Source code for taskflow.engines.action_engine.engine

# -*- coding: utf-8 -*-

#    Copyright (C) 2012 Yahoo! Inc. All Rights Reserved.
#    Licensed under the Apache License, Version 2.0 (the "License"); you may
#    not use this file except in compliance with the License. You may obtain
#    a copy of the License at
#    Unless required by applicable law or agreed to in writing, software
#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
#    License for the specific language governing permissions and limitations
#    under the License.

import collections
import contextlib
import itertools
import threading

from automaton import runners
from concurrent import futures
import fasteners
import functools
import networkx as nx
from oslo_utils import excutils
from oslo_utils import strutils
from oslo_utils import timeutils

from taskflow.engines.action_engine import builder
from taskflow.engines.action_engine import compiler
from taskflow.engines.action_engine import executor
from taskflow.engines.action_engine import process_executor
from taskflow.engines.action_engine import runtime
from taskflow.engines import base
from taskflow import exceptions as exc
from taskflow import logging
from taskflow import states
from taskflow import storage
from taskflow.types import failure
from taskflow.utils import misc

LOG = logging.getLogger(__name__)

def _start_stop(task_executor, retry_executor):
    # A teenie helper context manager to safely start/stop engine executors...
            yield (task_executor, retry_executor)

def _pre_check(check_compiled=True, check_storage_ensured=True,
    """Engine state precondition checking decorator."""

    def decorator(meth):
        do_what = meth.__name__

        def wrapper(self, *args, **kwargs):
            if check_compiled and not self._compiled:
                raise exc.InvalidState("Can not %s an engine which"
                                       " has not been compiled" % do_what)
            if check_storage_ensured and not self._storage_ensured:
                raise exc.InvalidState("Can not %s an engine"
                                       " which has not had its storage"
                                       " populated" % do_what)
            if check_validated and not self._validated:
                raise exc.InvalidState("Can not %s an engine which"
                                       " has not been validated" % do_what)
            return meth(self, *args, **kwargs)

        return wrapper

    return decorator

[docs]class ActionEngine(base.Engine): """Generic action-based engine. This engine compiles the flow (and any subflows) into a compilation unit which contains the full runtime definition to be executed and then uses this compilation unit in combination with the executor, runtime, machine builder and storage classes to attempt to run your flow (and any subflows & contained atoms) to completion. NOTE(harlowja): during this process it is permissible and valid to have a task or multiple tasks in the execution graph fail (at the same time even), which will cause the process of reversion or retrying to commence. See the valid states in the states module to learn more about what other states the tasks and flow being ran can go through. **Engine options:** +----------------------+-----------------------+------+------------+ | Name/key | Description | Type | Default | +======================+=======================+======+============+ | ``defer_reverts`` | This option lets you | bool | ``False`` | | | safely nest flows | | | | | with retries inside | | | | | flows without retries | | | | | and it still behaves | | | | | as a user would | | | | | expect (for example | | | | | if the retry gets | | | | | exhausted it reverts | | | | | the outer flow unless | | | | | the outer flow has a | | | | | has a separate retry | | | | | behavior). | | | +----------------------+-----------------------+------+------------+ | ``never_resolve`` | When true, instead | bool | ``False`` | | | of reverting | | | | | and trying to resolve | | | | | a atom failure the | | | | | engine will skip | | | | | reverting and abort | | | | | instead of reverting | | | | | and/or retrying. | | | +----------------------+-----------------------+------+------------+ | ``inject_transient`` | When true, values | bool | ``True`` | | | that are local to | | | | | each atoms scope | | | | | are injected into | | | | | storage into a | | | | | transient location | | | | | (typically a local | | | | | dictionary), when | | | | | false those values | | | | | are instead persisted | | | | | into atom details | | | | | (and saved in a non- | | | | | transient manner). | | | +----------------------+-----------------------+------+------------+ """ NO_RERAISING_STATES = frozenset([states.SUSPENDED, states.SUCCESS]) """ States that if the engine stops in will **not** cause any potential failures to be reraised. States **not** in this list will cause any failure/s that were captured (if any) to get reraised. """ IGNORABLE_STATES = frozenset( itertools.chain([states.SCHEDULING, states.WAITING, states.RESUMING, states.ANALYZING], builder.META_STATES)) """ Informational states this engines internal machine yields back while running, not useful to have the engine record but useful to provide to end-users when doing execution iterations via :py:meth:`.run_iter`. """ MAX_MACHINE_STATES_RETAINED = 10 """ During :py:meth:`~.run_iter` the last X state machine transitions will be recorded (typically only useful on failure). """ def __init__(self, flow, flow_detail, backend, options): super(ActionEngine, self).__init__(flow, flow_detail, backend, options) self._runtime = None self._compiled = False self._compilation = None self._compiler = compiler.PatternCompiler(flow) self._lock = threading.RLock() self._storage_ensured = False self._validated = False # Retries are not *currently* executed out of the engines process # or thread (this could change in the future if we desire it to). self._retry_executor = executor.SerialRetryExecutor() self._inject_transient = strutils.bool_from_string( self._options.get('inject_transient', True)) self._gather_statistics = strutils.bool_from_string( self._options.get('gather_statistics', True)) self._statistics = {}
[docs] @_pre_check(check_compiled=True, # NOTE(harlowja): We can alter the state of the # flow without ensuring its storage is setup for # its atoms (since this state change does not affect # those units). check_storage_ensured=False, check_validated=False) def suspend(self): self._change_state(states.SUSPENDING)
@property def statistics(self): return self._statistics @property def compilation(self): """The compilation result. NOTE(harlowja): Only accessible after compilation has completed (None will be returned when this property is accessed before compilation has completed successfully). """ if self._compiled: return self._compilation else: return None @misc.cachedproperty def storage(self): """The storage unit for this engine. NOTE(harlowja): the atom argument lookup strategy will change for this storage unit after :py:func:`~taskflow.engines.base.Engine.compile` has completed (since **only** after compilation is the actual structure known). Before :py:func:`~taskflow.engines.base.Engine.compile` has completed the atom argument lookup strategy lookup will be restricted to injected arguments **only** (this will **not** reflect the actual runtime lookup strategy, which typically will be, but is not always different). """ def _scope_fetcher(atom_name): if self._compiled: return self._runtime.fetch_scopes_for(atom_name) else: return None return storage.Storage(self._flow_detail, backend=self._backend, scope_fetcher=_scope_fetcher)
[docs] def run(self, timeout=None): """Runs the engine (or die trying). :param timeout: timeout to wait for any atoms to complete (this timeout will be used during the waiting period that occurs when unfinished atoms are being waited on). """ with fasteners.try_lock(self._lock) as was_locked: if not was_locked: raise exc.ExecutionFailure("Engine currently locked, please" " try again later") for _state in self.run_iter(timeout=timeout): pass
[docs] def run_iter(self, timeout=None): """Runs the engine using iteration (or die trying). :param timeout: timeout to wait for any atoms to complete (this timeout will be used during the waiting period that occurs after the waiting state is yielded when unfinished atoms are being waited on). Instead of running to completion in a blocking manner, this will return a generator which will yield back the various states that the engine is going through (and can be used to run multiple engines at once using a generator per engine). The iterator returned also responds to the ``send()`` method from :pep:`0342` and will attempt to suspend itself if a truthy value is sent in (the suspend may be delayed until all active atoms have finished). NOTE(harlowja): using the ``run_iter`` method will **not** retain the engine lock while executing so the user should ensure that there is only one entity using a returned engine iterator (one per engine) at a given time. """ self.compile() self.prepare() self.validate() # Keep track of the last X state changes, which if a failure happens # are quite useful to log (and the performance of tracking this # should be negligible). last_transitions = collections.deque( maxlen=max(1, self.MAX_MACHINE_STATES_RETAINED)) with _start_stop(self._task_executor, self._retry_executor): self._change_state(states.RUNNING) if self._gather_statistics: self._statistics.clear() w = timeutils.StopWatch() w.start() else: w = None try: closed = False machine, memory = self._statistics, timeout=timeout, gather_statistics=self._gather_statistics) r = runners.FiniteRunner(machine) for transition in r.run_iter(builder.START): last_transitions.append(transition) _prior_state, new_state = transition # NOTE(harlowja): skip over meta-states if new_state in builder.META_STATES: continue if new_state == states.FAILURE: failure.Failure.reraise_if_any(memory.failures) if closed: continue try: try_suspend = yield new_state except GeneratorExit: # The generator was closed, attempt to suspend and # continue looping until we have cleanly closed up # shop... closed = True self.suspend() except Exception: # Capture the failure, and ensure that the # machine will notice that something externally # has sent an exception in and that it should # finish up and reraise. memory.failures.append(failure.Failure()) closed = True else: if try_suspend: self.suspend() except Exception: with excutils.save_and_reraise_exception(): LOG.exception("Engine execution has failed, something" " bad must have happened (last" " %s machine transitions were %s)", last_transitions.maxlen, list(last_transitions)) self._change_state(states.FAILURE) else: if last_transitions: _prior_state, new_state = last_transitions[-1] if new_state not in self.IGNORABLE_STATES: self._change_state(new_state) if new_state not in self.NO_RERAISING_STATES: e_failures = r_failures = er_failures = itertools.chain( e_failures.values(), r_failures.values()) failure.Failure.reraise_if_any(er_failures) finally: if w is not None: w.stop() self._statistics['active_for'] = w.elapsed()
@staticmethod def _check_compilation(compilation): """Performs post compilation validation/checks.""" seen = set() dups = set() execution_graph = compilation.execution_graph for node, node_attrs in execution_graph.nodes(data=True): if node_attrs['kind'] in compiler.ATOMS: atom_name = if atom_name in seen: dups.add(atom_name) else: seen.add(atom_name) if dups: raise exc.Duplicate( "Atoms with duplicate names found: %s" % (sorted(dups))) return compilation def _change_state(self, state): moved, old_state = if moved: details = { 'engine': self, 'flow_name':, 'flow_uuid':, 'old_state': old_state, } self.notifier.notify(state, details) def _ensure_storage(self): """Ensure all contained atoms exist in the storage unit.""" self._runtime.iterate_nodes(compiler.ATOMS)) for atom in self._runtime.iterate_nodes(compiler.ATOMS): if atom.inject:, atom.inject, transient=self._inject_transient)
[docs] @fasteners.locked @_pre_check(check_validated=False) def validate(self): # At this point we can check to ensure all dependencies are either # flow/task provided or storage provided, if there are still missing # dependencies then this flow will fail at runtime (which we can avoid # by failing at validation time). if LOG.isEnabledFor(logging.TRACE): execution_graph = self._compilation.execution_graph LOG.trace("Validating scoping and argument visibility for" " execution graph with %s nodes and %s edges with" " density %0.3f", execution_graph.number_of_nodes(), execution_graph.number_of_edges(), nx.density(execution_graph)) missing = set() # Attempt to retain a chain of what was missing (so that the final # raised exception for the flow has the nodes that had missing # dependencies). last_cause = None last_node = None missing_nodes = 0 for atom in self._runtime.iterate_nodes(compiler.ATOMS): exec_missing =, atom.rebind, optional_args=atom.optional) revert_missing =, atom.revert_rebind, optional_args=atom.revert_optional) atom_missing = (('execute', exec_missing), ('revert', revert_missing)) for method, method_missing in atom_missing: if method_missing: cause = exc.MissingDependencies(atom, sorted(method_missing), cause=last_cause, method=method) last_cause = cause last_node = atom missing_nodes += 1 missing.update(method_missing) if missing: # For when a task is provided (instead of a flow) and that # task is the only item in the graph and its missing deps, avoid # re-wrapping it in yet another exception... if missing_nodes == 1 and last_node is self._flow: raise last_cause else: raise exc.MissingDependencies(self._flow, sorted(missing), cause=last_cause) self._validated = True
[docs] @fasteners.locked @_pre_check(check_storage_ensured=False, check_validated=False) def prepare(self): if not self._storage_ensured: # Set our own state to resuming -> (ensure atoms exist # in storage) -> suspended in the storage unit and notify any # attached listeners of these changes. self._change_state(states.RESUMING) self._ensure_storage() self._change_state(states.SUSPENDED) self._storage_ensured = True # Reset everything back to pending (if we were previously reverted). if == states.REVERTED: self.reset()
[docs] @fasteners.locked @_pre_check(check_validated=False) def reset(self): # This transitions *all* contained atoms back into the PENDING state # with an intention to EXECUTE (or dies trying to do that) and then # changes the state of the flow to PENDING so that it can then run... self._runtime.reset_all() self._change_state(states.PENDING)
[docs] @fasteners.locked def compile(self): if self._compiled: return self._compilation = self._check_compilation(self._compiler.compile()) self._runtime = runtime.Runtime(self._compilation,, self.atom_notifier, self._task_executor, self._retry_executor, options=self._options) self._runtime.compile() self._compiled = True
[docs]class SerialActionEngine(ActionEngine): """Engine that runs tasks in serial manner.""" def __init__(self, flow, flow_detail, backend, options): super(SerialActionEngine, self).__init__(flow, flow_detail, backend, options) self._task_executor = executor.SerialTaskExecutor()
class _ExecutorTypeMatch(collections.namedtuple('_ExecutorTypeMatch', ['types', 'executor_cls'])): def matches(self, executor): return isinstance(executor, self.types) class _ExecutorTextMatch(collections.namedtuple('_ExecutorTextMatch', ['strings', 'executor_cls'])): def matches(self, text): return text.lower() in self.strings
[docs]class ParallelActionEngine(ActionEngine): """Engine that runs tasks in parallel manner. **Additional engine options:** * ``executor``: a object that implements a :pep:`3148` compatible executor interface; it will be used for scheduling tasks. The following type are applicable (other unknown types passed will cause a type error to be raised). ========================= =============================================== Type provided Executor used ========================= =============================================== |cft|.ThreadPoolExecutor :class:`~.executor.ParallelThreadTaskExecutor` |cfp|.ProcessPoolExecutor :class:`~.|pe|.ParallelProcessTaskExecutor` |cf|._base.Executor :class:`~.executor.ParallelThreadTaskExecutor` ========================= =============================================== * ``executor``: a string that will be used to select a :pep:`3148` compatible executor; it will be used for scheduling tasks. The following string are applicable (other unknown strings passed will cause a value error to be raised). =========================== =============================================== String (case insensitive) Executor used =========================== =============================================== ``process`` :class:`~.|pe|.ParallelProcessTaskExecutor` ``processes`` :class:`~.|pe|.ParallelProcessTaskExecutor` ``thread`` :class:`~.executor.ParallelThreadTaskExecutor` ``threaded`` :class:`~.executor.ParallelThreadTaskExecutor` ``threads`` :class:`~.executor.ParallelThreadTaskExecutor` ``greenthread`` :class:`~.executor.ParallelThreadTaskExecutor` (greened version) ``greedthreaded`` :class:`~.executor.ParallelThreadTaskExecutor` (greened version) ``greenthreads`` :class:`~.executor.ParallelThreadTaskExecutor` (greened version) =========================== =============================================== * ``max_workers``: a integer that will affect the number of parallel workers that are used to dispatch tasks into (this number is bounded by the maximum parallelization your workflow can support). * ``wait_timeout``: a float (in seconds) that will affect the parallel process task executor (and therefore is **only** applicable when the executor provided above is of the process variant). This number affects how much time the process task executor waits for messages from child processes (typically indicating they have finished or failed). A lower number will have high granularity but *currently* involves more polling while a higher number will involve less polling but a slower time for an engine to notice a task has completed. .. |pe| replace:: process_executor .. |cfp| replace:: concurrent.futures.process .. |cft| replace:: concurrent.futures.thread .. |cf| replace:: concurrent.futures """ # One of these types should match when a object (non-string) is provided # for the 'executor' option. # # NOTE(harlowja): the reason we use the library/built-in futures is to # allow for instances of that to be detected and handled correctly, instead # of forcing everyone to use our derivatives (futurist or other)... _executor_cls_matchers = [ _ExecutorTypeMatch((futures.ThreadPoolExecutor,), executor.ParallelThreadTaskExecutor), _ExecutorTypeMatch((futures.ProcessPoolExecutor,), process_executor.ParallelProcessTaskExecutor), _ExecutorTypeMatch((futures.Executor,), executor.ParallelThreadTaskExecutor), ] # One of these should match when a string/text is provided for the # 'executor' option (a mixed case equivalent is allowed since the match # will be lower-cased before checking). _executor_str_matchers = [ _ExecutorTextMatch(frozenset(['processes', 'process']), process_executor.ParallelProcessTaskExecutor), _ExecutorTextMatch(frozenset(['thread', 'threads', 'threaded']), executor.ParallelThreadTaskExecutor), _ExecutorTextMatch(frozenset(['greenthread', 'greenthreads', 'greenthreaded']), executor.ParallelGreenThreadTaskExecutor), ] # Used when no executor is provided (either a string or object)... _default_executor_cls = executor.ParallelThreadTaskExecutor def __init__(self, flow, flow_detail, backend, options): super(ParallelActionEngine, self).__init__(flow, flow_detail, backend, options) # This ensures that any provided executor will be validated before # we get to far in the compilation/execution pipeline... self._task_executor = self._fetch_task_executor(self._options) @classmethod def _fetch_task_executor(cls, options): kwargs = {} executor_cls = cls._default_executor_cls # Match the desired executor to a class that will work with it... desired_executor = options.get('executor') if isinstance(desired_executor, str): matched_executor_cls = None for m in cls._executor_str_matchers: if m.matches(desired_executor): matched_executor_cls = m.executor_cls break if matched_executor_cls is None: expected = set() for m in cls._executor_str_matchers: expected.update(m.strings) raise ValueError("Unknown executor string '%s' expected" " one of %s (or mixed case equivalent)" % (desired_executor, list(expected))) else: executor_cls = matched_executor_cls elif desired_executor is not None: matched_executor_cls = None for m in cls._executor_cls_matchers: if m.matches(desired_executor): matched_executor_cls = m.executor_cls break if matched_executor_cls is None: expected = set() for m in cls._executor_cls_matchers: expected.update(m.types) raise TypeError("Unknown executor '%s' (%s) expected an" " instance of %s" % (desired_executor, type(desired_executor), list(expected))) else: executor_cls = matched_executor_cls kwargs['executor'] = desired_executor try: for (k, value_converter) in executor_cls.constructor_options: try: kwargs[k] = value_converter(options[k]) except KeyError: pass except AttributeError: pass return executor_cls(**kwargs)