From 995f6170c78570eca818f7e7dbd8a7661c171a81 Mon Sep 17 00:00:00 2001
From: "Dong Uk, Kang" <nailbrainz@gmail.com>
Date: Wed, 23 Nov 2022 00:06:20 +0900
Subject: [PATCH] gh-88863: Clear ref cycles to resolve leak when
 asyncio.open_connection raises (#95739)

Break reference cycles to resolve memory leak, by
removing local exception and future instances from the frame
---
 Lib/asyncio/base_events.py                    | 31 ++++++++++++-------
 Lib/asyncio/selector_events.py                | 10 +++++-
 Lib/asyncio/windows_events.py                 |  8 ++++-
 ...2-08-06-12-18-07.gh-issue-88863.NnqsuJ.rst |  3 ++
 4 files changed, 38 insertions(+), 14 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2022-08-06-12-18-07.gh-issue-88863.NnqsuJ.rst

diff --git a/Lib/asyncio/base_events.py b/Lib/asyncio/base_events.py
index c8a2f9f2563..91d32e3939d 100644
--- a/Lib/asyncio/base_events.py
+++ b/Lib/asyncio/base_events.py
@@ -986,6 +986,8 @@ async def _connect_sock(self, exceptions, addr_info, local_addr_infos=None):
             if sock is not None:
                 sock.close()
             raise
+        finally:
+            exceptions = my_exceptions = None
 
     async def create_connection(
             self, protocol_factory, host=None, port=None,
@@ -1084,19 +1086,22 @@ async def create_connection(
 
             if sock is None:
                 exceptions = [exc for sub in exceptions for exc in sub]
-                if all_errors:
-                    raise ExceptionGroup("create_connection failed", exceptions)
-                if len(exceptions) == 1:
-                    raise exceptions[0]
-                else:
-                    # If they all have the same str(), raise one.
-                    model = str(exceptions[0])
-                    if all(str(exc) == model for exc in exceptions):
+                try:
+                    if all_errors:
+                        raise ExceptionGroup("create_connection failed", exceptions)
+                    if len(exceptions) == 1:
                         raise exceptions[0]
-                    # Raise a combined exception so the user can see all
-                    # the various error messages.
-                    raise OSError('Multiple exceptions: {}'.format(
-                        ', '.join(str(exc) for exc in exceptions)))
+                    else:
+                        # If they all have the same str(), raise one.
+                        model = str(exceptions[0])
+                        if all(str(exc) == model for exc in exceptions):
+                            raise exceptions[0]
+                        # Raise a combined exception so the user can see all
+                        # the various error messages.
+                        raise OSError('Multiple exceptions: {}'.format(
+                            ', '.join(str(exc) for exc in exceptions)))
+                finally:
+                    exceptions = None
 
         else:
             if sock is None:
@@ -1904,6 +1909,8 @@ def _run_once(self):
 
         event_list = self._selector.select(timeout)
         self._process_events(event_list)
+        # Needed to break cycles when an exception occurs.
+        event_list = None
 
         # Handle 'later' callbacks that are ready.
         end_time = self.time() + self._clock_resolution
diff --git a/Lib/asyncio/selector_events.py b/Lib/asyncio/selector_events.py
index bfa4590154f..3d30006198f 100644
--- a/Lib/asyncio/selector_events.py
+++ b/Lib/asyncio/selector_events.py
@@ -633,7 +633,11 @@ async def sock_connect(self, sock, address):
 
         fut = self.create_future()
         self._sock_connect(fut, sock, address)
-        return await fut
+        try:
+            return await fut
+        finally:
+            # Needed to break cycles when an exception occurs.
+            fut = None
 
     def _sock_connect(self, fut, sock, address):
         fd = sock.fileno()
@@ -655,6 +659,8 @@ def _sock_connect(self, fut, sock, address):
             fut.set_exception(exc)
         else:
             fut.set_result(None)
+        finally:
+            fut = None
 
     def _sock_write_done(self, fd, fut, handle=None):
         if handle is None or not handle.cancelled():
@@ -678,6 +684,8 @@ def _sock_connect_cb(self, fut, sock, address):
             fut.set_exception(exc)
         else:
             fut.set_result(None)
+        finally:
+            fut = None
 
     async def sock_accept(self, sock):
         """Accept a connection.
diff --git a/Lib/asyncio/windows_events.py b/Lib/asyncio/windows_events.py
index acc97daafec..4dad436fb41 100644
--- a/Lib/asyncio/windows_events.py
+++ b/Lib/asyncio/windows_events.py
@@ -439,7 +439,11 @@ def select(self, timeout=None):
             self._poll(timeout)
         tmp = self._results
         self._results = []
-        return tmp
+        try:
+            return tmp
+        finally:
+            # Needed to break cycles when an exception occurs.
+            tmp = None
 
     def _result(self, value):
         fut = self._loop.create_future()
@@ -793,6 +797,8 @@ def _poll(self, timeout=None):
                 else:
                     f.set_result(value)
                     self._results.append(f)
+                finally:
+                    f = None
 
         # Remove unregistered futures
         for ov in self._unregistered:
diff --git a/Misc/NEWS.d/next/Library/2022-08-06-12-18-07.gh-issue-88863.NnqsuJ.rst b/Misc/NEWS.d/next/Library/2022-08-06-12-18-07.gh-issue-88863.NnqsuJ.rst
new file mode 100644
index 00000000000..23f8cb01cf0
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2022-08-06-12-18-07.gh-issue-88863.NnqsuJ.rst
@@ -0,0 +1,3 @@
+To avoid apparent memory leaks when :func:`asyncio.open_connection` raises,
+break reference cycles generated by local exception and future instances
+(which has exception instance as its member var). Patch by Dong Uk, Kang.