patchbots meet segmentation fault

[Frédéric Chapoton]

Dear all, help is required to fix the following issue.

At least two patchbots, one Linux and one MacOs, meet a failure related to pexpect interface for singular, namely:

sage -t --long --random-seed=0 src/sage/interfaces/singular.py  # Killed due to segmentation fault

The tested file also fails when run alone, but the copy-pasted test works fine.

Frédéric

PS : for full logs, see

https://patchbot.sagemath.org/log/0/Darwin/Darwin%20Kernel%20Version%2018.5.0:%20Mon%20Mar%2011%2020:40:32%20PDT%202019;%20root:xnu-4903.251.3~3/RELEASE_X86_64/x86_64/18.5.0/steenrod/2020-11-07%2019:50:32?short

https://patchbot.sagemath.org/log/0/Linux/57-Ubuntu_SMP_Thu_Oct_15_10:57:00_UTC_2020/x86_64/5.4.0-52-generic/petitbonum/2020-11-07%2020:48:10?short

[Dima Pasechnik]

the test (I saw this test failing before) in question is some kind of hack:

sage: try:
alarm(0.5)
singular._expect_expr('>') # interrupt this
except KeyboardInterrupt:
pass ## line 505 ##
Control-C pressed. Interrupting Singular. Please wait a few seconds...
sage: 2*a ## line 514 ##
------------------------------------------------------------------------
/home/chapoton/sage/local/lib/python3.8/site-packages/cysignals/signals.cpython-38-x86_64-linux-gnu.so(+0x7df4)[0x7f7c33af8df4]
....

perhaps a kind of race condition - I don't want to think what happens
if Control-C does not propagate quickly enough to suspend
Singular.

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[Frédéric Chapoton]

Thanks. I agree. So what to do ? Remove the doctest ? Change the alarm(0.5) ? One should probably open a ticket..

[Dima Pasechnik]

On Sun, Nov 22, 2020 at 10:12 AM Frédéric Chapoton <fchap...@gmail.com> wrote:
>
> Thanks. I agree. So what to do ? Remove the doctest ? Change the alarm(0.5) ?

if you can reproduce this locally, perhaps you can try increasing 0.5
and see if it makes a difference.

> One should probably open a ticket..

right.

> To view this discussion on the web visit https://groups.google.com/d/msgid/sage-devel/6d949ff6-3fac-4436-be17-9e466f19424bn%40googlegroups.com.

[Frédéric Chapoton]

I made https://trac.sagemath.org/ticket/30945