Re: gdb fails to flush output (msys2)

[Juan José García-Ripoll]

I am not sure this has to do with using spawn() which IMHO would also
benefit Windows as compared to faking fork(). To confirm this, I have
run emacs and gdb inside Process Explorer. Just before I enter "run" in
the "gdb" window, Process Explorer shows a total of 30kb written by gdb,
while after my process is finished it shows 32kb. Those extra 2kb are
not shown by Emacs.

Below I show a complete interaction consisting on four steps: (1) launch
gdb with M-x gdb, supplying "c:/msys64/ucrt64/bin/gdb -i=mi
c:/home/juanjo/src/tensor/build-msys2-ucrt64/tests/test_rand.exe", (2)
enter "run" + enter in gdb, (3) press again <enter>, (4) press <enter>,
(5) type "quit" follwed by <enter>. Note how Emacs fails to show me the
output of the debugger and interprets a single <enter> as pressing "run"
again. Between steps (1) and (2), Process Explorer shows 2k of written
data, after (3) it shows another 2k.

Current directory is c:/home/juanjo/src/tensor/build-msys2-ucrt64/tests/
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Reading symbols from 
c:/home/juanjo/src/tensor/build-msys2-ucrt64/tests/test_rand.exe...
(gdb) run <<<< Step (2)
Starting program: 
c:\home\juanjo\src\tensor\build-msys2-ucrt64\tests\test_rand.exe 
[New Thread 17312.0x144c]
[New Thread 17312.0x1f28]
[New Thread 17312.0x4d0]
<<< Step (3), press <enter>
[[----------] Global test environment set-up.
[----------] 10 tests from RandTest
[ RUN      ] RandTest.IntSize
[       OK ] RandTest.IntSize (0 ms)
[ RUN      ] RandTest.LongSize
[       OK ] RandTest.LongSize (0 ms)
[ RUN      ] RandTest.Reseed
[       OK ] RandTest.Reseed (1 ms)
[ RUN      ] RandTest.DoubleBalanced
[       OK ] RandTest.DoubleBalanced (0 ms)
[ RUN      ] RandTest.DoubleSigma
[       OK ] RandTest.DoubleSigma (1 ms)
[ RUN      ] RandTest.ComplexBalanced
[       OK ] RandTest.ComplexBalanced (1 ms)
[ RUN      ] RandTest.ComplexUncorrelated
[       OK ] RandTest.ComplexUncorrelated (0 ms)
[ RUN      ] RandTest.IntEmpty
[       OK ] RandTest.IntEmpty (0 ms)
[ RUN      ] RandTest.LongEmpty
[       OK ] RandTest.LongEmpty (0 ms)
[ RUN      ] RandTest.ULongEmpty
[       OK ] RandTest.ULongEmpty (0 ms)
[----------] 10 tests from RandTest (3 ms total)

[----------] Global test environment tear-down
[[  PASSED  ] 10 tests.
[Thread 17312.0x1f28 exited with code 0]
[Thread 17312.0x4d0 exited with code 0]
[Thread 17312.0x144c exited with code 0]
[Inferior 1 (process 17312) exited normally]
(gdb) Starting program: 
c:\home\juanjo\src\tensor\build-msys2-ucrt64\tests\test_rand.exe 
[New Thread 18700.0xdf8]
[New Thread 18700.0x18f4]
[New Thread 18700.0xf08]
[<<< Step (4), press <enter>
[----------] Global test environment set-up.
[----------] 10 tests from RandTest
[ RUN      ] RandTest.IntSize
[       OK ] RandTest.IntSize (0 ms)
[ RUN      ] RandTest.LongSize
[       OK ] RandTest.LongSize (0 ms)
[ RUN      ] RandTest.Reseed
[       OK ] RandTest.Reseed (1 ms)
[ RUN      ] RandTest.DoubleBalanced
[       OK ] RandTest.DoubleBalanced (0 ms)
[ RUN      ] RandTest.DoubleSigma
[       OK ] RandTest.DoubleSigma (2 ms)
[ RUN      ] RandTest.ComplexBalanced
[       OK ] RandTest.ComplexBalanced (0 ms)
[ RUN      ] RandTest.ComplexUncorrelated
[       OK ] RandTest.ComplexUncorrelated (1 ms)
[ RUN      ] RandTest.IntEmpty
[       OK ] RandTest.IntEmpty (0 ms)
[ RUN      ] RandTest.LongEmpty
[       OK ] RandTest.LongEmpty (0 ms)
[ RUN      ] RandTest.ULongEmpty
[       OK ] RandTest.ULongEmpty (0 ms)
[----------] 10 tests from RandTest (4 ms total)

[----------] Global test environment tear-down
[[  PASSED  ] 10 tests.
[Thread 18700.0xf08 exited with code 0]
[Thread 18700.0xdf8 exited with code 0]
[Thread 18700.0x18f4 exited with code 0]
[Inferior 1 (process 18700) exited normally]
(gdb) Starting program: 
c:\home\juanjo\src\tensor\build-msys2-ucrt64\tests\test_rand.exe 
[New Thread 12752.0x21b4]
[New Thread 12752.0x3710]
[New Thread 12752.0x4934]
[quit<<< Step (4)

Debugger finished


Jostein Kjønigsen <jostein@secure.kjonigsen.net> writes:
> On 15.03.2022 10:58, Juan José García-Ripoll wrote:
>
>  Eli Zaretskii <eliz@gnu.org> writes:
>
>  Can you show how that program behaves when invoked from the system
> shell, not under the debugger?  Also, if you invoke "M-x shell" inside
> Emacs, and then run that program from the inferior shell, does it
> behave correctly, or does it also hangs until you type Enter?
>
>
> Let me summarize all the questions in this single post. What is related
> to MSYS2 is the use of MSYS2's toolchains for building and debugging the
> software. There is nothing specific to MSYS2 other than specifying to
> Emacs that the debugger is c:/msys64/ucrt64/bin/gdb.exe or some other
> program from the toolchain I choose.
>
> Your paragraph abore is quite on spot. As I stated before, if I use M-x
> shell and invoke the debugger from the shell (still within Emacs)
> everything works just fine, so it is not a buffering issue. Also, to be
> more precise, within the debugger the program runs to completion, which
> means the output is completely unbuffered. It therefore should have been
> shown by Emacs' gdb already when I copied the text.
>
> Another indication that there is some problem with Emacs' GDB/GUD
> packages is that the output _is_ there. If I type a command right after
> the last shown output, gdb executes that command, and any following one,
> but re-displays the original output of the program again and again. It
> is somehow as if it had reinterpreted the program's output as a prompt.
>
> Is there a way I can debug how GUD is behaving or interfacing with gdb's
> output? I know some other major modes keep debugging information or
> intermediate buffers if requested. But I still have not found it for
> GUD.
>
> Best,
>
> Could this error in any way be related to the previous issue with had with 
> "use posix_spawn"? [1]
>
> For those who need a reminder, as far as I understood it, the key issue there 
> was that  a required bugfix for
> Mac (but also generally an optimization) was made into a default optimization 
> for platforms, and the idea was
> that unless it was proven troublesome one could decide to keep it.
>
> Well, on Linux it did cause some issues with triggering external processes. 
> Specifically .NET-based tooling,
> made especially painful with .NET-based Language Server implementations no 
> longer working (C# and F#).
>
> If this is another instance of such a bug (and I'm deliberately qualifing 
> that with an "if"), would it make sense
> to reverse this optimization on all platforms not Mac? There seems to be 
> several unintended side-effects, and
> could possibly be more?
>
> [1] https://lists.gnu.org/archive/html/emacs-devel/2022-01/msg01561.html

-- 
Juan José García Ripoll
http://juanjose.garciaripoll.com
http://quinfog.hbar.es