Endless recursion in repr of asyncio.Future if a callback uses the Future itself as argument #93837

usiems · 2022-06-15T09:28:07Z

Bug report

I encountered an endless recursion when doing a repr of a asyncio.Future where a callback, which references the Future itself through functools.partial, is added. This crashes when doing this in a Debug version of Python, but somehow recovers on the Release version.

Try this to reproduce:

import asyncio
import functools

def test():
  fut = asyncio.Future()
  def done_cb(arg):
    pass
  fut.add_done_callback(functools.partial(done_cb, fut))

  print(repr(fut))

test()

The output in the Release version is

<Future pending cb=[test..done_cb(<Future pendi...ion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>

where you can see at least part of the recursion.

An incomplete fix for the recursion problem has already been done for bpo-42183, but this didn't cover the callbacks.

Your environment

CPython versions tested on: Python 3.9.12, 3.9.11 (self-compiled)
Operating system and architecture: Windows, Intel

Propose patch

I have a patch that fixes the problem for me by including all of the Future's state in the recursion guard:

diff --git i/Lib/asyncio/base_futures.py w/Lib/asyncio/base_futures.py
index 2c01ac9..ee60e93 100644
--- i/Lib/asyncio/base_futures.py
+++ w/Lib/asyncio/base_futures.py
@@ -55,26 +55,24 @@ _repr_running = set()
 def _future_repr_info(future):
     # (Future) -> str
     """helper function for Future.__repr__"""
-    info = [future._state.lower()]
-    if future._state == _FINISHED:
-        if future._exception is not None:
-            info.append(f'exception={future._exception!r}')
-        else:
-            key = id(future), get_ident()
-            if key in _repr_running:
-                result = '...'
-            else:
-                _repr_running.add(key)
-                try:
-                    # use reprlib to limit the length of the output, especially
-                    # for very long strings
-                    result = reprlib.repr(future._result)
-                finally:
-                    _repr_running.discard(key)
-            info.append(f'result={result}')
-    if future._callbacks:
-        info.append(_format_callbacks(future._callbacks))
-    if future._source_traceback:
-        frame = future._source_traceback[-1]
-        info.append(f'created at {frame[0]}:{frame[1]}')
-    return info
+
+    key = id(future), get_ident()
+    if key in _repr_running:
+        return ['... [recursion]']
+    else:
+        _repr_running.add(key)
+        try:
+            info = [future._state.lower()]
+            if future._state == _FINISHED:
+                # use reprlib to limit the length of the output, especially
+                # for very long strings
+                result = reprlib.repr(future._result)
+                info.append(f'result={result}')
+            if future._callbacks:
+                info.append(_format_callbacks(future._callbacks))
+            if future._source_traceback:
+                frame = future._source_traceback[-1]
+                info.append(f'created at {frame[0]}:{frame[1]}')
+            return info
+        finally:
+            _repr_running.discard(key)

The text was updated successfully, but these errors were encountered:

kumaraditya303 · 2022-06-15T11:09:05Z

Can you specify what should be the intended behavior? From the title it seems that you are getting a recursion error which isn't the case.
I tried it on main branch debug build and there was no error. Also Python 3.9 is security fix only so you should test Python 3.10+.

usiems · 2022-06-15T12:37:45Z

This is just a thing we stumbled over in MeVisLab 3.5, where we currently use Python 3.9.11. I believe the recursion error is caught internally by reprlib, but it crashes in the Debug mode of MeVisLab, possibly because the stack segment isn't big enough then.

Anyway, I believe this should be caught early. I had a look at the code and it doesn't seem this is caught other than by running into the recursion limit, which seems to be risky.

You can make the recursion visible by setting self.maxother = 10000 in reprlib.py, then you get

<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future pending cb=[test.<locals>.done_cb(<Future instance at 0x1f405c14cc0>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>)() at C:\Users\usiems\Documents\MeVisLab\future_repr_recursion_bug.py:6]>

The <Future instance at 0x1f405c14cc0> in the middle is where Repr.repr_instance catches the recursion error. The string is normally shortened afterwards.

I also checked with Python 3.10.5, the behavior hasn't changed.

usiems · 2022-06-15T12:44:32Z

I was also able to provoke a crash by adding
sys.setrecursionlimit(3000)
to the test

kumaraditya303 · 2022-07-12T09:26:12Z

I am unable to reproduce the crash with this:

import sys
sys.setrecursionlimit(3000)
import asyncio
import functools

def test():
  fut = asyncio.Future()
  def done_cb(arg):
    pass
  fut.add_done_callback(functools.partial(done_cb, fut))

  print(repr(fut))

test()

It would be better if you can provide a complete script to reproduce it and test it on main branch.

usiems · 2022-07-13T16:30:16Z

Hi!
This is a modified full script:

import asyncio
import functools
import sys

sys.setrecursionlimit(3000)

def test():
  fut = asyncio.Future()
  def done_cb(arg):
    pass
  fut.add_done_callback(functools.partial(done_cb, fut))

  print(repr(fut))

try:
  test()
except:
  print("Done")

I noticed that if I run this on Windows from a GIT bash, it isn't apparent that the script crashed, one is just missing some output after the DeprecationWarning (obviously you should at least see "Done"). If you run this from a CMD shell, you get a crash dialog.
(Tested with Python 3.10.5 on Windows, installer downloaded from www.python.org).

kumaraditya303 · 2022-07-13T17:36:29Z

Reproduced on Python 3.10.5 (tags/v3.10.5:f377153, Jun 6 2022, 16:14:13) [MSC v.1929 64 bit (AMD64)] on win32
It is a stack overflow:

D:\python\main\main.py:8: DeprecationWarning: There is no current event loop
  fut = asyncio.Future()
Windows fatal exception: stack overflow

Current thread 0x00001280 (most recent call first):
  File "C:\Program Files\Python310\lib\reprlib.py", line 52 in repr
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 38 in <genexpr>
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 38 in _format_args_and_kwargs
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 56 in _format_callback
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 47 in _format_callback
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 23 in _format_callback_source
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 32 in format_cb
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 35 in _format_callbacks
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 76 in _future_repr_info
  File "C:\Program Files\Python310\lib\reprlib.py", line 139 in repr_instance
  File "C:\Program Files\Python310\lib\reprlib.py", line 62 in repr1
  File "C:\Program Files\Python310\lib\reprlib.py", line 52 in repr
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 38 in <genexpr>
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 38 in _format_args_and_kwargs
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 56 in _format_callback
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 47 in _format_callback
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 23 in _format_callback_source
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 32 in format_cb
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 35 in _format_callbacks
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 76 in _future_repr_info
  File "C:\Program Files\Python310\lib\reprlib.py", line 139 in repr_instance
  File "C:\Program Files\Python310\lib\reprlib.py", line 62 in repr1
  File "C:\Program Files\Python310\lib\reprlib.py", line 52 in repr
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 38 in <genexpr>
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 38 in _format_args_and_kwargs
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 56 in _format_callback
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 47 in _format_callback
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 23 in _format_callback_source
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 32 in format_cb
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 35 in _format_callbacks
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 76 in _future_repr_info
  File "C:\Program Files\Python310\lib\reprlib.py", line 139 in repr_instance
  File "C:\Program Files\Python310\lib\reprlib.py", line 62 in repr1
  File "C:\Program Files\Python310\lib\reprlib.py", line 52 in repr
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 38 in <genexpr>
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 38 in _format_args_and_kwargs
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 56 in _format_callback
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 47 in _format_callback
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 23 in _format_callback_source
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 32 in format_cb
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 35 in _format_callbacks
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 76 in _future_repr_info
  File "C:\Program Files\Python310\lib\reprlib.py", line 139 in repr_instance
  File "C:\Program Files\Python310\lib\reprlib.py", line 62 in repr1
  File "C:\Program Files\Python310\lib\reprlib.py", line 52 in repr
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 38 in <genexpr>
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 38 in _format_args_and_kwargs
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 56 in _format_callback
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 47 in _format_callback
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 23 in _format_callback_source
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 32 in format_cb
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 35 in _format_callbacks
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 76 in _future_repr_info
  File "C:\Program Files\Python310\lib\reprlib.py", line 139 in repr_instance
  File "C:\Program Files\Python310\lib\reprlib.py", line 62 in repr1
  File "C:\Program Files\Python310\lib\reprlib.py", line 52 in repr
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 38 in <genexpr>
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 38 in _format_args_and_kwargs
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 56 in _format_callback
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 47 in _format_callback
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 23 in _format_callback_source
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 32 in format_cb
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 35 in _format_callbacks
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 76 in _future_repr_info
  File "C:\Program Files\Python310\lib\reprlib.py", line 139 in repr_instance
  File "C:\Program Files\Python310\lib\reprlib.py", line 62 in repr1
  File "C:\Program Files\Python310\lib\reprlib.py", line 52 in repr
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 38 in <genexpr>
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 38 in _format_args_and_kwargs
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 56 in _format_callback
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 47 in _format_callback
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 23 in _format_callback_source
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 32 in format_cb
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 35 in _format_callbacks
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 76 in _future_repr_info
  File "C:\Program Files\Python310\lib\reprlib.py", line 139 in repr_instance
  File "C:\Program Files\Python310\lib\reprlib.py", line 62 in repr1
  File "C:\Program Files\Python310\lib\reprlib.py", line 52 in repr
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 38 in <genexpr>
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 38 in _format_args_and_kwargs
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 56 in _format_callback
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 47 in _format_callback
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 23 in _format_callback_source
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 32 in format_cb
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 35 in _format_callbacks
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 76 in _future_repr_info
  File "C:\Program Files\Python310\lib\reprlib.py", line 139 in repr_instance
  File "C:\Program Files\Python310\lib\reprlib.py", line 62 in repr1
  File "C:\Program Files\Python310\lib\reprlib.py", line 52 in repr
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 38 in <genexpr>
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 38 in _format_args_and_kwargs
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 56 in _format_callback
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 47 in _format_callback
  File "C:\Program Files\Python310\lib\asyncio\format_helpers.py", line 23 in _format_callback_source
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 32 in format_cb
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 35 in _format_callbacks
  File "C:\Program Files\Python310\lib\asyncio\base_futures.py", line 76 in _future_repr_info
  File "C:\Program Files\Python310\lib\reprlib.py", line 139 in repr_instance
  File "C:\Program Files\Python310\lib\reprlib.py", line 62 in repr1
  File "C:\Program Files\Python310\lib\reprlib.py", line 52 in repr
  ...

However it is documented ¹ that manually setting sys.setrecursionlimit to a high value can cause stack overflow depending upon the platform.

https://docs.python.org/3.8/library/sys.html#sys.setrecursionlimit ↩

usiems · 2022-08-05T12:24:26Z

I just want to repeat my point, that an (potential) endless recursion in this method should be avoided.

The recursion isn't visible because the RecursionError is caught in the code and I proposed to increase the recursion limit to prove that there indeed is a problem, even if it normally isn't visible.

At minimum this is a potential performance issue (because a lot of code is executed pointlessly to produce a string which is dropped for the most part)

Under certain circumstances this line in `aiorun` can trigger the following Python bug python/cpython#93837 The program will crash with a stack overflow error, probably because the call to log the task about the be cancelled will call repr on a task that references itself somehow.

asvetlov · 2024-11-12T11:41:43Z

I think it is fixed by #91195 for Python 3.11+

freakboy3742 · 2024-11-13T03:29:48Z

@asvetlov Was the added OS-ios tag intentional? I can't see an obvious connection to iOS here...

asvetlov · 2024-11-13T04:17:12Z

@freakboy3742 sorry, OS-ios tag was added by an accident.

usiems added the type-bug An unexpected behavior, bug, or error label Jun 15, 2022

hugovk added the stdlib Python modules in the Lib dir label Jun 15, 2022

kumaraditya303 added the pending The issue will be closed if no feedback is provided label Jun 15, 2022

ezio-melotti added this to asyncio Jun 20, 2022

ezio-melotti moved this to Todo in asyncio Jul 17, 2022

iritkatriel removed the pending The issue will be closed if no feedback is provided label Sep 19, 2022

StefanD986 mentioned this issue May 7, 2024

Workaround for aiorun triggering stackoverflow in Python cjrh/aiorun#88

Merged

willingc added the topic-asyncio label Jun 21, 2024

asvetlov closed this as completed Nov 12, 2024

github-project-automation bot moved this from Todo to Done in asyncio Nov 12, 2024

asvetlov added the OS-ios label Nov 12, 2024

asvetlov removed the OS-ios label Nov 13, 2024

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Endless recursion in repr of asyncio.Future if a callback uses the Future itself as argument #93837

Endless recursion in repr of asyncio.Future if a callback uses the Future itself as argument #93837

usiems commented Jun 15, 2022

kumaraditya303 commented Jun 15, 2022 •

edited

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usiems commented Jun 15, 2022

usiems commented Jun 15, 2022

kumaraditya303 commented Jul 12, 2022 •

edited

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usiems commented Jul 13, 2022

kumaraditya303 commented Jul 13, 2022

usiems commented Aug 5, 2022

asvetlov commented Nov 12, 2024

freakboy3742 commented Nov 13, 2024

asvetlov commented Nov 13, 2024

Endless recursion in repr of asyncio.Future if a callback uses the Future itself as argument #93837

Endless recursion in repr of asyncio.Future if a callback uses the Future itself as argument #93837

Comments

usiems commented Jun 15, 2022

kumaraditya303 commented Jun 15, 2022 • edited Loading

usiems commented Jun 15, 2022

usiems commented Jun 15, 2022

kumaraditya303 commented Jul 12, 2022 • edited Loading

usiems commented Jul 13, 2022

kumaraditya303 commented Jul 13, 2022

Footnotes

usiems commented Aug 5, 2022

asvetlov commented Nov 12, 2024

freakboy3742 commented Nov 13, 2024

asvetlov commented Nov 13, 2024

kumaraditya303 commented Jun 15, 2022 •

edited

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kumaraditya303 commented Jul 12, 2022 •

edited

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