#
# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements. See the NOTICE file distributed with
# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You 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
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# 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.
#
"""An executor that schedules and executes applied ptransforms."""
from __future__ import absolute_import
import collections
import logging
import Queue
import sys
import threading
from weakref import WeakValueDictionary
from apache_beam.metrics.execution import MetricsContainer
from apache_beam.metrics.execution import ScopedMetricsContainer
class _ExecutorService(object):
"""Thread pool for executing tasks in parallel."""
class CallableTask(object):
def call(self):
pass
@property
def name(self):
return None
class _ExecutorServiceWorker(threading.Thread):
"""Worker thread for executing a single task at a time."""
# Amount to block waiting for getting an item from the queue in seconds.
TIMEOUT = 5
def __init__(self, queue, index):
super(_ExecutorService._ExecutorServiceWorker, self).__init__()
self.queue = queue
self._index = index
self._default_name = 'ExecutorServiceWorker-' + str(index)
self._update_name()
self.shutdown_requested = False
self.start()
def _update_name(self, task=None):
if task and task.name:
name = task.name
else:
name = self._default_name
self.name = 'Thread: %d, %s (%s)' % (
self._index, name, 'executing' if task else 'idle')
def _get_task_or_none(self):
try:
# Do not block indefinitely, otherwise we may not act for a requested
# shutdown.
return self.queue.get(
timeout=_ExecutorService._ExecutorServiceWorker.TIMEOUT)
except Queue.Empty:
return None
def run(self):
while not self.shutdown_requested:
task = self._get_task_or_none()
if task:
try:
if not self.shutdown_requested:
self._update_name(task)
task.call()
self._update_name()
finally:
self.queue.task_done()
def shutdown(self):
self.shutdown_requested = True
def __init__(self, num_workers):
self.queue = Queue.Queue()
self.workers = [_ExecutorService._ExecutorServiceWorker(
self.queue, i) for i in range(num_workers)]
self.shutdown_requested = False
def submit(self, task):
assert isinstance(task, _ExecutorService.CallableTask)
if not self.shutdown_requested:
self.queue.put(task)
def await_completion(self):
for worker in self.workers:
worker.join()
def shutdown(self):
self.shutdown_requested = True
for worker in self.workers:
worker.shutdown()
# Consume all the remaining items in the queue
while not self.queue.empty():
try:
self.queue.get_nowait()
self.queue.task_done()
except Queue.Empty:
continue
# All existing threads will eventually terminate (after they complete their
# last task).
class _TransformEvaluationState(object):
def __init__(self, executor_service, scheduled):
self.executor_service = executor_service
self.scheduled = scheduled
def schedule(self, work):
self.scheduled.add(work)
self.executor_service.submit(work)
def complete(self, completed_work):
self.scheduled.remove(completed_work)
class _ParallelEvaluationState(_TransformEvaluationState):
"""A TransformEvaluationState with unlimited parallelism.
Any TransformExecutor scheduled will be immediately submitted to the
ExecutorService.
A principal use of this is for evaluators that can generate output bundles
only using the input bundle (e.g. ParDo).
"""
pass
class _SerialEvaluationState(_TransformEvaluationState):
"""A TransformEvaluationState with a single work queue.
Any TransformExecutor scheduled will be placed on the work queue. Only one
item of work will be submitted to the ExecutorService at any time.
A principal use of this is for evaluators that keeps a global state such as
_GroupByKeyOnly.
"""
def __init__(self, executor_service, scheduled):
super(_SerialEvaluationState, self).__init__(executor_service, scheduled)
self.serial_queue = collections.deque()
self.currently_evaluating = None
self._lock = threading.Lock()
def complete(self, completed_work):
self._update_currently_evaluating(None, completed_work)
super(_SerialEvaluationState, self).complete(completed_work)
def schedule(self, new_work):
self._update_currently_evaluating(new_work, None)
def _update_currently_evaluating(self, new_work, completed_work):
with self._lock:
if new_work:
self.serial_queue.append(new_work)
if completed_work:
assert self.currently_evaluating == completed_work
self.currently_evaluating = None
if self.serial_queue and not self.currently_evaluating:
next_work = self.serial_queue.pop()
self.currently_evaluating = next_work
super(_SerialEvaluationState, self).schedule(next_work)
class _TransformExecutorServices(object):
"""Schedules and completes TransformExecutors.
Controls the concurrency as appropriate for the applied transform the executor
exists for.
"""
def __init__(self, executor_service):
self._executor_service = executor_service
self._scheduled = set()
self._parallel = _ParallelEvaluationState(
self._executor_service, self._scheduled)
self._serial_cache = WeakValueDictionary()
def parallel(self):
return self._parallel
def serial(self, step):
cached = self._serial_cache.get(step)
if not cached:
cached = _SerialEvaluationState(self._executor_service, self._scheduled)
self._serial_cache[step] = cached
return cached
@property
def executors(self):
return frozenset(self._scheduled)
class _CompletionCallback(object):
"""The default completion callback.
The default completion callback is used to complete transform evaluations
that are triggered due to the arrival of elements from an upstream transform,
or for a source transform.
"""
def __init__(self, evaluation_context, all_updates, timers=None):
self._evaluation_context = evaluation_context
self._all_updates = all_updates
self._timers = timers
def handle_result(self, input_committed_bundle, transform_result):
output_committed_bundles = self._evaluation_context.handle_result(
input_committed_bundle, self._timers, transform_result)
for output_committed_bundle in output_committed_bundles:
self._all_updates.offer(_ExecutorServiceParallelExecutor._ExecutorUpdate(
output_committed_bundle, None))
return output_committed_bundles
def handle_exception(self, exception):
self._all_updates.offer(
_ExecutorServiceParallelExecutor._ExecutorUpdate(None, exception))
[docs]class Executor(object):
"""For internal use only; no backwards-compatibility guarantees."""
def __init__(self, *args, **kwargs):
self._executor = _ExecutorServiceParallelExecutor(*args, **kwargs)
[docs] def start(self, roots):
self._executor.start(roots)
[docs] def await_completion(self):
self._executor.await_completion()
class _ExecutorServiceParallelExecutor(object):
"""An internal implementation for Executor."""
NUM_WORKERS = 1
def __init__(self, value_to_consumers, transform_evaluator_registry,
evaluation_context):
self.executor_service = _ExecutorService(
_ExecutorServiceParallelExecutor.NUM_WORKERS)
self.transform_executor_services = _TransformExecutorServices(
self.executor_service)
self.value_to_consumers = value_to_consumers
self.transform_evaluator_registry = transform_evaluator_registry
self.evaluation_context = evaluation_context
self.all_updates = _ExecutorServiceParallelExecutor._TypedUpdateQueue(
_ExecutorServiceParallelExecutor._ExecutorUpdate)
self.visible_updates = _ExecutorServiceParallelExecutor._TypedUpdateQueue(
_ExecutorServiceParallelExecutor._VisibleExecutorUpdate)
self.default_completion_callback = _CompletionCallback(
evaluation_context, self.all_updates)
def start(self, roots):
self.root_nodes = frozenset(roots)
self.executor_service.submit(
_ExecutorServiceParallelExecutor._MonitorTask(self))
def await_completion(self):
update = self.visible_updates.take()
try:
if update.exception:
t, v, tb = update.exc_info
raise t, v, tb
finally:
self.executor_service.shutdown()
def schedule_consumers(self, committed_bundle):
if committed_bundle.pcollection in self.value_to_consumers:
consumers = self.value_to_consumers[committed_bundle.pcollection]
for applied_ptransform in consumers:
self.schedule_consumption(applied_ptransform, committed_bundle,
self.default_completion_callback)
def schedule_consumption(self, consumer_applied_transform, committed_bundle,
on_complete):
"""Schedules evaluation of the given bundle with the transform."""
assert all([consumer_applied_transform, on_complete])
assert committed_bundle or consumer_applied_transform in self.root_nodes
if (committed_bundle
and self.transform_evaluator_registry.should_execute_serially(
consumer_applied_transform)):
transform_executor_service = self.transform_executor_services.serial(
consumer_applied_transform)
else:
transform_executor_service = self.transform_executor_services.parallel()
transform_executor = TransformExecutor(
self.transform_evaluator_registry, self.evaluation_context,
committed_bundle, consumer_applied_transform, on_complete,
transform_executor_service)
transform_executor_service.schedule(transform_executor)
class _TypedUpdateQueue(object):
"""Type checking update queue with blocking and non-blocking operations."""
def __init__(self, item_type):
self._item_type = item_type
self._queue = Queue.Queue()
def poll(self):
try:
item = self._queue.get_nowait()
self._queue.task_done()
return item
except Queue.Empty:
return None
def take(self):
item = self._queue.get()
self._queue.task_done()
return item
def offer(self, item):
assert isinstance(item, self._item_type)
self._queue.put_nowait(item)
class _ExecutorUpdate(object):
"""An internal status update on the state of the executor."""
def __init__(self, produced_bundle=None, exception=None):
# Exactly one of them should be not-None
assert bool(produced_bundle) != bool(exception)
self.committed_bundle = produced_bundle
self.exception = exception
self.exc_info = sys.exc_info()
if self.exc_info[1] is not exception:
# Not the right exception.
self.exc_info = (exception, None, None)
class _VisibleExecutorUpdate(object):
"""An update of interest to the user.
Used for awaiting the completion to decide whether to return normally or
raise an exception.
"""
def __init__(self, exc_info=(None, None, None)):
self.finished = exc_info[0] is not None
self.exception = exc_info[1] or exc_info[0]
self.exc_info = exc_info
class _MonitorTask(_ExecutorService.CallableTask):
"""MonitorTask continuously runs to ensure that pipeline makes progress."""
def __init__(self, executor):
self._executor = executor
@property
def name(self):
return 'monitor'
def call(self):
try:
update = self._executor.all_updates.poll()
while update:
if update.committed_bundle:
self._executor.schedule_consumers(update.committed_bundle)
else:
assert update.exception
logging.warning('A task failed with exception.\n %s',
update.exception)
self._executor.visible_updates.offer(
_ExecutorServiceParallelExecutor._VisibleExecutorUpdate(
update.exc_info))
update = self._executor.all_updates.poll()
self._executor.evaluation_context.schedule_pending_unblocked_tasks(
self._executor.executor_service)
self._add_work_if_necessary(self._fire_timers())
except Exception as e: # pylint: disable=broad-except
logging.error('Monitor task died due to exception.\n %s', e)
self._executor.visible_updates.offer(
_ExecutorServiceParallelExecutor._VisibleExecutorUpdate(
sys.exc_info()))
finally:
if not self._should_shutdown():
self._executor.executor_service.submit(self)
def _should_shutdown(self):
"""_should_shutdown checks whether pipeline is completed or not.
It will check for successful completion by checking the watermarks of all
transforms. If they all reached the maximum watermark it means that
pipeline successfully reached to completion.
If the above is not true, it will check that at least one executor is
making progress. Otherwise pipeline will be declared stalled.
If the pipeline reached to a terminal state as explained above
_should_shutdown will request executor to gracefully shutdown.
Returns:
True if pipeline reached a terminal state and monitor task could finish.
Otherwise monitor task should schedule itself again for future
execution.
"""
if self._is_executing():
# There are some bundles still in progress.
return False
else:
if self._executor.evaluation_context.is_done():
self._executor.visible_updates.offer(
_ExecutorServiceParallelExecutor._VisibleExecutorUpdate())
else:
# Nothing is scheduled for execution, but watermarks incomplete.
self._executor.visible_updates.offer(
_ExecutorServiceParallelExecutor._VisibleExecutorUpdate(
(Exception('Monitor task detected a pipeline stall.'),
None,
None)))
self._executor.executor_service.shutdown()
return True
def _fire_timers(self):
"""Schedules triggered consumers if any timers fired.
Returns:
True if timers fired.
"""
fired_timers = self._executor.evaluation_context.extract_fired_timers()
for applied_ptransform in fired_timers:
# Use an empty committed bundle. just to trigger.
empty_bundle = (
self._executor.evaluation_context.create_empty_committed_bundle(
applied_ptransform.inputs[0]))
timer_completion_callback = _CompletionCallback(
self._executor.evaluation_context, self._executor.all_updates,
applied_ptransform)
self._executor.schedule_consumption(
applied_ptransform, empty_bundle, timer_completion_callback)
return bool(fired_timers)
def _is_executing(self):
"""Returns True if there is at least one non-blocked TransformExecutor."""
executors = self._executor.transform_executor_services.executors
if not executors:
# Nothing is executing.
return False
# Ensure that at least one of those executors is not blocked.
for transform_executor in executors:
if not transform_executor.blocked:
return True
return False
def _add_work_if_necessary(self, timers_fired):
"""Adds more work from the roots if pipeline requires more input.
If all active TransformExecutors are in a blocked state, add more work
from root nodes that may have additional work. This ensures that if a
pipeline has elements available from the root nodes it will add those
elements when necessary.
Args:
timers_fired: True if any timers fired prior to this call.
"""
# If any timers have fired, they will add more work; No need to add more.
if timers_fired:
return
if self._is_executing():
# We have at least one executor that can proceed without adding
# additional work.
return
# All current TransformExecutors are blocked; add more work from the
# roots.
for applied_transform in self._executor.root_nodes:
if not self._executor.evaluation_context.is_done(applied_transform):
self._executor.schedule_consumption(
applied_transform, None,
self._executor.default_completion_callback)