gh-149388: Make PipeHandle.close idempotent

Clear _handle before calling CloseHandle so a stale handle (closed by
another code path) does not leak OSError into
_ProactorBasePipeTransport._call_connection_lost.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: mxschmitt

Lib/asyncio/windows_utils.py

@@ -111,8 +111,8 @@ def fileno(self):
 
     def close(self, *, CloseHandle=_winapi.CloseHandle):
         if self._handle is not None:
-            CloseHandle(self._handle)
-            self._handle = None
+            handle, self._handle = self._handle, None
+            CloseHandle(handle)
 
     def __del__(self, _warn=warnings.warn):
         if self._handle is not None:

Lib/test/test_asyncio/test_windows_utils.py

@@ -77,6 +77,34 @@ def test_pipe_handle(self):
         else:
             raise RuntimeError('expected ERROR_INVALID_HANDLE')
 
+    def test_pipe_handle_close_after_external_close(self):
+        # gh-149388: PipeHandle.close() must clear ``_handle`` before calling
+        # CloseHandle so that a handle already closed by another code path
+        # does not leak an OSError into the caller (and into
+        # _ProactorBasePipeTransport._call_connection_lost on the proactor
+        # loop, where the error is not caught).
+        h1, h2 = windows_utils.pipe(overlapped=(False, False))
+        try:
+            p = windows_utils.PipeHandle(h1)
+            # Simulate an external close of the underlying handle (e.g.
+            # a finalizer race or a concurrent close on the same object).
+            _winapi.CloseHandle(p.handle)
+            # The OSError from CloseHandle may still surface to the caller,
+            # but ``_handle`` must be cleared first so that __del__ and any
+            # subsequent close() are silent no-ops.
+            try:
+                p.close()
+            except OSError:
+                pass
+            self.assertIsNone(p.handle)
+            # Second close is a no-op.
+            p.close()
+            # __del__ through GC is a no-op too — no unraisable warning.
+            del p
+            support.gc_collect()
+        finally:
+            _winapi.CloseHandle(h2)
+
 
 class PopenTests(unittest.TestCase):
 

Misc/NEWS.d/next/Library/2026-05-07-21-58-17.gh-issue-149388.DDBPeA.rst

@@ -0,0 +1,7 @@
+Make :meth:`!asyncio.windows_utils.PipeHandle.close` idempotent by clearing
+``_handle`` before calling :c:func:`!CloseHandle`. Previously, if the
+underlying Win32 handle had already been closed by another code path, the
+``OSError`` raised by :c:func:`!CloseHandle` would escape through
+:meth:`!_ProactorBasePipeTransport._call_connection_lost` on Windows
+proactor loops and be reported as an unhandled exception to the event
+loop's exception handler.