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Date:	Tue, 11 Aug 2020 13:59:48 +0900
To:	cygwin AT cygwin DOT com
Subject:	Re: Race condition hangs on multiple mintty/tcsh? Brad Wetmore
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From:	Takashi Yano via Cygwin <cygwin AT cygwin DOT com>
Reply-To:	Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>
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Hi Thomas,

On Thu, 6 Aug 2020 15:31:24 +0200
Thomas Wolff wrote:
> Am 06.08.2020 um 13:46 schrieb Thomas Wolff:
> > Am 06.08.2020 um 01:23 schrieb Kevin Schnitzius via Cygwin:
> >> On Wednesday, August 5, 2020, 06:56:48 PM EDT, Thomas Wolff=20
> >> <towo AT towo DOT net> wrote:
> >>> Am 04.08.2020 um 12:02 schrieb Thomas Wolff:
> >>>> Am 04.08.2020 um 00:13 schrieb Brad Wetmore via Cygwin:
> >>>>> Hi,
> >>>>>
> >>>>> I generally kick off multiple (10) mintty sessions, and place the=
m
> >>>>> around the screen.
> >>>>>
> >>>>> C:/cygwin64/bin/mintty.exe -i /Cygwin-Terminal.ico \
> >>>> --position @3 --position 120,0 --size 80x71 /bin/tcsh &
> >>>>> C:/cygwin64/bin/mintty.exe -i /Cygwin-Terminal.ico \
> >>>>> --position @3 --position 715,0 --size 80x45 /bin/tcsh &
> >>>>> C:/cygwin64/bin/mintty.exe -i /Cygwin-Terminal.ico \
> >>>>> --position @3 --position 715,660 --size 80x24 /bin/tcsh &
> >>>>>
> >>>>> Within the last 6 months or so, about 2-3 of them would hang and
> >>>>> either mintty/tcsh would not start. I put a "sleep 1" in between =
each
> >>>>> invocation and that seemed to take care of it.
> >>>>>
> >>>>> With the latest cygwin update, about 8 of them just hang even wit=
h
> >>>>> the sleep 1. I put in a "sleep 2", and now everything is coming u=
p
> >>>>> again.
> >>>>>
> >>>>> Not sure if this is a mintty or tcsh issue, but just wondering if
> >>>>> others are seeing this before I start trying to debug this.
> >>>> I can reproduce such behaviour with /bin/bash (easy cross-check), =
and
> >>>> in fact the shell is running in that case (easy test via `echo >
> >>>> .log`), so I have a vague and unpleasant suspicion it might in fac=
t be
> >>>> related to mintty although I have no idea how that would happen. T=
o be
> >>>> analysed.
> >>> When in this state, on the pty from which mintty receives child pro=
cess
> >>> output, select() does not report a ready for reading condition;=20
> >>> could it
> >>> be related to the recent poll/select patch? I could not reproduce i=
t in
> >>> cygwin 3.0.7.
> >> for i in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 ; do=20
> >> mintty=C2=A0 -i /Cygwin-Terminal.ico=C2=A0 --position @3 --position =
120,$i=20
> >> --size 80x24 /bin/bash & done
> >>
> >> This does not fail for me.=C2=A0 Nor does it fail from cmd or powers=
hell=20
> >> using a script.
> >>
> >> I tried 3.1.4 and 3.1.6 on Windows 10.=C2=A0 I tried up to 100 insta=
nces=20
> >> of of mintty...
> > Thanks for testing. It is in fact hard to reproduce, maybe also=20
> > depending on system load (speculating).
> > I could reproduce one case of one of three terminals being=20
> > unresponsive also with xterm.
> And it also happens if I drop select() from mintty (and use just=20
> non-blocking read()).
> > Does anybody familiar with pty/select or recent changes have any idea=
?

I looked into this problem. After much struggle, I think
I have found a workaround for this issue.

I am not sure why this solves the issue at all, however,
this works for me.

Could you please test a patch attached?

--=20
Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>

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