* bug#18772: 24.3; Emacs deadlocks on subprocess write when read is pending
@ 2014-10-19 7:06 Haitao Zhang
2014-10-19 17:55 ` Eli Zaretskii
0 siblings, 1 reply; 4+ messages in thread
From: Haitao Zhang @ 2014-10-19 7:06 UTC (permalink / raw)
To: 18772
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I have reliably experienced UI freezes under the following conditions:
1) A large read from a subprocess is in progress (2+MBs, around 2
seconds on Windows with w32-pipe-read-delay set to 0).
2) A mid-sized write is sent to the subprocess, from a not very large source
code buffer but large enough to block the write. The subprocess will not
read from its side until it finishes the transfer started in 1.
Killing the subprocess unfreezes Emacs. The error message indicates that
Emacs blocked on the write, complaing about the process being dead while
writing. The process buffer, normally mopped up by the process filter,
is filled with text midway through the transfer, indicating that the process
filter has stopped getting called. Finally locking out the offending
blocking write while the read is still in progress has ensured that the
deadlocks no longer happen. Success of the workaround gives me
confidence that this is an Emacs bug or feature.
Reading through the Emacs source files, it appears that when user calls
process-send-* in elisp eventually Emacs calls send_process in
process.c. If the send blocks it calls wait_reading_process_output,
which in turn should read pending output. Apparently in my case this is
not happening and a deadlock occured instead. My use case has large and
large enough transfers going both ways which may be different from
typical use patterns. Also on Windows reading from the pipe is slow even
when the w32-pipe-read-delay is set to 0 which gives more opportunities
for the deadlock to happen. I note again that this happens reliably
instead of intermittently once the conditions listed above are met.
I hope this bug report will help you in improving Emacs.
Haitao Zhang
If Emacs crashed, and you have the Emacs process in the gdb debugger,
please include the output from the following gdb commands:
`bt full' and `xbacktrace'.
For information about debugging Emacs, please read the file
c:/alt/emacs/emacs-24.3/etc/DEBUG.
In GNU Emacs 24.3.1 (i386-mingw-nt6.2.9200)
of 2013-03-17 on MARVIN
Windowing system distributor `Microsoft Corp.', version 6.2.9200
Configured using:
`configure --with-gcc (4.7) --cflags
-ID:/devel/emacs/libs/libXpm-3.5.8/include
-ID:/devel/emacs/libs/libXpm-3.5.8/src
-ID:/devel/emacs/libs/libpng-dev_1.4.3-1/include
-ID:/devel/emacs/libs/zlib-dev_1.2.5-2/include
-ID:/devel/emacs/libs/giflib-4.1.4-1/include
-ID:/devel/emacs/libs/jpeg-6b-4/include
-ID:/devel/emacs/libs/tiff-3.8.2-1/include
-ID:/devel/emacs/libs/gnutls-3.0.9/include
-ID:/devel/emacs/libs/libiconv-1.13.1-1-dev/include
-ID:/devel/emacs/libs/libxml2-2.7.8/include/libxml2'
Important settings:
value of $LANG: ENU
locale-coding-system: cp1252
default enable-multibyte-characters: t
Major mode: C++/l
Minor modes in effect:
irony-mode: t
global-company-mode: t
company-mode: t
autopair-global-mode: t
autopair-mode: t
delete-selection-mode: t
cua-mode: t
recentf-mode: t
global-auto-revert-mode: t
tooltip-mode: t
mouse-wheel-mode: t
menu-bar-mode: t
file-name-shadow-mode: t
global-font-lock-mode: t
font-lock-mode: t
blink-cursor-mode: t
auto-composition-mode: t
auto-encryption-mode: t
auto-compression-mode: t
line-number-mode: t
transient-mark-mode: t
abbrev-mode: t
Recent input:
<wheel-up> <down-mouse-1> <mouse-1> <return> <tab>
i f SPC ( c a c A-H-s- h e <tab> p <tab> . A-H-s-
f <backspace> F <backspace> <backspace> . A-H-s- <down>
<down> <down> <down> <down> <down> <down> <down> <down>
<down> <down> <down> <down> <down> <down> <down> <down>
<down> <down> <down> <down> <down> <down> <down> <down>
<down> <down> <down> <down> g e t E <return> SPC =
= SPC " z i p <menu-bar> <buffer> C-a <menu-bar> <buffer>
C-a <up> <up> <up> <up> <up> <up> <up> C-a C-k C-k
<up> <up> <up> <up> C-v <down> <down> <down> <down>
<down> <down> <down> <down> <down> <down> C-k C-k <up>
<up> <up> <up> <up> <up> <up> <up> <up> <up> <up> <up>
<down> <down> C-y <up> <tab> <right> <right> <right>
<right> <right> <right> <right> <right> <right> <right>
<right> <right> <right> <right> <right> <right> <right>
<right> <right> <right> <right> <right> <right> <right>
<right> <right> <right> <right> <right> <right> <right>
<backspace> ! <right> <right> <right> <right> <right>
<right> <right> <right> <right> <left> <return> <tab>
<down> <down> C-a C-k C-k <up> <up> C-y <up> <up> <up>
<up> <return> <down> <down> <down> <right> <right>
<right> <right> <down> <down> <down> <down> <down>
<left> <left> <left> <left> <left> <left> <right> <right>
<left> <right> C-k C-k C-k C-k C-k C-k C-k C-k C-k
C-k C-k C-k C-k <up> <up> <up> <up> <up> <up> <down>
<down> <up> <up> <up> <down> C-y <up> <up> <up> <up>
<up> <up> <right> <right> <right> <right> <right> <right>
<right> <left> E d g a A-H-s- <down> <down> <return>
( u r i <right> SPC & & SPC <help-echo> <help-echo>
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo>
<help-echo> <menu-bar> <help-menu> <emacs-manual-bug>
<help-echo> <down-mouse-1> <mouse-2> <wheel-down> <double-wheel-down>
<wheel-down> <double-wheel-down> q <help-echo> <help-echo>
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo>
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo>
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo>
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo>
<menu-bar> <help-menu> <send-emacs-bug-report>
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^ permalink raw reply [flat|nested] 4+ messages in thread
* bug#18772: 24.3; Emacs deadlocks on subprocess write when read is pending
2014-10-19 7:06 bug#18772: 24.3; Emacs deadlocks on subprocess write when read is pending Haitao Zhang
@ 2014-10-19 17:55 ` Eli Zaretskii
2014-10-19 21:59 ` Haitao Zhang
0 siblings, 1 reply; 4+ messages in thread
From: Eli Zaretskii @ 2014-10-19 17:55 UTC (permalink / raw)
To: Haitao Zhang; +Cc: 18772
> Date: Sun, 19 Oct 2014 00:06:50 -0700
> From: Haitao Zhang <zhtprog@gmail.com>
>
> I have reliably experienced UI freezes under the following conditions:
> 1) A large read from a subprocess is in progress (2+MBs, around 2
> seconds on Windows with w32-pipe-read-delay set to 0).
> 2) A mid-sized write is sent to the subprocess, from a not very large source
> code buffer but large enough to block the write. The subprocess will not
> read from its side until it finishes the transfer started in 1.
>
> Killing the subprocess unfreezes Emacs. The error message indicates that
> Emacs blocked on the write, complaing about the process being dead while
> writing. The process buffer, normally mopped up by the process filter,
> is filled with text midway through the transfer, indicating that the process
> filter has stopped getting called. Finally locking out the offending
> blocking write while the read is still in progress has ensured that the
> deadlocks no longer happen. Success of the workaround gives me
> confidence that this is an Emacs bug or feature.
I'm quite sure this is bug #18420, already fixed for the upcoming
Emacs 24.4 release.
> Reading through the Emacs source files, it appears that when user calls
> process-send-* in elisp eventually Emacs calls send_process in
> process.c. If the send blocks it calls wait_reading_process_output,
> which in turn should read pending output. Apparently in my case this is
> not happening and a deadlock occured instead.
It is not happening, because until the above-mentioned fix the code
you described was not executed on Windows, because neither EWOULDBLOCK
nor EAGAIN was ever returned by writes to a pipe.
The fix made the pipes on Windows non-blocking, so now the code you
describe really is used on Windows.
That is why I suggested that you try a later binary. There are
binaries of the 24.4 pretests floating around, and if you have MinGW
and MSYS/MSYS2 installed, you should be able to build Emacs yourself.
^ permalink raw reply [flat|nested] 4+ messages in thread
* bug#18772: 24.3; Emacs deadlocks on subprocess write when read is pending
2014-10-19 17:55 ` Eli Zaretskii
@ 2014-10-19 21:59 ` Haitao Zhang
2014-10-20 2:40 ` Eli Zaretskii
0 siblings, 1 reply; 4+ messages in thread
From: Haitao Zhang @ 2014-10-19 21:59 UTC (permalink / raw)
To: Eli Zaretskii; +Cc: 18772
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Thank you for the explanation. I filed this bug report late last night
before seeing your response on the mail list. I will try to get hold a copy
of 24.4 in the near future. Please feel free to close this one. If my
problem does not go away with the new release I can reopen the ticket.
On Sun, Oct 19, 2014 at 10:55 AM, Eli Zaretskii <eliz@gnu.org> wrote:
> > Date: Sun, 19 Oct 2014 00:06:50 -0700
> > From: Haitao Zhang <zhtprog@gmail.com>
> >
> > I have reliably experienced UI freezes under the following conditions:
> > 1) A large read from a subprocess is in progress (2+MBs, around 2
> > seconds on Windows with w32-pipe-read-delay set to 0).
> > 2) A mid-sized write is sent to the subprocess, from a not very large
> source
> > code buffer but large enough to block the write. The subprocess will not
> > read from its side until it finishes the transfer started in 1.
> >
> > Killing the subprocess unfreezes Emacs. The error message indicates that
> > Emacs blocked on the write, complaing about the process being dead while
> > writing. The process buffer, normally mopped up by the process filter,
> > is filled with text midway through the transfer, indicating that the
> process
> > filter has stopped getting called. Finally locking out the offending
> > blocking write while the read is still in progress has ensured that the
> > deadlocks no longer happen. Success of the workaround gives me
> > confidence that this is an Emacs bug or feature.
>
> I'm quite sure this is bug #18420, already fixed for the upcoming
> Emacs 24.4 release.
>
> > Reading through the Emacs source files, it appears that when user calls
> > process-send-* in elisp eventually Emacs calls send_process in
> > process.c. If the send blocks it calls wait_reading_process_output,
> > which in turn should read pending output. Apparently in my case this is
> > not happening and a deadlock occured instead.
>
> It is not happening, because until the above-mentioned fix the code
> you described was not executed on Windows, because neither EWOULDBLOCK
> nor EAGAIN was ever returned by writes to a pipe.
>
> The fix made the pipes on Windows non-blocking, so now the code you
> describe really is used on Windows.
>
> That is why I suggested that you try a later binary. There are
> binaries of the 24.4 pretests floating around, and if you have MinGW
> and MSYS/MSYS2 installed, you should be able to build Emacs yourself.
>
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^ permalink raw reply [flat|nested] 4+ messages in thread
* bug#18772: 24.3; Emacs deadlocks on subprocess write when read is pending
2014-10-19 21:59 ` Haitao Zhang
@ 2014-10-20 2:40 ` Eli Zaretskii
0 siblings, 0 replies; 4+ messages in thread
From: Eli Zaretskii @ 2014-10-20 2:40 UTC (permalink / raw)
To: Haitao Zhang; +Cc: 18772-done
> Date: Sun, 19 Oct 2014 14:59:03 -0700
> From: Haitao Zhang <zhtprog@gmail.com>
> Cc: 18772@debbugs.gnu.org
>
> Thank you for the explanation. I filed this bug report late last night before
> seeing your response on the mail list. I will try to get hold a copy of 24.4 in
> the near future. Please feel free to close this one. If my problem does not go
> away with the new release I can reopen the ticket.
OK, closing.
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2014-10-20 2:40 UTC | newest]
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-- links below jump to the message on this page --
2014-10-19 7:06 bug#18772: 24.3; Emacs deadlocks on subprocess write when read is pending Haitao Zhang
2014-10-19 17:55 ` Eli Zaretskii
2014-10-19 21:59 ` Haitao Zhang
2014-10-20 2:40 ` Eli Zaretskii
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