Add support for wait_readable() and wait_writable() on ProactorEventLoop

docs/versionhistory.rst

@@ -12,7 +12,9 @@ This library adheres to `Semantic Versioning 2.0 <http://semver.org/>`_.
 - Added the ``wait_readable()`` and ``wait_writable()`` functions which will accept
   an object with a ``.fileno()`` method or an integer handle, and deprecated
   their now obsolete versions (``wait_socket_readable()`` and
-  ``wait_socket_writable()`` (PR by @davidbrochart)
+  ``wait_socket_writable()``) (PR by @davidbrochart)
+- Added support for ``wait_readable()`` and ``wait_writable()`` on ``ProactorEventLoop``
+  (used on asyncio + Windows by default)
 - Fixed the return type annotations of ``readinto()`` and ``readinto1()`` methods in the
   ``anyio.AsyncFile`` class
   (`#825 <https://github.com/agronholm/anyio/issues/825>`_)

src/anyio/_backends/_asyncio.py

@@ -103,7 +103,9 @@
 from ..streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
 
 if TYPE_CHECKING:
-    from _typeshed import HasFileno
+    from _typeshed import FileDescriptorLike
+else:
+    FileDescriptorLike = object
 
 if sys.version_info >= (3, 10):
     from typing import ParamSpec
@@ -2734,7 +2736,7 @@ async def getnameinfo(
         return await get_running_loop().getnameinfo(sockaddr, flags)
 
     @classmethod
-    async def wait_readable(cls, obj: HasFileno | int) -> None:
+    async def wait_readable(cls, obj: FileDescriptorLike) -> None:
         await cls.checkpoint()
         try:
             read_events = _read_events.get()
@@ -2746,25 +2748,30 @@ async def wait_readable(cls, obj: HasFileno | int) -> None:
             obj = obj.fileno()
 
         if read_events.get(obj):
-            raise BusyResourceError("reading from") from None
+            raise BusyResourceError("reading from")
 
         loop = get_running_loop()
-        event = read_events[obj] = asyncio.Event()
-        loop.add_reader(obj, event.set)
+        event = asyncio.Event()
+        try:
+            loop.add_reader(obj, event.set)
+        except NotImplementedError:
+            from anyio._core._asyncio_selector_thread import get_selector
+
+            selector = get_selector()
+            selector.add_reader(obj, event.set)
+            remove_reader = selector.remove_reader
+        else:
+            remove_reader = loop.remove_reader
+
+        read_events[obj] = event
         try:
             await event.wait()
         finally:
-            if read_events.pop(obj, None) is not None:
-                loop.remove_reader(obj)
-                readable = True
-            else:
-                readable = False
-
-        if not readable:
-            raise ClosedResourceError
+            remove_reader(obj)
+            del read_events[obj]
 
     @classmethod
-    async def wait_writable(cls, obj: HasFileno | int) -> None:
+    async def wait_writable(cls, obj: FileDescriptorLike) -> None:
         await cls.checkpoint()
         try:
             write_events = _write_events.get()
@@ -2776,22 +2783,27 @@ async def wait_writable(cls, obj: HasFileno | int) -> None:
             obj = obj.fileno()
 
         if write_events.get(obj):
-            raise BusyResourceError("writing to") from None
+            raise BusyResourceError("writing to")
 
         loop = get_running_loop()
-        event = write_events[obj] = asyncio.Event()
-        loop.add_writer(obj, event.set)
+        event = asyncio.Event()
+        try:
+            loop.add_writer(obj, event.set)
+        except NotImplementedError:
+            from anyio._core._asyncio_selector_thread import get_selector
+
+            selector = get_selector()
+            selector.add_writer(obj, event.set)
+            remove_writer = selector.remove_writer
+        else:
+            remove_writer = loop.remove_writer
+
+        write_events[obj] = event
         try:
             await event.wait()
         finally:
-            if write_events.pop(obj, None) is not None:
-                loop.remove_writer(obj)
-                writable = True
-            else:
-                writable = False
-
-        if not writable:
-            raise ClosedResourceError
+            del write_events[obj]
+            remove_writer(obj)
 
     @classmethod
     def current_default_thread_limiter(cls) -> CapacityLimiter:

src/anyio/_core/_asyncio_selector_thread.py

@@ -0,0 +1,150 @@
+from __future__ import annotations
+
+import asyncio
+import socket
+import threading
+from collections.abc import Callable
+from selectors import EVENT_READ, EVENT_WRITE, DefaultSelector
+from typing import TYPE_CHECKING, Any
+
+if TYPE_CHECKING:
+    from _typeshed import FileDescriptorLike
+
+_selector_lock = threading.Lock()
+_selector: Selector | None = None
+
+
+class Selector:
+    def __init__(self) -> None:
+        self._thread = threading.Thread(target=self.run, name="AnyIO socket selector")
+        self._selector = DefaultSelector()
+        self._send, self._receive = socket.socketpair()
+        self._send.setblocking(False)
+        self._receive.setblocking(False)
+        self._selector.register(self._receive, EVENT_READ)
+        self._closed = False
+
+    def start(self) -> None:
+        self._thread.start()
+        threading._register_atexit(self._stop)  # type: ignore[attr-defined]
+
+    def _stop(self) -> None:
+        global _selector
+        self._closed = True
+        self._notify_self()
+        self._send.close()
+        self._thread.join()
+        self._selector.unregister(self._receive)
+        self._receive.close()
+        self._selector.close()
+        _selector = None
+        assert (
+            not self._selector.get_map()
+        ), "selector still has registered file descriptors after shutdown"
+
+    def _notify_self(self) -> None:
+        try:
+            self._send.send(b"\x00")
+        except BlockingIOError:
+            pass
+
+    def add_reader(self, fd: FileDescriptorLike, callback: Callable[[], Any]) -> None:
+        loop = asyncio.get_running_loop()
+        try:
+            key = self._selector.get_key(fd)
+        except KeyError:
+            self._selector.register(fd, EVENT_READ, {EVENT_READ: (loop, callback)})
+        else:
+            if EVENT_READ in key.data:
+                raise ValueError(
+                    "this file descriptor is already registered for reading"
+                )
+
+            key.data[EVENT_READ] = loop, callback
+            self._selector.modify(fd, key.events | EVENT_READ, key.data)
+
+        self._notify_self()
+
+    def add_writer(self, fd: FileDescriptorLike, callback: Callable[[], Any]) -> None:
+        loop = asyncio.get_running_loop()
+        try:
+            key = self._selector.get_key(fd)
+        except KeyError:
+            self._selector.register(fd, EVENT_WRITE, {EVENT_WRITE: (loop, callback)})
+        else:
+            if EVENT_WRITE in key.data:
+                raise ValueError(
+                    "this file descriptor is already registered for writing"
+                )
+
+            key.data[EVENT_WRITE] = loop, callback
+            self._selector.modify(fd, key.events | EVENT_WRITE, key.data)
+
+        self._notify_self()
+
+    def remove_reader(self, fd: FileDescriptorLike) -> bool:
+        try:
+            key = self._selector.get_key(fd)
+        except KeyError:
+            return False
+
+        if new_events := key.events ^ EVENT_READ:
+            del key.data[EVENT_READ]
+            self._selector.modify(fd, new_events, key.data)
+        else:
+            self._selector.unregister(fd)
+
+        return True
+
+    def remove_writer(self, fd: FileDescriptorLike) -> bool:
+        try:
+            key = self._selector.get_key(fd)
+        except KeyError:
+            return False
+
+        if new_events := key.events ^ EVENT_WRITE:
+            del key.data[EVENT_WRITE]
+            self._selector.modify(fd, new_events, key.data)
+        else:
+            self._selector.unregister(fd)
+
+        return True
+
+    def run(self) -> None:
+        while not self._closed:
+            for key, events in self._selector.select():
+                if key.fileobj is self._receive:
+                    try:
+                        while self._receive.recv(4096):
+                            pass
+                    except BlockingIOError:
+                        pass
+
+                    continue
+
+                if events & EVENT_READ:
+                    loop, callback = key.data[EVENT_READ]
+                    self.remove_reader(key.fd)
+                    try:
+                        loop.call_soon_threadsafe(callback)
+                    except RuntimeError:
+                        pass  # the loop was already closed
+
+                if events & EVENT_WRITE:
+                    loop, callback = key.data[EVENT_WRITE]
+                    self.remove_writer(key.fd)
+                    try:
+                        loop.call_soon_threadsafe(callback)
+                    except RuntimeError:
+                        pass  # the loop was already closed
+
+
+def get_selector() -> Selector:
+    global _selector
+
+    with _selector_lock:
+        if _selector is None:
+            _selector = Selector()
+            _selector.start()
+
+        return _selector

src/anyio/_core/_sockets.py

@@ -32,9 +32,9 @@
 from ._tasks import create_task_group, move_on_after
 
 if TYPE_CHECKING:
-    from _typeshed import HasFileno
+    from _typeshed import FileDescriptorLike
 else:
-    HasFileno = object
+    FileDescriptorLike = object
 
 if sys.version_info < (3, 11):
     from exceptiongroup import ExceptionGroup
@@ -609,9 +609,6 @@ def wait_socket_readable(sock: socket.socket) -> Awaitable[None]:
 
     Wait until the given socket has data to be read.
 
-    This does **NOT** work on Windows when using the asyncio backend with a proactor
-    event loop (default on py3.8+).
-
     .. warning:: Only use this on raw sockets that have not been wrapped by any higher
         level constructs like socket streams!
 
@@ -649,7 +646,7 @@ def wait_socket_writable(sock: socket.socket) -> Awaitable[None]:
     return get_async_backend().wait_writable(sock.fileno())
 
 
-def wait_readable(obj: HasFileno | int) -> Awaitable[None]:
+def wait_readable(obj: FileDescriptorLike) -> Awaitable[None]:
     """
     Wait until the given object has data to be read.
 
@@ -663,10 +660,12 @@ def wait_readable(obj: HasFileno | int) -> Awaitable[None]:
     descriptors aren't supported, and neither are handles that refer to anything besides
     a ``SOCKET``.
 
-    This does **NOT** work on Windows when using the asyncio backend with a proactor
-    event loop (default on py3.8+).
+    On backends where this functionality is not natively provided (asyncio
+    ``ProactorEventLoop`` on Windows) Additionally, on asyncio, this functionality is
+    provided using a separate selector thread which is set to shut down when the
+    interpreter shuts down.
 
-    .. warning:: Only use this on raw sockets that have not been wrapped by any higher
+    .. warning:: Don't use this on raw sockets that have been wrapped by any higher
         level constructs like socket streams!
 
     :param obj: an object with a ``.fileno()`` method or an integer handle
@@ -679,25 +678,22 @@ def wait_readable(obj: HasFileno | int) -> Awaitable[None]:
     return get_async_backend().wait_readable(obj)
 
 
-def wait_writable(obj: HasFileno | int) -> Awaitable[None]:
+def wait_writable(obj: FileDescriptorLike) -> Awaitable[None]:
     """
     Wait until the given object can be written to.
 
-    This does **NOT** work on Windows when using the asyncio backend with a proactor
-    event loop (default on py3.8+).
-
-    .. seealso:: See the documentation of :func:`wait_readable` for the definition of
-       ``obj``.
-
-    .. warning:: Only use this on raw sockets that have not been wrapped by any higher
-        level constructs like socket streams!
-
     :param obj: an object with a ``.fileno()`` method or an integer handle
     :raises ~anyio.ClosedResourceError: if the object was closed while waiting for the
         object to become writable
     :raises ~anyio.BusyResourceError: if another task is already waiting for the object
         to become writable
 
+    .. seealso:: See the documentation of :func:`wait_readable` for the definition of
+       ``obj`` and notes on backend compatibility.
+
+    .. warning:: Don't use this on raw sockets that have been wrapped by any higher
+        level constructs like socket streams!
+
     """
     return get_async_backend().wait_writable(obj)
 

tests/test_sockets.py

@@ -65,7 +65,7 @@
     from exceptiongroup import ExceptionGroup
 
 if TYPE_CHECKING:
-    from _typeshed import HasFileno
+    from _typeshed import FileDescriptorLike
 
 AnyIPAddressFamily = Literal[
     AddressFamily.AF_UNSPEC, AddressFamily.AF_INET, AddressFamily.AF_INET6
@@ -1858,16 +1858,7 @@ async def test_connect_tcp_getaddrinfo_context() -> None:
 
 @pytest.mark.parametrize("socket_type", ["socket", "fd"])
 @pytest.mark.parametrize("event", ["readable", "writable"])
-async def test_wait_socket(
-    anyio_backend_name: str, event: str, socket_type: str
-) -> None:
-    if anyio_backend_name == "asyncio" and platform.system() == "Windows":
-        import asyncio
-
-        policy = asyncio.get_event_loop_policy()
-        if policy.__class__.__name__ == "WindowsProactorEventLoopPolicy":
-            pytest.skip("Does not work on asyncio/Windows/ProactorEventLoop")
-
+async def test_wait_socket(event: str, socket_type: str) -> None:
     wait = wait_readable if event == "readable" else wait_writable
 
     with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as server_sock:
@@ -1880,20 +1871,15 @@ async def test_wait_socket(
 
         conn, addr = server_sock.accept()
         with conn:
-            sock_or_fd: HasFileno | int = conn.fileno() if socket_type == "fd" else conn
-            with fail_after(10):
+            sock_or_fd: FileDescriptorLike = (
+                conn.fileno() if socket_type == "fd" else conn
+            )
+            with fail_after(3):
                 await wait(sock_or_fd)
                 assert conn.recv(1024) == b"Hello, world"
 
 
 async def test_deprecated_wait_socket(anyio_backend_name: str) -> None:
-    if anyio_backend_name == "asyncio" and platform.system() == "Windows":
-        import asyncio
-
-        policy = asyncio.get_event_loop_policy()
-        if policy.__class__.__name__ == "WindowsProactorEventLoopPolicy":
-            pytest.skip("Does not work on asyncio/Windows/ProactorEventLoop")
-
     with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
         with pytest.warns(
             DeprecationWarning,