Fix UDP socket close hangs on Windows

docs/versionhistory.rst

@@ -17,6 +17,8 @@ This library adheres to `Semantic Versioning 2.0 <http://semver.org/>`_.
   module name. (The default name for a task spawned with ``TaskGroup.start_soon`` or
   ``TaskGroup.start`` typically includes the module name.)
   (`#1234 <https://github.com/agronholm/anyio/pull/1234>`_; PR by @gschaffner)
+- Fixed UDP socket closing hanging on Windows if a datagram send was still in flight
+  (`#1237 <https://github.com/agronholm/anyio/issues/1237>`_; PR by @Guflly)
 - Fixed free-threading compatibility issues arising from the fact that on Python 3.14
   free-threading builds, newly created threads inherit the current context by default,
   causing AnyIO to behave erroneously in relation to ``start_blocking_portal()`` and

src/anyio/_backends/_asyncio.py

@@ -1403,8 +1403,11 @@ async def aclose(self) -> None:
                 pass
 
             self._transport.close()
-            await sleep(0)
-            self._transport.abort()
+            try:
+                await sleep(0)
+            finally:
+                self._transport.abort()
+                await AsyncIOBackend.cancel_shielded_checkpoint()
 
 
 class _RawSocketMixin:
@@ -1687,6 +1690,11 @@ async def aclose(self) -> None:
         self._closed = True
         if not self._transport.is_closing():
             self._transport.close()
+            try:
+                await sleep(0)
+            finally:
+                self._transport.abort()
+                await AsyncIOBackend.cancel_shielded_checkpoint()
 
         await self._protocol.closed_event.wait()
 
@@ -1737,6 +1745,11 @@ async def aclose(self) -> None:
         self._closed = True
         if not self._transport.is_closing():
             self._transport.close()
+            try:
+                await sleep(0)
+            finally:
+                self._transport.abort()
+                await AsyncIOBackend.cancel_shielded_checkpoint()
 
         await self._protocol.closed_event.wait()
 

tests/test_sockets.py

@@ -34,6 +34,7 @@
 from pytest import FixtureRequest
 from pytest_mock.plugin import MockerFixture
 
+import anyio
 from anyio import (
     BrokenResourceError,
     BusyResourceError,
@@ -518,6 +519,14 @@ async def test_send_after_close(self, server_addr: tuple[str, int]) -> None:
         with pytest.raises(ClosedResourceError):
             await stream.send(b"foo")
 
+    @pytest.mark.parametrize("anyio_backend", asyncio_params)
+    async def test_aclose_forcefully(self, server_addr: tuple[str, int]) -> None:
+        stream = await connect_tcp(*server_addr)
+        sock = stream.extra(SocketAttribute.raw_socket)
+        await stream.send(b"x")
+        await anyio.aclose_forcefully(stream)
+        assert sock.fileno() == -1
+
     async def test_receive_after_peer_closed(
         self, family: AnyIPAddressFamily, request: FixtureRequest
     ) -> None:
@@ -1743,6 +1752,17 @@ async def test_aclose_waits_for_fd_release(
             udp = await UDPSocket.from_socket(sock)
             await udp.aclose()
 
+    @pytest.mark.skipif(sys.platform != "win32", reason="Windows only")
+    @pytest.mark.parametrize("anyio_backend", asyncio_params)
+    async def test_aclose_during_send(self) -> None:
+        udp = await create_udp_socket(local_host="127.0.0.1")
+        sock = udp.extra(SocketAttribute.raw_socket)
+        await udp.sendto(b"x", "127.0.0.1", 9999)
+        with fail_after(1):
+            await anyio.aclose_forcefully(udp)
+
+        assert sock.fileno() == -1
+
     async def test_extra_attributes(self, family: AnyIPAddressFamily) -> None:
         async with await create_udp_socket(
             family=family, local_host="localhost"
@@ -1914,6 +1934,14 @@ async def test_aclose_waits_for_fd_release(
         finally:
             peer.close()
 
+    @pytest.mark.skipif(sys.platform != "win32", reason="Windows only")
+    @pytest.mark.parametrize("anyio_backend", asyncio_params)
+    async def test_aclose_during_send(self) -> None:
+        udp = await create_connected_udp_socket("127.0.0.1", 9999)
+        await udp.send(b"x")
+        with fail_after(1):
+            await udp.aclose()
+
     async def test_extra_attributes(self, family: AnyIPAddressFamily) -> None:
         async with await create_connected_udp_socket(
             "localhost", 5000, family=family