gh-155003: Don't try to close mmap in SharedMemory.__del__

Lib/multiprocessing/shared_memory.py

@@ -186,7 +186,7 @@ def __init__(self, name=None, create=False, size=0, *, track=True):
 
     def __del__(self):
         try:
-            self.close()
+            self._closefd()
         except OSError:
             pass
 
@@ -222,6 +222,11 @@ def size(self):
         "Size in bytes."
         return self._size
 
+    def _closefd(self):
+        if _USE_POSIX and self._fd >= 0:
+            os.close(self._fd)
+            self._fd = -1
+
     def close(self):
         """Closes access to the shared memory from this instance but does
         not destroy the shared memory block."""
@@ -231,9 +236,7 @@ def close(self):
         if self._mmap is not None:
             self._mmap.close()
             self._mmap = None
-        if _USE_POSIX and self._fd >= 0:
-            os.close(self._fd)
-            self._fd = -1
+        self._closefd()
 
     def unlink(self):
         """Requests that the underlying shared memory block be destroyed.

Misc/NEWS.d/next/Library/2026-08-02-08-43-20.gh-issue-155003.VVy9Z_.rst

@@ -0,0 +1,2 @@
+Fix an error in the finalizer of :class:`multiprocessing.shared_memory.SharedMemory`
+which could leak a file descriptor.