Re-organize directory structure (#4971)

See discussion in #2491

Co-authored-by: Ivan Levkivskyi <ilevkivskyi@dropbox.com>

stdlib/multiprocessing/pool.pyi

@@ -0,0 +1,90 @@
+import sys
+from typing import Any, Callable, ContextManager, Generic, Iterable, Iterator, List, Mapping, Optional, TypeVar
+
+if sys.version_info >= (3, 9):
+    from types import GenericAlias
+
+_PT = TypeVar("_PT", bound=Pool)
+_S = TypeVar("_S")
+_T = TypeVar("_T")
+
+class ApplyResult(Generic[_T]):
+    def get(self, timeout: Optional[float] = ...) -> _T: ...
+    def wait(self, timeout: Optional[float] = ...) -> None: ...
+    def ready(self) -> bool: ...
+    def successful(self) -> bool: ...
+    if sys.version_info >= (3, 9):
+        def __class_getitem__(cls, item: Any) -> GenericAlias: ...
+
+# alias created during issue #17805
+AsyncResult = ApplyResult
+
+class MapResult(ApplyResult[List[_T]]): ...
+
+class IMapIterator(Iterator[_T]):
+    def __iter__(self: _S) -> _S: ...
+    def next(self, timeout: Optional[float] = ...) -> _T: ...
+    def __next__(self, timeout: Optional[float] = ...) -> _T: ...
+
+class IMapUnorderedIterator(IMapIterator[_T]): ...
+
+class Pool(ContextManager[Pool]):
+    def __init__(
+        self,
+        processes: Optional[int] = ...,
+        initializer: Optional[Callable[..., None]] = ...,
+        initargs: Iterable[Any] = ...,
+        maxtasksperchild: Optional[int] = ...,
+        context: Optional[Any] = ...,
+    ) -> None: ...
+    def apply(self, func: Callable[..., _T], args: Iterable[Any] = ..., kwds: Mapping[str, Any] = ...) -> _T: ...
+    def apply_async(
+        self,
+        func: Callable[..., _T],
+        args: Iterable[Any] = ...,
+        kwds: Mapping[str, Any] = ...,
+        callback: Optional[Callable[[_T], None]] = ...,
+        error_callback: Optional[Callable[[BaseException], None]] = ...,
+    ) -> AsyncResult[_T]: ...
+    def map(self, func: Callable[[_S], _T], iterable: Iterable[_S], chunksize: Optional[int] = ...) -> List[_T]: ...
+    def map_async(
+        self,
+        func: Callable[[_S], _T],
+        iterable: Iterable[_S],
+        chunksize: Optional[int] = ...,
+        callback: Optional[Callable[[_T], None]] = ...,
+        error_callback: Optional[Callable[[BaseException], None]] = ...,
+    ) -> MapResult[_T]: ...
+    def imap(self, func: Callable[[_S], _T], iterable: Iterable[_S], chunksize: Optional[int] = ...) -> IMapIterator[_T]: ...
+    def imap_unordered(
+        self, func: Callable[[_S], _T], iterable: Iterable[_S], chunksize: Optional[int] = ...
+    ) -> IMapIterator[_T]: ...
+    def starmap(self, func: Callable[..., _T], iterable: Iterable[Iterable[Any]], chunksize: Optional[int] = ...) -> List[_T]: ...
+    def starmap_async(
+        self,
+        func: Callable[..., _T],
+        iterable: Iterable[Iterable[Any]],
+        chunksize: Optional[int] = ...,
+        callback: Optional[Callable[[_T], None]] = ...,
+        error_callback: Optional[Callable[[BaseException], None]] = ...,
+    ) -> AsyncResult[List[_T]]: ...
+    def close(self) -> None: ...
+    def terminate(self) -> None: ...
+    def join(self) -> None: ...
+    def __enter__(self: _PT) -> _PT: ...
+
+class ThreadPool(Pool, ContextManager[ThreadPool]):
+    def __init__(
+        self, processes: Optional[int] = ..., initializer: Optional[Callable[..., Any]] = ..., initargs: Iterable[Any] = ...
+    ) -> None: ...
+
+# undocumented
+if sys.version_info >= (3, 8):
+    INIT: str
+    RUN: str
+    CLOSE: str
+    TERMINATE: str
+else:
+    RUN: int
+    CLOSE: int
+    TERMINATE: int