[issue39241] Popen of python3.6 hangs on os.read(errpipe_read, 50000)

[Irit Katriel]

Irit Katriel  added the comment:

I'm closing this because 

1. both 2.7 and 3.6 are no longer maintained
2. This is not an actual bug report (we don't know what the hanging code was 
doing) so there is no chance of reproducing it.

If you are having problems with this in a current version (>= 3.8) please 
create a new issue with a reproducible example of failing code.

If you need debugging assistance, python-list might be a more appropriate place 
than the bug tracker to ask for that.

--
nosy: +iritkatriel
resolution:  -> not a bug
stage:  -> resolved
status: open -> closed

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[issue39241] Popen of python3.6 hangs on os.read(errpipe_read, 50000)

[STINNER Victor]

STINNER Victor  added the comment:

I have no clue. Try to attach a debugger and try to inspect the Python frames. 
You can use gdb with python-gdb.py for that, for example. Or play with 
faulthandler, especially faulthandler.dump_traceback_later().

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[issue39241] Popen of python3.6 hangs on os.read(errpipe_read, 50000)

[Xu]

Xu  added the comment:

Thanks Stinner.

Do you have some clues about this issue ?
In my case, our test system use Popen to start a few infrastructure processes 
for tests going. After tests done we will kill all processes and start again 
for new round.

Most of time it works fine.  However we have some chances where one Popen hangs 
on "os.read(errpipe_read, 5) forever.

The close_fd is always true.

I guess there is some subtle issue here.

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[issue39241] Popen of python3.6 hangs on os.read(errpipe_read, 50000)

[STINNER Victor]

STINNER Victor  added the comment:

os.pipe() creates non-inheritable file descriptors by default, see PEP 446:

$ python3.6
Python 3.6.9 (default, Jul 26 2019, 00:00:00) 
>>> import os
>>> a,b=os.pipe()
>>> os.get_inheritable(a)
False
>>> os.get_inheritable(b)
False

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nosy: +vstinner

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[issue39241] Popen of python3.6 hangs on os.read(errpipe_read, 50000)

[Xu]

New submission from Xu :

I have a piece code hangs on os.read(errpipe_read, 5)
So I compared the python3.6 with python2.7 on _execute_child, I saw:

for python2.7 we create the errpipe_read/write with pipe_cloexec()

1213 # For transferring possible exec failure from child to parent
1214 # The first char specifies the exception type: 0 means
1215 # OSError, 1 means some other error.
1216 errpipe_read, errpipe_write = self.pipe_cloexec()


while for python3.6 we create the errpipe_read/write with pipe()

1251 # For transferring possible exec failure from child to parent.
1252 # Data format: "exception name:hex errno:description"
1253 # Pickle is not used; it is complex and involves memory 
allocation.
1254 errpipe_read, errpipe_write = os.pipe()

Does that mean python3.6 doesn't set the the flag FD_CLOEXEC on the pipe ?

--
components: Library (Lib)
messages: 359486
nosy: liuxu1005
priority: normal
severity: normal
status: open
title: Popen of python3.6 hangs on os.read(errpipe_read, 5)
versions: Python 3.6

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