feat(processors): add a SplitGatherProcessor (#17)

Add `sghi.etl.commons.processors.SplitGatherProcessor`, a `Processor`
that splits aggregated raw data into its constituent data parts and then
processes each data part concurrently.

src/sghi/etl/commons/__init__.py

@@ -3,6 +3,7 @@
 from .processors import (
     NOOPProcessor,
     ProcessorPipe,
+    SplitGatherProcessor,
     pipe_processors,
     processor,
 )
@@ -17,6 +18,7 @@
     "NullSink",
     "ProcessorPipe",
     "SimpleWorkflowDefinition",
+    "SplitGatherProcessor",
     "fail_fast",
     "fail_fast_factory",
     "ignored_failed",

src/sghi/etl/commons/processors.py

@@ -3,7 +3,8 @@
 from __future__ import annotations
 
 import logging
-from collections.abc import Callable, Sequence
+from collections.abc import Callable, Iterable, Sequence
+from concurrent.futures import Executor, Future, ThreadPoolExecutor
 from contextlib import ExitStack
 from functools import update_wrapper
 from logging import Logger
@@ -14,8 +15,16 @@
 from sghi.disposable import not_disposed
 from sghi.etl.core import Processor
 from sghi.retry import Retry, noop_retry
-from sghi.task import Task, pipe, task
-from sghi.utils import ensure_callable, ensure_not_none_nor_empty, type_fqn
+from sghi.task import ConcurrentExecutor, Task, pipe, task
+from sghi.utils import (
+    ensure_callable,
+    ensure_instance_of,
+    ensure_not_none_nor_empty,
+    ensure_predicate,
+    type_fqn,
+)
+
+from .utils import fail_fast
 
 # =============================================================================
 # TYPES
@@ -28,8 +37,12 @@
 _RDT = TypeVar("_RDT")
 """Type variable representing the raw data type."""
 
+_T = TypeVar("_T")
+
 _ProcessorCallable = Callable[[_RDT], _PDT]
 
+_ResultGatherer = Callable[[Iterable[Future[_T]]], Iterable[_T]]
+
 
 # =============================================================================
 # CONSTANTS
@@ -328,6 +341,249 @@ def do_apply(raw_data: _RDT) -> _PDT:
 pipe_processors = ProcessorPipe
 
 
+@final
+class SplitGatherProcessor(
+    Processor[Sequence[_RDT], Sequence[_PDT]], Generic[_RDT, _PDT]
+):
+    """A :class:`Processor` that splits raw data and applies multiple
+    processors to the split data.
+
+    This ``Processor`` implementation takes aggregated raw data, splits it into
+    its constituent data parts, and then processes each data part concurrently.
+    This is achieved by mapping each data part to an embedded processor before
+    executing all the embedded processors concurrently. As such, the supplied
+    raw data's size must equal the number of embedded processors contained by a
+    processor of this type. A result gatherer function can be provided to
+    specify how to handle processing errors and/or which results from the
+    embedded processors to pick. A :class:`retry policy<Retry>` to handle
+    transient processing errors of the embedded processors can also be
+    provided. A suitable :class:`Executor` can be specified at instantiation to
+    control the concurrent application of the embedded processors.
+
+    Instances of this class are **NOT SAFE** to retry and **SHOULD NEVER** be
+    retried. However, they do support retrying their embedded processors. This
+    is disabled by default but can be enabled by providing a suitable value to
+    the ``retry_policy_factory`` constructor parameter when creating new
+    instances. When enabled, each embedded processor will be retried
+    individually per the specified retry policy in case it fails.
+
+    Disposing instances of this class also disposes of their embedded
+    processors.
+
+    .. admonition:: Regarding retry safety
+        :class: tip
+
+        Instances of this ``Processor`` are **NOT SAFE** to retry.
+    """  # noqa: D205
+
+    __slots__ = (
+        "_processors",
+        "_retry_policy_factory",
+        "_executor_factory",
+        "_result_gatherer",
+        "_is_disposed",
+        "_logger",
+        "_exit_stack",
+        "_prepped_processors",
+        "_executor",
+    )
+
+    def __init__(
+        self,
+        processors: Sequence[Processor[_RDT, _PDT]],
+        retry_policy_factory: Callable[[], Retry] = noop_retry,
+        executor_factory: Callable[[], Executor] = ThreadPoolExecutor,
+        result_gatherer: _ResultGatherer[_PDT] = fail_fast,
+    ) -> None:
+        """Create a new ``SplitGatherProcessor`` of the given properties.
+
+        :param processors: A ``Sequence`` of processors to apply to each raw
+            data part. These processors are also referred to as the embedded
+            processors. The given ``Sequence`` *MUST NOT* be empty.
+        :param retry_policy_factory: A callable that supplies retry policy
+            instance(s) to apply to each embedded processor. This *MUST* be a
+            valid callable object. Defaults to a factory that returns retry
+            policies that do nothing.
+        :param executor_factory: A callable that suppliers suitable
+            ``Executor`` instance(s) to use for the concurrent processing. This
+            *MUST* be a valid callable object. Defaults to a factory that
+            returns ``ThreadPoolExecutor`` instances.
+        :param result_gatherer: A function that specifies how to handle
+            processing errors and/or which results from the embedded processors
+            to pick. This *MUST* be a valid callable object. Defaults to a
+            gatherer that fails if applying any of the embedded processors
+            failed, or returns all the processed data otherwise.
+
+        :raise TypeError: If ``processors`` is NOT a ``Sequence``.
+        :raise ValueError: If ``processors`` is empty or if
+            ``retry_policy_factory``, ``executor_factory`` and
+            ``result_gatherer`` are NOT callable objects.
+        """
+        super().__init__()
+        ensure_not_none_nor_empty(
+            value=ensure_instance_of(
+                value=processors,
+                message=(
+                    "'processors' MUST be a collections.abc.Sequence object."
+                ),
+                klass=Sequence,
+            ),
+            message="'processors' MUST NOT be empty.",
+        )
+        self._retry_policy_factory: Callable[[], Retry] = ensure_callable(
+            value=retry_policy_factory,
+            message="'retry_policy_factory' MUST be a callable.",
+        )
+        self._executor_factory: Callable[[], Executor] = ensure_callable(
+            value=executor_factory,
+            message="'executor_factory' MUST be a callable.",
+        )
+        self._result_gatherer: _ResultGatherer[_PDT] = ensure_callable(
+            value=result_gatherer,
+            message="'result_gatherer' MUST be a callable.",
+        )
+        self._processors: Sequence[Processor[_RDT, _PDT]] = tuple(processors)
+        self._is_disposed: bool = False
+        self._logger: Logger = logging.getLogger(type_fqn(self.__class__))
+        self._exit_stack: ExitStack = ExitStack()
+
+        # Prepare embedded processors for execution by ensuring that they are
+        # all disposed of properly once this object is disposed.
+        self._prepped_processors: Sequence[Task[Any, Any]] = tuple(
+            self._processor_to_task(self._exit_stack.push(_processor), _i)
+            for _i, _processor in enumerate(self._processors)
+        )
+        self._executor: ConcurrentExecutor[Sequence[_RDT], _PDT]
+        self._executor = ConcurrentExecutor(
+            *self._prepped_processors, executor=self._executor_factory()
+        )
+
+    @not_disposed
+    @override
+    def __enter__(self) -> Self:
+        """Return ``self`` upon entering the runtime context.
+
+        .. admonition:: Don't use after dispose
+            :class: error
+
+            Invoking this method on an instance that is disposed(i.e. the
+            :attr:`is_disposed` property on the instance is ``True``) will
+            result in a :exc:`ResourceDisposedError` being raised.
+
+        :return: This instance.
+
+        :raise ResourceDisposedError: If this processor has already been
+            disposed.
+        """
+        return super(Processor, self).__enter__()
+
+    @property
+    @override
+    def is_disposed(self) -> bool:
+        return self._is_disposed
+
+    @not_disposed
+    @override
+    def apply(self, raw_data: Sequence[_RDT]) -> Sequence[_PDT]:
+        """Split the supplied raw data, process it and return the results.
+
+        This method decomposes the provided aggregated raw data into its
+        constituent data parts and maps each data part to an embedded
+        processor; before executing all the embedded processors concurrently.
+        It then applies the result-gatherer function assigned to this instance
+        (at creation) to the :class:`Future` objects resulting from the
+        concurrent execution. Each of these ``Future`` objects wraps the result
+        of processing each data part using an embedded processor contained in
+        this ``SplitGatherProcessor``, and they preserve the same order.
+
+        The contents of the resulting aggregate, and their ordering, are
+        determined by the provided result-gatherer function. That is, the
+        contents of the returned ``Sequence``, will be the same as those
+        returned by this object's result-gatherer function and in the same
+        order.
+
+        .. admonition:: Don't use after dispose
+            :class: error
+
+            Invoking this method on an instance that is disposed(i.e. the
+            :attr:`is_disposed` property on the instance is ``True``) will
+            result in a :exc:`ResourceDisposedError` being raised.
+
+        :param raw_data: The aggregated raw data to process. This *MUST* be a
+            ``Sequence`` of raw data values whose size *MUST EQUAL* the number
+            of embedded processors contained by this ``SplitGatherProcessor``.
+
+        :return: The aggregated results of applying the embedded processors to
+            the provided raw data.
+
+        :raise ResourceDisposedError: If this processor has already been
+            disposed.
+        :raise TypeError: If ``raw_data`` *IS NOT* a ``Sequence``.
+        :raise ValueError: If the size of ``raw_data`` *DOES NOT EQUAL* the
+            number of embedded processors in this ``SplitGatherProcessor``.
+        """
+        ensure_instance_of(
+            value=raw_data,
+            klass=Sequence,
+            message="'raw_data' MUST be a collections.abc.Sequence object.",
+        )
+        ensure_predicate(
+            test=len(raw_data) == len(self._processors),
+            message=(
+                f"Expected 'raw_data' to be of size {len(self._processors)} "
+                f"but got size {len(raw_data)} instead."
+            ),
+            exc_factory=ValueError,
+        )
+        self._logger.info(
+            "Splitting aggregated raw data and applying available processors "
+            "to each data part."
+        )
+
+        with self._executor as executor:
+            futures = executor.execute(raw_data)
+
+        return tuple(self._result_gatherer(futures))
+
+    @override
+    def dispose(self) -> None:
+        """Release any underlying resources contained by this processor.
+
+        All embedded processors are also disposed. After this method returns
+        successfully, the :attr:`is_disposed` property should return ``True``.
+
+        .. note::
+            Unless otherwise specified, trying to use methods of a
+            ``Disposable`` instance decorated with the
+            :func:`~sghi.disposable.not_disposed` decorator after this method
+            returns should generally be considered a programming error and
+            should result in a :exc:`~sghi.disposable.ResourceDisposedError`
+            being raised.
+
+            This method should be idempotent allowing it to be called more
+            than once; only the first call, however, should have an effect.
+
+        :return: None.
+        """
+        self._is_disposed = True
+        self._exit_stack.close()
+        self._executor.dispose()
+        self._logger.info("Disposal complete.")
+
+    def _processor_to_task(
+        self,
+        p: Processor[_RDT, _PDT],
+        i: int,
+    ) -> Task[Sequence[_RDT], _PDT]:
+        @task
+        def do_apply(raw_data: Sequence[_RDT]) -> _PDT:
+            with p as _p:
+                apply = self._retry_policy_factory().retry(_p.apply)
+                return apply(raw_data[i])
+
+        return do_apply
+
+
 @final
 class _ProcessorOfCallable(Processor[_RDT, _PDT], Generic[_RDT, _PDT]):
     __slots__ = ("_delegate_to", "_is_disposed", "_logger")
@@ -405,6 +661,7 @@ def dispose(self) -> None:
 __all__ = [
     "NOOPProcessor",
     "ProcessorPipe",
+    "SplitGatherProcessor",
     "pipe_processors",
     "processor",
 ]