapping`
if edge.flattened:
if not isinstance(upstream_states[edge], Mapped):
upstream_states[edge] = executor.submit(
executors.flatten_upstream_state, upstream_states[edge]
)
# this checks whether the task is a "reduce" task for a mapped pipeline
# and if so, collects the appropriate upstream children
if not edge.mapped and isinstance(upstream_states[edge], Mapped):
children = mapped_children.get(edge.upstream_task, [])
# if the edge is flattened, then we need to wait for the mapped children
# to complete and then flatten them
if edge.flattened:
children = executors.flatten_mapped_children(
mapped_children=children, executor=executor
)
upstream_mapped_states[edge] = children
# augment edges with upstream constants
for key, val in self.flow.constants[task].items():
edge = Edge(
upstream_task=prefect.tasks.core.constants.Constant(val),
downstream_task=task,
key=key,
)
upstream_states[edge] = Success(
"Auto-generated constant value",
result=ConstantResult(value=val),
)
# handle mapped tasks
if any(edge.mapped for edge in upstream_states.keys()):
# wait on upstream states to determine the width of the pipeline
# this is the key to depth-first execution
upstream_states = executor.wait(
{e: state for e, state in upstream_states.items()}
)
# we submit the task to the task runner to determine if
# we can proceed with mapping - if the new task state is not a Mapped
# state then we don't proceed
task_states[task] = executor.wait(
executor.submit(
run_task,
task=task,
state=task_state, # original state
upstream_states=upstream_states,
context=dict(
prefect.context, **task_contexts.get(task, {})
),
flow_result=self.flow.result,
task_runner_cls=self.task_runner_cls,
task_runner_state_handlers=task_runner_state_handlers,
upstream_mapped_states=upstream_mapped_states,
is_mapped_parent=True,
extra_context=extra_context(task),
)
)
# either way, we should now have enough resolved states to restructure
# the upstream states into a list of upstream state dictionaries to iterate over
list_of_upstream_states = (
executors.prepare_upstream_states_for_mapping(
task_states[task],
upstream_states,
mapped_children,
executor=executor,
)
)
submitted_states = []
for idx, states in enumerate(list_of_upstream_states):
# if we are on a future rerun of a partially complete flow run,
# there might be mapped children in a retrying state; this check
# looks into the current task state's map_states for such info
if (
isinstance(task_state, Mapped)
and len(task_state.map_states) >= idx + 1
):
current_state = task_state.map_states[
idx
] # type: Optional[State]
elif isinstance(task_state, Mapped):
current_state = None
else:
current_state = task_state
# this is where each child is submitted for actual work
submitted_states.append(
executor.submit(
run_task,
task=task,
state=current_state,
upstream_states=states,
context=dict(
prefect.context,
**task_contexts.get(task, {}),
map_index=idx,
),
flow_result=self.flow.result,
task_runner_cls=self.task_runner_cls,
task_runner_state_handlers=task_runner_state_handlers,
upstream_mapped_states=upstream_mapped_states,
extra_context=extra_context(task, task_index=idx),
)
)
if isinstance(task_states.get(task), Mapped):
mapped_children[task] = submitted_states # type: ignore
else:
task_states[task] = executor.submit(
run_task,
task=task,
state=task_state,
upstream_states=upstream_states,
context=dict(prefect.context, **task_contexts.get(task, {})),
flow_result=self.flow.result,
task_runner_cls=self.task_runner_cls,
task_runner_state_handlers=task_runner_state_handlers,
upstream_mapped_states=upstream_mapped_states,
extra_context=extra_context(task),
)
# ---------------------------------------------
# Collect results
# ---------------------------------------------
# terminal tasks determine if the flow is finished
terminal_tasks = self.flow.terminal_tasks()
# reference tasks determine flow state
reference_tasks = self.flow.reference_tasks()
# wait until all terminal tasks are finished
final_tasks = terminal_tasks.union(reference_tasks).union(return_tasks)
final_states = executor.wait(
{
t: task_states.get(t, Pending("Task not evaluated by FlowRunner."))
for t in final_tasks
}
)
# also wait for any children of Mapped tasks to finish, and add them
# to the dictionary to determine flow state
all_final_states = final_states.copy()
for t, s in list(final_states.items()):
if s.is_mapped():
# ensure we wait for any mapped children to complete
if t in mapped_children:
s.map_states = executor.wait(mapped_children[t])
s.result = [ms.result for ms in s.map_states]
all_final_states[t] = s.map_states
assert isinstance(final_states, dict)
key_states = set(flatten_seq([all_final_states[t] for t in reference_tasks]))
terminal_states = set(
flatten_seq([all_final_states[t] for t in terminal_tasks])
)
return_states = {t: final_states[t] for t in return_tasks}
state = self.determine_final_state(
state=state,
key_states=key_states,
return_states=return_states,
terminal_states=terminal_states,
)
return state
def get_task_run_state(
self,
state: State,
inputs: Dict[str, Result],
timeout_handler: Optional[Callable] = None,
) -> State:
"""
Runs the task and traps any signals or errors it raises.
Also checkpoints the result of a successful task, if `task.checkpoint` is `True`.
Args:
- state (State): the current state of this task
- inputs (Dict[str, Result], optional): a dictionary of inputs whose keys correspond
to the task's `run()` arguments.
- timeout_handler (Callable, optional): function for timing out
task execution, with call signature `handler(fn, *args, **kwargs)`. Defaults to
`prefect.utilities.executors.timeout_handler`
Returns:
- State: the state of the task after running the check
Raises:
- signals.PAUSE: if the task raises PAUSE
- ENDRUN: if the task is not ready to run
"""
if not state.is_running():
self.logger.debug(
"Task '{name}': can't run task because it's not in a "
"Running state; ending run.".format(name=prefect.context.get(
"task_full_name", self.task.name)))
raise ENDRUN(state)
try:
self.logger.debug(
"Task '{name}': Calling task.run() method...".format(
name=prefect.context.get("task_full_name",
self.task.name)))
timeout_handler = (timeout_handler
or prefect.utilities.executors.timeout_handler)
raw_inputs = {k: r.value for k, r in inputs.items()}
if getattr(self.task, "log_stdout", False):
with redirect_stdout(
prefect.utilities.logging.RedirectToLog(
self.logger)): # type: ignore
result = timeout_handler(self.task.run,
timeout=self.task.timeout,
**raw_inputs)
else:
result = timeout_handler(self.task.run,
timeout=self.task.timeout,
**raw_inputs)
except KeyboardInterrupt:
self.logger.debug("Interrupt signal raised, cancelling task run.")
state = Cancelled(
message="Interrupt signal raised, cancelling task run.")
return state
# inform user of timeout
except TimeoutError as exc:
if prefect.context.get("raise_on_exception"):
raise exc
state = TimedOut("Task timed out during execution.",
result=exc,
cached_inputs=inputs)
return state
except signals.LOOP as exc:
new_state = exc.state
assert isinstance(new_state, Looped)
new_state.result = Result(value=new_state.result,
result_handler=self.result_handler)
new_state.cached_inputs = inputs
new_state.message = exc.state.message or "Task is looping ({})".format(
new_state.loop_count)
return new_state
result = Result(value=result, result_handler=self.result_handler)
state = Success(result=result,
message="Task run succeeded.",
cached_inputs=inputs)
## checkpoint tasks if a result_handler is present, except for when the user has opted out by disabling checkpointing
if (state.is_successful()
and prefect.context.get("checkpointing") is True
and self.task.checkpoint is not False
and self.result_handler is not None):
state._result.store_safe_value()
return state
def get_task_run_state(self, state: State, inputs: Dict[str,
Result]) -> State:
"""
Runs the task and traps any signals or errors it raises.
Also checkpoints the result of a successful task, if `task.checkpoint` is `True`.
Args:
- state (State): the current state of this task
- inputs (Dict[str, Result], optional): a dictionary of inputs whose keys correspond
to the task's `run()` arguments.
Returns:
- State: the state of the task after running the check
Raises:
- signals.PAUSE: if the task raises PAUSE
- ENDRUN: if the task is not ready to run
"""
if not state.is_running():
self.logger.debug(
"Task '{name}': can't run task because it's not in a "
"Running state; ending run.".format(name=prefect.context.get(
"task_full_name", self.task.name)))
raise ENDRUN(state)
value = None
raw_inputs = {k: r.value for k, r in inputs.items()}
try:
self.logger.debug(
"Task '{name}': Calling task.run() method...".format(
name=prefect.context.get("task_full_name",
self.task.name)))
timeout_handler = prefect.utilities.executors.timeout_handler
if getattr(self.task, "log_stdout", False):
with redirect_stdout(
prefect.utilities.logging.RedirectToLog(
self.logger) # type: ignore
):
value = timeout_handler(self.task.run,
timeout=self.task.timeout,
**raw_inputs)
else:
value = timeout_handler(self.task.run,
timeout=self.task.timeout,
**raw_inputs)
# inform user of timeout
except TimeoutError as exc:
if prefect.context.get("raise_on_exception"):
raise exc
state = TimedOut("Task timed out during execution.", result=exc)
return state
except signals.LOOP as exc:
new_state = exc.state
assert isinstance(new_state, Looped)
new_state.result = self.result.from_value(value=new_state.result)
new_state.message = exc.state.message or "Task is looping ({})".format(
new_state.loop_count)
return new_state
# checkpoint tasks if a result is present, except for when the user has opted out by
# disabling checkpointing
if (prefect.context.get("checkpointing") is True
and self.task.checkpoint is not False and value is not None):
try:
formatting_kwargs = {
**prefect.context.get("parameters", {}).copy(),
**raw_inputs,
**prefect.context,
}
result = self.result.write(value, **formatting_kwargs)
except NotImplementedError:
result = self.result.from_value(value=value)
else:
result = self.result.from_value(value=value)
state = Success(result=result, message="Task run succeeded.")
return state
def check_task_is_ready(self, state: State) -> State:
"""
Checks to make sure the task is ready to run (Pending or Mapped).
If the state is Paused, an ENDRUN is raised.
Args:
- state (State): the current state of this task
Returns:
- State: the state of the task after running the check
Raises:
- ENDRUN: if the task is not ready to run
"""
# the task is paused
if isinstance(state, Paused):
self.logger.debug(
"Task '{name}': task is paused; ending run.".format(
name=prefect.context.get("task_full_name", self.task.name)
)
)
raise ENDRUN(state)
# the task is ready
elif state.is_pending():
return state
# the task is mapped, in which case we still proceed so that the children tasks
# are generated (note that if the children tasks)
elif state.is_mapped():
self.logger.debug(
"Task '{name}': task is mapped, but run will proceed so children are generated.".format(
name=prefect.context.get("task_full_name", self.task.name)
)
)
return state
# this task is already running
elif state.is_running():
self.logger.debug(
"Task '{name}': task is already running.".format(
name=prefect.context.get("task_full_name", self.task.name)
)
)
raise ENDRUN(state)
elif state.is_cached():
return state
# this task is already finished
elif state.is_finished():
self.logger.debug(
"Task '{name}': task is already finished.".format(
name=prefect.context.get("task_full_name", self.task.name)
)
)
raise ENDRUN(state)
# this task is not pending
else:
self.logger.debug(
"Task '{name}' is not ready to run or state was unrecognized ({state}).".format(
name=prefect.context.get("task_full_name", self.task.name),
state=state,
)
)
raise ENDRUN(state)
def call_runner_target_handlers(self, old_state: State, new_state: State) -> State:
"""
A special state handler that the FlowRunner uses to call its flow's state handlers.
This method is called as part of the base Runner's `handle_state_change()` method.
Args:
- old_state (State): the old (previous) state
- new_state (State): the new (current) state
Returns:
- State: the new state
"""
raise_on_exception = prefect.context.get("raise_on_exception", False)
try:
new_state = super().call_runner_target_handlers(
old_state=old_state, new_state=new_state
)
except Exception as exc:
msg = "Exception raised while calling state handlers: {}".format(repr(exc))
self.logger.exception(msg)
if raise_on_exception:
raise exc
new_state = Failed(msg, result=exc)
flow_run_id = prefect.context.get("flow_run_id", None)
version = prefect.context.get("flow_run_version")
try:
cloud_state = new_state
state = self.client.set_flow_run_state(
flow_run_id=flow_run_id,
version=version if cloud_state.is_running() else None,
state=cloud_state,
)
except VersionLockError as exc:
state = self.client.get_flow_run_state(flow_run_id=flow_run_id)
if state.is_running():
self.logger.debug(
"Version lock encountered and flow is already in a running state."
)
raise ENDRUN(state=state) from exc
self.logger.debug(
"Version lock encountered, proceeding with state {}...".format(
type(state).__name__
)
)
new_state = state
except Exception as exc:
self.logger.exception(
"Failed to set flow state with error: {}".format(repr(exc))
)
raise ENDRUN(state=new_state) from exc
if state.is_queued():
state.state = old_state # type: ignore
raise ENDRUN(state=state)
prefect.context.update(flow_run_version=(version or 0) + 1)
return new_state
def initialize_run( # type: ignore
self,
state: Optional[State],
task_states: Dict[Task, State],
context: Dict[str, Any],
task_contexts: Dict[Task, Dict[str, Any]],
parameters: Dict[str, Any],
) -> FlowRunnerInitializeResult:
"""
Initializes the Task run by initializing state and context appropriately.
If the provided state is a Submitted state, the state it wraps is extracted.
Args:
- state (Optional[State]): the initial state of the run
- task_states (Dict[Task, State]): a dictionary of any initial task states
- context (Dict[str, Any], optional): prefect.Context to use for execution
to use for each Task run
- task_contexts (Dict[Task, Dict[str, Any]], optional): contexts that will be
provided to each task
- parameters(dict): the parameter values for the run
Returns:
- NamedTuple: a tuple of initialized objects:
`(state, task_states, context, task_contexts)`
"""
# load id from context
flow_run_id = prefect.context.get("flow_run_id")
try:
flow_run_info = self.client.get_flow_run_info(flow_run_id)
except Exception as exc:
self.logger.debug(
"Failed to retrieve flow state with error: {}".format(repr(exc))
)
if state is None:
state = Failed(
message="Could not retrieve state from Prefect Cloud", result=exc
)
raise ENDRUN(state=state) from exc
updated_context = context or {}
updated_context.update(flow_run_info.context or {})
updated_context.update(
flow_id=flow_run_info.flow_id,
flow_run_id=flow_run_info.id,
flow_run_version=flow_run_info.version,
flow_run_name=flow_run_info.name,
scheduled_start_time=flow_run_info.scheduled_start_time,
)
tasks = {slug: t for t, slug in self.flow.slugs.items()}
# update task states and contexts
for task_run in flow_run_info.task_runs:
try:
task = tasks[task_run.task_slug]
except KeyError as exc:
msg = (
f"Task slug {task_run.task_slug} not found in the current Flow; "
f"this is usually caused by changing the Flow without reregistering "
f"it with the Prefect API."
)
raise KeyError(msg) from exc
task_states.setdefault(task, task_run.state)
task_contexts.setdefault(task, {}).update(
task_id=task_run.task_id,
task_run_id=task_run.id,
task_run_version=task_run.version,
)
# if state is set, keep it; otherwise load from Cloud
state = state or flow_run_info.state # type: ignore
# update parameters, prioritizing kwarg-provided params
updated_parameters = flow_run_info.parameters or {} # type: ignore
updated_parameters.update(parameters)
return super().initialize_run(
state=state,
task_states=task_states,
context=updated_context,
task_contexts=task_contexts,
parameters=updated_parameters,
)
def check_for_cancellation(self) -> Iterator:
"""Contextmanager used to wrap a cancellable section of a flow run."""
cancelling = False
done = threading.Event()
flow_run_version = None
context = prefect.context.to_dict()
def interrupt_if_cancelling() -> None:
# We need to copy the context into this thread, since context is a
# thread local.
with prefect.context(context):
flow_run_id = prefect.context["flow_run_id"]
while True:
exiting_context = done.wait(
prefect.config.cloud.check_cancellation_interval
)
try:
self.logger.debug("Checking flow run state...")
flow_run_info = self.client.get_flow_run_info(flow_run_id)
except Exception:
self.logger.warning(
"Error getting flow run info", exc_info=True
)
continue
if not flow_run_info.state.is_running():
self.logger.warning(
"Flow run is no longer in a running state; the current state is: %r",
flow_run_info.state,
)
if isinstance(flow_run_info.state, Cancelling):
self.logger.info(
"Flow run has been cancelled, cancelling active tasks"
)
nonlocal cancelling
nonlocal flow_run_version
cancelling = True
flow_run_version = flow_run_info.version
# If not already leaving context, raise KeyboardInterrupt in the main thread
if not exiting_context:
if hasattr(signal, "raise_signal"):
# New in python 3.8
signal.raise_signal(signal.SIGINT) # type: ignore
else:
if os.name == "nt":
# This doesn't actually send a signal, so it will only
# interrupt the next Python bytecode instruction - if the
# main thread is blocked in a c extension the interrupt
# won't be seen until that returns.
from _thread import interrupt_main
interrupt_main()
else:
signal.pthread_kill(
threading.main_thread().ident, signal.SIGINT # type: ignore
)
break
elif exiting_context:
break
thread = threading.Thread(target=interrupt_if_cancelling, daemon=True)
thread.start()
try:
yield
except KeyboardInterrupt:
if not cancelling:
raise
finally:
done.set()
thread.join()
if cancelling:
prefect.context.update(flow_run_version=flow_run_version)
raise ENDRUN(state=Cancelled("Flow run is cancelled"))
def get_flow_run_state(
self,
state: State,
task_states: Dict[Task, State],
task_contexts: Dict[Task, Dict[str, Any]],
return_tasks: Set[Task],
task_runner_state_handlers: Iterable[Callable],
executor: "prefect.engine.executors.base.Executor",
) -> State:
"""
Runs the flow.
Args:
- state (State): starting state for the Flow. Defaults to
`Pending`
- task_states (dict): dictionary of task states to begin
computation with, with keys being Tasks and values their corresponding state
- task_contexts (Dict[Task, Dict[str, Any]]): contexts that will be provided to each task
- return_tasks ([Task], optional): list of Tasks to include in the
final returned Flow state. Defaults to `None`
- task_runner_state_handlers (Iterable[Callable]): A list of state change
handlers that will be provided to the task_runner, and called whenever a task changes
state.
- executor (Executor): executor to use when performing
computation; defaults to the executor provided in your prefect configuration
Returns:
- State: `State` representing the final post-run state of the `Flow`.
"""
if not state.is_running():
self.logger.info("Flow is not in a Running state.")
raise ENDRUN(state)
if return_tasks is None:
return_tasks = set()
if set(return_tasks).difference(self.flow.tasks):
raise ValueError(
"Some tasks in return_tasks were not found in the flow.")
# -- process each task in order
with executor.start():
for task in self.flow.sorted_tasks():
task_state = task_states.get(task)
if task_state is None and isinstance(
task, prefect.tasks.core.constants.Constant):
task_states[task] = task_state = Success(result=task.value)
# if the state is finished, don't run the task, just use the provided state
if (isinstance(task_state, State) and task_state.is_finished()
and not task_state.is_cached()
and not task_state.is_mapped()):
continue
upstream_states = {
} # type: Dict[Edge, Union[State, Iterable]]
# -- process each edge to the task
for edge in self.flow.edges_to(task):
upstream_states[edge] = task_states.get(
edge.upstream_task,
Pending(message="Task state not available."))
# -- run the task
with prefect.context(task_full_name=task.name,
task_tags=task.tags):
task_states[task] = executor.submit(
self.run_task,
task=task,
state=task_state,
upstream_states=upstream_states,
context=dict(prefect.context,
**task_contexts.get(task, {})),
task_runner_state_handlers=task_runner_state_handlers,
executor=executor,
)
# ---------------------------------------------
# Collect results
# ---------------------------------------------
# terminal tasks determine if the flow is finished
terminal_tasks = self.flow.terminal_tasks()
# reference tasks determine flow state
reference_tasks = self.flow.reference_tasks()
# wait until all terminal tasks are finished
final_tasks = terminal_tasks.union(reference_tasks).union(
return_tasks)
final_states = executor.wait({
t:
task_states.get(t,
Pending("Task not evaluated by FlowRunner."))
for t in final_tasks
})
# also wait for any children of Mapped tasks to finish, and add them
# to the dictionary to determine flow state
all_final_states = final_states.copy()
for t, s in list(final_states.items()):
if s.is_mapped():
s.map_states = executor.wait(s.map_states)
s.result = [ms.result for ms in s.map_states]
all_final_states[t] = s.map_states
assert isinstance(final_states, dict)
key_states = set(
flatten_seq([all_final_states[t] for t in reference_tasks]))
terminal_states = set(
flatten_seq([all_final_states[t] for t in terminal_tasks]))
return_states = {t: final_states[t] for t in return_tasks}
state = self.determine_final_state(
state=state,
key_states=key_states,
return_states=return_states,
terminal_states=terminal_states,
)
return state
