gh-88863: Clear ref cycles to resolve leak when asyncio.open_connecti…

…on raises (#95739)

Break reference cycles to resolve memory leak, by
removing local exception and future instances from the frame

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

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.

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:

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.