[issue44887] test_input_tty hangs when run multiple times in the same process on macOS 10.15

[Andrei Kulakov]

Andrei Kulakov  added the comment:

I've looked into this and the hang happens on this line:

https://github.com/python/cpython/blob/de3db1448b1b983eeb9f4498d07e3d2f1fb6d29d/Lib/test/test_builtin.py#L2030

So the issue is that on the second run, there's nothing to read on that fd. 
I've tried using os.stat to check if there's data on the fd, but it returned 0 
data in both 1st and 2nd runs.

However, if a small sleep is added before running os.stat, it does return size 
of data on 1st run and returns 0 on 2nd run, meaning it's possible to avoid the 
hang and error out instead (is that an improvement?)

This is on MacOS 11.4 Big Sur by the way.

This is my test debug branch:

https://github.com/python/cpython/compare/main...akulakov:Test-check_input_tty-FIX?expand=1

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[issue44887] test_input_tty hangs when run multiple times in the same process on macOS 10.15

[STINNER Victor]

STINNER Victor  added the comment:

Is it related to https://bugs.python.org/issue41034 ?

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[issue44887] test_input_tty hangs when run multiple times in the same process on macOS 10.15

[Łukasz Langa]

Łukasz Langa  added the comment:

It *is* readline-related after all O_O

Commenting out this section in Pdb.__init__ makes the issue go away:
https://github.com/python/cpython/blob/64a7812c170f5d46ef16a1517afddc7cd92c5240/Lib/pdb.py#L234-L239


time ./python.exe -E -Wd -m test test_builtin test_builtin
0:00:00 load avg: 2.12 Run tests sequentially
0:00:00 load avg: 2.12 [1/2] test_builtin
0:00:00 load avg: 2.12 [2/2] test_builtin

== Tests result: SUCCESS ==

All 2 tests OK.

Total duration: 1.3 sec
Tests result: SUCCESS
1.56 real 1.42 user 0.10 sys


I'll be continuing on this tomorrow to find the root cause.

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[issue44887] test_input_tty hangs when run multiple times in the same process on macOS 10.15

[Łukasz Langa]

Łukasz Langa  added the comment:

The doctest runner sets an output redirecting debugger, which subclasses Pdb, 
around actually running the doctest. This action causes the hang. New finding, 
we can hang the test with test_pdb too:

$ python3.9 -m test test_pdb test_builtin -v

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[issue44887] test_input_tty hangs when run multiple times in the same process on macOS 10.15

[Łukasz Langa]

Łukasz Langa  added the comment:

I found the high-level reason why test_builtin hangs: it runs doctests as well. 
What's the root cause? I don't know yet.


But to confirm, I can also hang the tests by running:

$ python3.9 -m test test_doctest test_builtin -v


Now to discover what it is that doctest does...

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[issue44887] test_input_tty hangs when run multiple times in the same process on macOS 10.15

[Łukasz Langa]

Łukasz Langa  added the comment:

Amazingly, excluding every other test function with a bunch of `-i` patterns 
still makes it hang when ran twice. On the other hand, only including the test 
function with `-m` works fine.

This is very weird. Looking further.

Semi-relatedly, I found BPO-26228, could reproduce it, and finished an open PR 
on it. While those are separate issues, I'm hoping to solve them both.

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[issue44887] test_input_tty hangs when run multiple times in the same process on macOS 10.15

[Łukasz Langa]

Łukasz Langa  added the comment:

This might be a long-standing problem. I haven't encountered it before because 
I was always running -R: with -j and in this case the test is skipped:

test_input_tty (test.test_builtin.PtyTests) ... skipped 'stdin and stdout must 
be ttys'

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[issue44887] test_input_tty hangs when run multiple times in the same process on macOS 10.15

[Łukasz Langa]

Łukasz Langa  added the comment:

Parent process hangs on:
* thread #1, queue = 'com.apple.main-thread', stop reason = signal SIGSTOP
  * frame #0: 0x7fff6741181e libsystem_kernel.dylib`read + 10
frame #1: 0x00010226a117 python.exe`_Py_read(fd=3, 
buf=0x7f8d24009840, count=8192) at fileutils.c:1744:13
frame #2: 0x0001022f1335 
python.exe`_io_FileIO_readinto_impl(self=0x000103b284d0, 
buffer=0x7ffeedcbe928) at fileio.c:645:9
frame #3: 0x0001022f063e 
python.exe`_io_FileIO_readinto(self=0x000103b284d0, arg=0x000102f5d090) 
at fileio.c.h:205:20
frame #4: 0x0001020050e9 
python.exe`method_vectorcall_O(func=0x0001026fd970, 
args=0x7ffeedcbeaf0, nargsf=2, kwnames=0x) at 
descrobject.c:462:24
frame #5: 0x000101ff323d 
python.exe`_PyObject_VectorcallTstate(tstate=0x7f8d20d04f00, 
callable=0x0001026fd970, args=0x7ffeedcbeaf0, nargsf=2, 
kwnames=0x) at abstract.h:114:11
frame #6: 0x000101ff30c9 
python.exe`PyObject_VectorcallMethod(name=0x0001026fcbe0, 
args=0x7ffeedcbeaf0, nargsf=2, kwnames=0x) at call.c:770:24
frame #7: 0x0001022f92a0 
python.exe`PyObject_CallMethodOneArg(self=0x000103b284d0, 
name=0x0001026fcbe0, arg=0x000102f5d090) at abstract.h:204:12

where "name" in frame #7 is the "readinto" method of <_io.FileIO name=3 
mode='rb' closefd=True> and "arg" is .


Child process hangs on:

* thread #1, queue = 'com.apple.main-thread', stop reason = signal SIGSTOP
  * frame #0: 0x7fff67413bf6 libsystem_kernel.dylib`write + 10
frame #1: 0x00010226a3e0 python.exe`_Py_write_impl(fd=2, 
buf=0x7ffeedcbcbcb, count=1, gil_held=0) at fileutils.c:1813:17
frame #2: 0x00010226a535 python.exe`_Py_write_noraise(fd=2, 
buf=0x7ffeedcbcbcb, count=1) at fileutils.c:1871:12
frame #3: 0x000102257834 python.exe`_Py_DumpASCII(fd=2, 
text=0x000102a1bed0) at traceback.c:1002:13
frame #4: 0x000102258ba5 python.exe`dump_frame(fd=2, 
frame=0x0001025dbba8) at traceback.c:1035:9
frame #5: 0x0001022579fa python.exe`dump_traceback(fd=2, 
tstate=0x7f8d20d04f00, write_header=0) at traceback.c:1084:9
frame #6: 0x000102257bc6 python.exe`_Py_DumpTracebackThreads(fd=2, 
interp=0x7f8d2281b010, current_tstate=0x7f8d20d04f00) at 
traceback.c:1186:9
frame #7: 0x000102311dc3 python.exe`faulthandler_dump_traceback(fd=2, 
all_threads=1, interp=0x7f8d2281b010) at faulthandler.c:245:15
frame #8: 0x00010231224b python.exe`faulthandler_user(signum=14) at 
faulthandler.c:843:5
frame #9: 0x7fff674c85fd libsystem_platform.dylib`_sigtramp + 29
frame #10: 0x7fff6741435f libsystem_kernel.dylib`__ioctl + 11
frame #11: 0x7fff6741434b libsystem_kernel.dylib`ioctl + 150
frame #12: 0x7fff6734ad63 libsystem_c.dylib`tcsetattr + 111
frame #13: 0x000103c772ee libreadline.8.dylib`_set_tty_settings + 28
frame #14: 0x000103c76d87 libreadline.8.dylib`rl_prep_terminal + 683
frame #15: 0x000103c88ce9 libreadline.8.dylib`_rl_callback_newline + 51
frame #16: 0x000103c5ae75 
readline.cpython-311d-darwin.so`readline_until_enter_or_signal(prompt="prompt", 
signal=0x7ffeedcbd63c) at readline.c:1318:5
frame #17: 0x000103c58637 
readline.cpython-311d-darwin.so`call_readline(sys_stdin=0x7fff8d9c8d90, 
sys_stdout=0x7fff8d9c8e28, prompt="prompt") at readline.c:1396:9
frame #18: 0x000101fad9b6 
python.exe`PyOS_Readline(sys_stdin=0x7fff8d9c8d90, 
sys_stdout=0x7fff8d9c8e28, prompt="prompt") at myreadline.c:391:14
frame #19: 0x0001021a071d 
python.exe`builtin_input_impl(module=0x00010268c0b0, 
prompt=0x0001027a0400) at bltinmodule.c:2188:13

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[issue44887] test_input_tty hangs when run multiple times in the same process on macOS 10.15

[Łukasz Langa]

Łukasz Langa  added the comment:

Hynek confirmed on Big Sur with Python 3.9.5 from asdf that test_input_tty 
hangs, too, if ran for the second time in the same process.

Moreover, readline is not it. First of all, it's libedit on macOS:

❯ ll /usr/lib/libreadline.dylib
lrwxr-xr-x  1 root  wheel15B Feb  2  2020 /usr/lib/libreadline.dylib -> 
libedit.3.dylib


So Python uses that by default:
>>> import readline
>>> readline._READLINE_LIBRARY_VERSION
'EditLine wrapper'
>>> readline._READLINE_RUNTIME_VERSION
1026
>>> readline._READLINE_VERSION
1026


Unless you instruct it to use readline (for example by providing "-I$(brew 
--prefix readline)/include" to CFLAGS and "-L$(brew --prefix readline)/lib" to 
LDFLAGS before running ./configure):
>>> import readline
>>> readline._READLINE_LIBRARY_VERSION
'8.1'
>>> readline._READLINE_RUNTIME_VERSION
2049
>>> readline._READLINE_VERSION
2049


The hang is the same in both cases. 


Next course of action, checking if it's not due to fork shenanigans in 
_run_child():

https://github.com/python/cpython/blob/1841c70f2bdab9d29c1c74a8afffa45daf98/Lib/test/test_builtin.py#L2001

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[issue44887] test_input_tty hangs when run multiple times in the same process on macOS 10.15

[Łukasz Langa]

New submission from Łukasz Langa :

(I'm still investigating at the moment whether something changed in my 
environment.)

Running the following right now hangs on test_input_tty for me:

./python.exe -m test test_builtin test_builtin -v


This fails on all branches up to and including 3.7, so I assume this is 
environment-specific unless it's a regression due to a change that was 
backported all the way back to 3.7, which is out of the question as the last 
functional commit on 3.7 was back in June.

Things I tried so far:
- rebooting;
- using another terminal app (I use iTerm2 by default, tried Terminal.app too);
- another shell (I use fish by default, tried bash 5.0 as well);
- a non-pydebug build (I use pydebug builds by default to run -R:)


The test in question is using deadline if available and 
`sysconfig.get_config_vars()['HAVE_LIBREADLINE']` returns 1. I'll be trying to 
check if that works for me next.

--
messages: 399380
nosy: lukasz.langa
priority: low
severity: normal
stage: test needed
status: open
title: test_input_tty hangs when run multiple times in the same process on 
macOS 10.15
versions: Python 3.10, Python 3.11, Python 3.8, Python 3.9

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