# taskflow.retry

# Source code for taskflow.retry

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

    #    Copyright (C) 2013 Rackspace Hosting Inc. All Rights Reserved.
    #    Copyright (C) 2013 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
    #
    #         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.

    import abc

    import enum

    from taskflow import atom
    from taskflow import exceptions as exc
    from taskflow.utils import misc

    @enum.unique
    class Decision(misc.StrEnum):
        """Decision results/strategy enumeration."""

        REVERT = "REVERT"
        """Reverts only the surrounding/associated subflow.

        This strategy first consults the parent atom before reverting the
        associated subflow to determine if the parent retry object provides a
        different reconciliation strategy.  This allows for safe nesting of
        flows with different retry strategies.

        If the parent flow has no retry strategy, the default behavior is
        to just revert the atoms in the associated subflow.  This is
        generally not the desired behavior, but is left as the default in
        order to keep backwards-compatibility.  The ``defer_reverts``
        engine option will let you change this behavior.  If that is set
        to True, a REVERT will always defer to the parent, meaning that
        if the parent has no retry strategy, it will be reverted as well.
        """

        REVERT_ALL = "REVERT_ALL"
        """Reverts the entire flow, regardless of parent strategy.

        This strategy will revert every atom that has executed thus
        far, regardless of whether the parent flow has a separate
        retry strategy associated with it.
        """

        #: Retries the surrounding/associated subflow again.
        RETRY = "RETRY"

    # Retain these aliases for a number of releases...
    REVERT = Decision.REVERT
    REVERT_ALL = Decision.REVERT_ALL
    RETRY = Decision.RETRY

    # Constants passed into revert/execute kwargs.
    #
    # Contains information about the past decisions and outcomes that have
    # occurred (if available).
    EXECUTE_REVERT_HISTORY = 'history'
    #
    # The cause of the flow failure/s
    REVERT_FLOW_FAILURES = 'flow_failures'

    class History(object):
        """Helper that simplifies interactions with retry historical contents."""

        def __init__(self, contents, failure=None):
            self._contents = contents
            self._failure = failure

        @property
        def failure(self):
            """Returns the retries own failure or none if not existent."""
            return self._failure

        def outcomes_iter(self, index=None):
            """Iterates over the contained failure outcomes.

            If the index is not provided, then all outcomes are iterated over.

            NOTE(harlowja): if the retry itself failed, this will **not** include
            those types of failures. Use the :py:attr:`.failure` attribute to
            access that instead (if it exists, aka, non-none).
            """
            if index is None:
                contents = self._contents
            else:
                contents = [
                    self._contents[index],
                ]
            for (provided, outcomes) in contents:
                for (owner, outcome) in outcomes.items():
                    yield (owner, outcome)

        def __len__(self):
            return len(self._contents)

        def provided_iter(self):
            """Iterates over all the values the retry has attempted (in order)."""
            for (provided, outcomes) in self._contents:
                yield provided

        def __getitem__(self, index):
            return self._contents[index]

        def caused_by(self, exception_cls, index=None, include_retry=False):
            """Checks if the exception class provided caused the failures.

            If the index is not provided, then all outcomes are iterated over.

            NOTE(harlowja): only if ``include_retry`` is provided as true (defaults
                            to false) will the potential retries own failure be
                            checked against as well.
            """
            for (name, failure) in self.outcomes_iter(index=index):
                if failure.check(exception_cls):
                    return True
            if include_retry and self._failure is not None:
                if self._failure.check(exception_cls):
                    return True
            return False

        def __iter__(self):
            """Iterates over the raw contents of this history object."""
            return iter(self._contents)

    class Retry(atom.Atom, metaclass=abc.ABCMeta):
        """A class that can decide how to resolve execution failures.

        This abstract base class is used to inherit from and provide different
        strategies that will be activated upon execution failures. Since a retry
        object is an atom it may also provide :meth:`~taskflow.retry.Retry.execute`
        and :meth:`~taskflow.retry.Retry.revert` methods to alter the inputs of
        connected atoms (depending on the desired strategy to be used this can be
        quite useful).

        NOTE(harlowja): the :meth:`~taskflow.retry.Retry.execute` and
        :meth:`~taskflow.retry.Retry.revert` and
        :meth:`~taskflow.retry.Retry.on_failure` will automatically be given
        a ``history`` parameter, which contains information about the past
        decisions and outcomes that have occurred (if available).
        """

        def __init__(self, name=None, provides=None, requires=None,
                     auto_extract=True, rebind=None):
            super(Retry, self).__init__(name=name, provides=provides,
                                        requires=requires, rebind=rebind,
                                        auto_extract=auto_extract,
                                        ignore_list=[EXECUTE_REVERT_HISTORY])

        @property
        def name(self):
            return self._name

        @name.setter
        def name(self, name):
            self._name = name

        @abc.abstractmethod
        def execute(self, history, *args, **kwargs):
            """Executes the given retry.

            This execution activates a given retry which will typically produce
            data required to start or restart a connected component using
            previously provided values and a ``history`` of prior failures from
            previous runs. The historical data can be analyzed to alter the
            resolution strategy that this retry controller will use.

            For example, a retry can provide the same values multiple times (after
            each run), the latest value or some other variation. Old values will be
            saved to the history of the retry atom automatically, that is a list of
            tuples (result, failures) are persisted where failures is a dictionary
            of failures indexed by task names and the result is the execution
            result returned by this retry during that failure resolution
            attempt.

            :param args: positional arguments that retry requires to execute.
            :param kwargs: any keyword arguments that retry requires to execute.
            """

        def revert(self, history, *args, **kwargs):
            """Reverts this retry.

            On revert call all results that had been provided by previous tries
            and all errors caused during reversion are provided. This method
            will be called *only* if a subflow must be reverted without the
            retry (that is to say that the controller has ran out of resolution
            options and has either given up resolution or has failed to handle
            a execution failure).

            :param args: positional arguments that the retry required to execute.
            :param kwargs: any keyword arguments that the retry required to
                           execute.
            """

        @abc.abstractmethod
        def on_failure(self, history, *args, **kwargs):
            """Makes a decision about the future.

            This method will typically use information about prior failures (if
            this historical failure information is not available or was not
            persisted the provided history will be empty).

            Returns a retry constant (one of):

            * ``RETRY``: when the controlling flow must be reverted and restarted
              again (for example with new parameters).
            * ``REVERT``: when this controlling flow must be completely reverted
              and the parent flow (if any) should make a decision about further
              flow execution.
            * ``REVERT_ALL``: when this controlling flow and the parent
              flow (if any) must be reverted and marked as a ``FAILURE``.
            """

    class AlwaysRevert(Retry):
        """Retry that always reverts subflow."""

        def on_failure(self, *args, **kwargs):
            return REVERT

        def execute(self, *args, **kwargs):
            pass

    class AlwaysRevertAll(Retry):
        """Retry that always reverts a whole flow."""

        def on_failure(self, **kwargs):
            return REVERT_ALL

        def execute(self, **kwargs):
            pass

    class Times(Retry):
        """Retries subflow given number of times. Returns attempt number.

        :param attempts: number of attempts to retry the associated subflow
                         before giving up
        :type attempts: int
        :param revert_all: when provided this will cause the full flow to revert
                           when the number of attempts that have been tried
                           has been reached (when false, it will only locally
                           revert the associated subflow)
        :type revert_all: bool

        Further arguments are interpreted as defined in the
        :py:class:`~taskflow.atom.Atom` constructor.
        """

        def __init__(self, attempts=1, name=None, provides=None, requires=None,
                     auto_extract=True, rebind=None, revert_all=False):
            super(Times, self).__init__(name, provides, requires,
                                        auto_extract, rebind)
            self._attempts = attempts

            if revert_all:
                self._revert_action = REVERT_ALL
            else:
                self._revert_action = REVERT

        def on_failure(self, history, *args, **kwargs):
            if len(history) < self._attempts:
                return RETRY
            return self._revert_action

        def execute(self, history, *args, **kwargs):
            return len(history) + 1

    class ForEachBase(Retry):
        """Base class for retries that iterate over a given collection."""

        def __init__(self, name=None, provides=None, requires=None,
                     auto_extract=True, rebind=None, revert_all=False):
            super(ForEachBase, self).__init__(name, provides, requires,
                                              auto_extract, rebind)

            if revert_all:
                self._revert_action = REVERT_ALL
            else:
                self._revert_action = REVERT

        def _get_next_value(self, values, history):
            # Fetches the next resolution result to try, removes overlapping
            # entries with what has already been tried and then returns the first
            # resolution strategy remaining.
            remaining = misc.sequence_minus(values, history.provided_iter())
            if not remaining:
                raise exc.NotFound("No elements left in collection of iterable "
                                   "retry controller %s" % self.name)
            return remaining[0]

        def _on_failure(self, values, history):
            try:
                self._get_next_value(values, history)
            except exc.NotFound:
                return self._revert_action
            else:
                return RETRY

    class ForEach(ForEachBase):
        """Applies a statically provided collection of strategies.

        Accepts a collection of decision strategies on construction and returns the
        next element of the collection on each try.

        :param values: values collection to iterate over and provide to
                       atoms other in the flow as a result of this functions
                       :py:meth:`~taskflow.atom.Atom.execute` method, which
                       other dependent atoms can consume (for example, to alter
                       their own behavior)
        :type values: list
        :param revert_all: when provided this will cause the full flow to revert
                           when the number of attempts that have been tried
                           has been reached (when false, it will only locally
                           revert the associated subflow)
        :type revert_all: bool

        Further arguments are interpreted as defined in the
        :py:class:`~taskflow.atom.Atom` constructor.
        """

        def __init__(self, values, name=None, provides=None, requires=None,
                     auto_extract=True, rebind=None, revert_all=False):
            super(ForEach, self).__init__(name, provides, requires,
                                          auto_extract, rebind, revert_all)
            self._values = values

        def on_failure(self, history, *args, **kwargs):
            return self._on_failure(self._values, history)

        def execute(self, history, *args, **kwargs):
            # NOTE(harlowja): This allows any connected components to know the
            # current resolution strategy being attempted.
            return self._get_next_value(self._values, history)

    class ParameterizedForEach(ForEachBase):
        """Applies a dynamically provided collection of strategies.

        Accepts a collection of decision strategies from a predecessor (or from
        storage) as a parameter and returns the next element of that collection on
        each try.

        :param revert_all: when provided this will cause the full flow to revert
                           when the number of attempts that have been tried
                           has been reached (when false, it will only locally
                           revert the associated subflow)
        :type revert_all: bool

        Further arguments are interpreted as defined in the
        :py:class:`~taskflow.atom.Atom` constructor.
        """

        def __init__(self, name=None, provides=None, requires=None,
                     auto_extract=True, rebind=None, revert_all=False):
            super(ParameterizedForEach, self).__init__(name, provides, requires,
                                                       auto_extract, rebind,
                                                       revert_all)

        def on_failure(self, values, history, *args, **kwargs):
            return self._on_failure(values, history)

        def execute(self, values, history, *args, **kwargs):
            return self._get_next_value(values, history)

this page last updated: 2025-02-27 12:56:39

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