airflow/utils/mixins.py

#
# 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.

from __future__ import annotations

import multiprocessing
import typing

from airflow.configuration import conf
from airflow.utils.context import Context

if typing.TYPE_CHECKING:
    import multiprocessing.context

    from airflow.models.operator import Operator


class MultiprocessingStartMethodMixin:
    """Convenience class to add support for different types of multiprocessing."""

    def _get_multiprocessing_start_method(self) -> str:
        """
        Determine method of creating new processes by checking if the
        mp_start_method is set in configs, else, it uses the OS default.
        """
        if conf.has_option("core", "mp_start_method"):
            return conf.get_mandatory_value("core", "mp_start_method")

        method = multiprocessing.get_start_method()
        if not method:
            raise ValueError("Failed to determine start method")
        return method

    def _get_multiprocessing_context(self) -> multiprocessing.context.DefaultContext:
        mp_start_method = self._get_multiprocessing_start_method()
        return multiprocessing.get_context(mp_start_method)  # type: ignore


class ResolveMixin:
    """A runtime-resolved value."""

    def iter_references(self) -> typing.Iterable[tuple[Operator, str]]:
        """Find underlying XCom references this contains.

        This is used by the DAG parser to recursively find task dependencies.

        :meta private:
        """
        raise NotImplementedError

    def resolve(self, context: Context) -> typing.Any:
        """Resolve this value for runtime.

        :meta private:
        """
        raise NotImplementedError