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parsl.py
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parsl.py
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import logging
from functools import partial
from queue import Queue
from threading import Thread
from concurrent.futures import wait, Future
from time import sleep, perf_counter
from typing import Optional, List, Callable, Tuple, Dict, Union, Set
import parsl
from parsl import python_app
from parsl.app.python import PythonApp
from parsl.dataflow.futures import AppFuture
from colmena.method_server.base import BaseMethodServer
from colmena.redis.queue import MethodServerQueues
from colmena.models import Result
logger = logging.getLogger(__name__)
def run_and_record_timing(func: Callable, result: Result) -> Result:
"""Run a function and also return the runtime
Args:
func: Function to invoke
result: Result object describing task request
Returns:
Result object with the serialized result
"""
# Mark that compute has started on the worker
result.mark_compute_started()
# Unpack the inputs
result.time_deserialize_inputs = result.deserialize()
# Execute the function
start_time = perf_counter()
output = func(*result.args, **result.kwargs)
end_time = perf_counter()
result.set_result(output, end_time - start_time)
# Re-pack the results
result.time_serialize_results = result.serialize()
return result
@python_app(executors=['local_threads'])
def output_result(queues: MethodServerQueues, topic: str, inputs: Result, result_obj):
"""Submit the function result to the Redis queue
Args:
queues: Queues used to communicate with Redis
topic: Topic to assign in output queue
inputs: [Not used by this function]
result_obj: Result object containing the inputs, to be sent back with outputs
"""
assert inputs is not None # Inputs are not used currently, are passed with the task for the error handler
return queues.send_result(result_obj, topic=topic)
class _ErrorHandler(Thread):
"""Keeps track of the Parsl futures and reports back errors"""
def __init__(self, future_queue: Queue, timeout: float = 5):
"""
Args:
future_queue (Queue): A queue on which to receive
timeout (float): How long to wait before checking for new futures
"""
super().__init__(daemon=True, name='error_handler')
self.future_queue = future_queue
self.timeout = timeout
def run(self) -> None:
# Initialize the list of futures
logger.info('Starting the error-handler thread')
futures: Set[Future] = set()
# Continually look for new jobs
while True:
# Pull from the queue until empty
# This operation assumes we have only one thread reading from the queue
# Otherwise, the queue could become empty between checking status and then pulling
while not self.future_queue.empty():
futures.add(self.future_queue.get())
# If no futures, wait for the timeout
if len(futures) == 0:
sleep(self.timeout)
else:
done, not_done = wait(futures, timeout=self.timeout)
# If there are entries that are complete, check if they have errors
for task in done:
# Check if an exception was raised
exc = task.exception()
if exc is None:
logger.debug(f'Task completed: {task}')
continue
logger.debug(f'Task {task} with an exception: {exc}')
# Pull out the result objects
queues: MethodServerQueues = task.task_def['args'][0]
topic: str = task.task_def['args'][1]
result_obj: Result = task.task_def['args'][2]
result_obj.success = False
queues.send_result(result_obj, topic=topic)
# Loop through the incomplete tasks
futures = not_done
class ParslMethodServer(BaseMethodServer):
"""Method server based on Parsl
Create a Parsl method server by first configuring Parsl following
the recommendations in `the Parsl documentation
<https://parsl.readthedocs.io/en/stable/userguide/configuring.html>`_.
Then instantiate a method server with a list of functions and
configurations defining on which Parsl executors each function can run.
The executor(s) for each function can be defined with a combination
of per method specifications
.. code-block:: python
ParslMethodServer([(f, {'executors': ['a']})])
and also using a default executor
.. code-block:: python
ParslMethodServer([f], default_executors=['a'])
Further configuration options for each method can be defined
in the list of methods.
**Technical Details**
The method server stores each of the supplied methods as Parsl "PythonApp" classes.
Tasks are launched using these PythonApps after being received on the queue.
The Future provided when requesting the method invocation is then passed
to second PythonApp that pushes the result of the function to the output
queue after it completes.
That second, "output_result," function runs on threads of the same
process as this method server.
"""
def __init__(self, methods: List[Union[Callable, Tuple[Callable, Dict]]],
queues: MethodServerQueues, timeout: Optional[int] = None,
default_executors: Union[str, List[str]] = 'all'):
"""
Args:
methods (list): List of methods to be served.
Each element in the list is either a function or a tuple where the first element
is a function and the second is a dictionary of the arguments being used to create
the Parsl ParslApp see `Parsl documentation
<https://parsl.readthedocs.io/en/stable/stubs/parsl.app.app.python_app.html#parsl.app.app.python_app>`_.
queues (MethodServerQueues): Queues for the method server
timeout (int): Timeout, if desired
default_executors: Executor or list of executors to use by default.
"""
super().__init__(queues, timeout)
# Assemble the list of methods
self.methods_ = {}
for method in methods:
# Get the options or use the defaults
if isinstance(method, tuple):
if len(method) != 2:
raise ValueError('Method description should a tuple of length 2')
function, options = method
else:
function = method
options = {'executors': default_executors}
if default_executors == 'all':
logger.warning(f'Method {function.__name__} may run on the method server\'s local threads.'
' Consider specifying default_executors')
# Make the Parsl app
name = function.__name__
# Wrap the function in the timer class
wrapped_function = partial(run_and_record_timing, function)
app = PythonApp(wrapped_function, **options)
# Store it
self.methods_[name] = app
logger.info(f'Defined {len(self.methods_)} methods: {", ".join(self.methods_.keys())}')
# If only one method, store a default method
self.default_method_ = list(self.methods_.keys())[0] if len(self.methods_) else None
if self.default_method_ is not None:
logger.info(f'There is only one method, so we are using {self.default_method_} as a default')
# Create a thread to check if tasks completed successfully
self.task_queue = Queue()
self.error_checker = _ErrorHandler(self.task_queue)
self.error_checker.start()
def process_queue(self):
"""Evaluate a single task from the queue"""
# Get a result from the queue
# TODO (wardlt): Objects are deserialized here, serialized again and then sent to the worker.
# We could implement a method to still read the task but ignore serialization
topic, result = self.queues.get_task(self.timeout)
logger.info(f'Received request for {result.method} with topic {topic}')
# Determine which method to run
if self.default_method_ and result.method is None:
method = self.default_method_
else:
method = result.method
# Submit the application
future = self.submit_application(method, result)
# TODO (wardlt): Implement "resubmit if task returns a new future."
# Requires waiting on two streams: input_queue and the queues
# Pass the future of that operation to the output queue
result_future = output_result(self.queues, topic, result.copy(), future)
logger.debug('Pushed task to Parsl')
# Pass the task to the "error handler"
self.task_queue.put(result_future)
def submit_application(self, method_name: str, result: Result) -> AppFuture:
"""Submit an application to run via Parsl
Args:
method_name (str): Name of the method to invoke
result: Task description
"""
return self.methods_[method_name](result)
def _cleanup(self):
"""Close out any resources needed by the method server"""
# Wait until all tasks have finished
dfk = parsl.dfk()
dfk.wait_for_current_tasks()
logger.info(f"All tasks have completed for {self.__class__.__name__} on {self.ident}")