Source code for distributed.recreate_tasks

import logging

from dask.utils import stringify

from .client import futures_of, wait
from .utils import sync
from .utils_comm import pack_data
from .worker import _deserialize

logger = logging.getLogger(__name__)


class ReplayTaskScheduler:
    """A plugin for the scheduler to recreate tasks locally

    This adds the following routes to the scheduler

    *  get_runspec
    *  get_error_cause
    """

    def __init__(self, scheduler):
        self.scheduler = scheduler
        self.scheduler.handlers["get_runspec"] = self.get_runspec
        self.scheduler.handlers["get_error_cause"] = self.get_error_cause
        self.scheduler.extensions["replay-tasks"] = self

    def _process_key(self, key):
        if isinstance(key, list):
            key = tuple(key)  # ensure not a list from msgpack
        key = stringify(key)
        return key

    def get_error_cause(self, *args, keys=(), **kwargs):
        for key in keys:
            key = self._process_key(key)
            ts = self.scheduler.tasks.get(key)
            if ts is not None and ts.exception_blame is not None:
                return ts.exception_blame.key

    def get_runspec(self, *args, key=None, **kwargs):
        key = self._process_key(key)
        ts = self.scheduler.tasks.get(key)
        return {"task": ts.run_spec, "deps": [dts.key for dts in ts.dependencies]}


[docs]class ReplayTaskClient: """ A plugin for the client allowing replay of remote tasks locally Adds the following methods to the given client: - ``recreate_error_locally``: main user method for replaying failed tasks - ``recreate_task_locally``: main user method for replaying any task """ def __init__(self, client): self.client = client self.client.extensions["replay-tasks"] = self # monkey patch self.client._get_raw_components_from_future = ( self._get_raw_components_from_future ) self.client._prepare_raw_components = self._prepare_raw_components self.client._get_components_from_future = self._get_components_from_future self.client._get_errored_future = self._get_errored_future self.client.recreate_task_locally = self.recreate_task_locally self.client.recreate_error_locally = self.recreate_error_locally @property def scheduler(self): return self.client.scheduler async def _get_raw_components_from_future(self, future): """ For a given future return the func, args and kwargs and future deps that would be executed remotely. """ if isinstance(future, str): key = future else: await wait(future) key = future.key spec = await self.scheduler.get_runspec(key=key) deps, task = spec["deps"], spec["task"] if isinstance(task, dict): function, args, kwargs = _deserialize(**task) return (function, args, kwargs, deps) else: function, args, kwargs = _deserialize(task=task) return (function, args, kwargs, deps) async def _prepare_raw_components(self, raw_components): """ Take raw components and resolve future dependencies. """ function, args, kwargs, deps = raw_components futures = self.client._graph_to_futures({}, deps) data = await self.client._gather(futures) args = pack_data(args, data) kwargs = pack_data(kwargs, data) return (function, args, kwargs) async def _get_components_from_future(self, future): """ For a given future return the func, args and kwargs that would be executed remotely. Any args/kwargs that are themselves futures will be resolved to the return value of those futures. """ raw_components = await self._get_raw_components_from_future(future) return await self._prepare_raw_components(raw_components)
[docs] def recreate_task_locally(self, future): """ For any calculation, whether it succeeded or failed, perform the task locally for debugging. This operation should be performed after a future (result of ``gather``, ``compute``, etc) comes back with a status other than "pending". Cases where you might want to debug a successfully completed future could include a calculation that returns an unexpected results. A common debugging process might include running the task locally in debug mode, with `pdb.runcall`. Examples -------- >>> import pdb # doctest: +SKIP >>> future = c.submit(div, 1, 1) # doctest: +SKIP >>> future.status # doctest: +SKIP 'finished' >>> pdb.runcall(c.recreate_task_locally, future) # doctest: +SKIP Parameters ---------- future : future The same thing as was given to ``gather``. Returns ------- Any; will return the result of the task future. """ func, args, kwargs = sync( self.client.loop, self._get_components_from_future, future ) return func(*args, **kwargs)
async def _get_errored_future(self, future): """ For a given future collection, return the first future that raised an error. """ await wait(future) futures = [f.key for f in futures_of(future) if f.status == "error"] if not futures: raise ValueError("No errored futures passed") cause_key = await self.scheduler.get_error_cause(keys=futures) return cause_key
[docs] def recreate_error_locally(self, future): """ For a failed calculation, perform the blamed task locally for debugging. This operation should be performed after a future (result of ``gather``, ``compute``, etc) comes back with a status of "error", if the stack- trace is not informative enough to diagnose the problem. The specific task (part of the graph pointing to the future) responsible for the error will be fetched from the scheduler, together with the values of its inputs. The function will then be executed, so that ``pdb`` can be used for debugging. Examples -------- >>> future = c.submit(div, 1, 0) # doctest: +SKIP >>> future.status # doctest: +SKIP 'error' >>> c.recreate_error_locally(future) # doctest: +SKIP ZeroDivisionError: division by zero If you're in IPython you might take this opportunity to use pdb >>> %pdb # doctest: +SKIP Automatic pdb calling has been turned ON >>> c.recreate_error_locally(future) # doctest: +SKIP ZeroDivisionError: division by zero 1 def div(x, y): ----> 2 return x / y ipdb> Parameters ---------- future : future or collection that failed The same thing as was given to ``gather``, but came back with an exception/stack-trace. Can also be a (persisted) dask collection containing any errored futures. Returns ------- Nothing; the function runs and should raise an exception, allowing the debugger to run. """ errored_future_key = sync(self.client.loop, self._get_errored_future, future) return self.recreate_task_locally(errored_future_key)