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Re: Can't read stdout of bash with GSubprocess on MSYS2




We have a helper that does questionable things during the spawning
process on Win32. This second helper is likely to be what's broken
under MSYS2.

See https://git.gnome.org/browse/glib/tree/glib/gspawn-win32.c#n22

On Mon, Sep 28, 2015 at 12:33 AM, Gang Chen <gang.chen.cn@xxxxxxxxx> wrote:
> Yes, I suspect MSYS2 or bash does something special because other console
> applications work well. I wrote a program using the GLib spawn function and
> GIOChannel, and observed the same behavior. The read function got a G_IO_HUP
> signal without any data read, when bash exited.
>
> 2015-09-28 13:27 GMT+08:00 LRN <lrn1986@xxxxxxxxx>:
>>
>> On 28.09.2015 5:01, Gang Chen wrote:
>> > Hi,
>> > I'm writing a GTK+ application with MINGW-W64, which spawns a subprocess
>> > running bash to execute some commands with GSubprocess and reads stdout
>> > of
>> > bash (installed from MSYS2). I found that if compiled without
>> > "-mwindows"
>> > compilation option the main process can read the stdout, while with
>> > "-mwindows", the read function always returns 0 bytes read. If the main
>> > process runs a normal console program, or like "mingw32/bin/gcc.exe",
>> > then
>> > it can read stdout even if compiled with "-mwindows".
>>
>> Might have something to do with what Cygwin/MSYS2 does to its
>> stdout/stderr
>> handles on initialization (as opposed to normal W32 applications).
>>
>> You could also try to write a pure-W32 API application that does this
>> (spawns different child processes with stdout/stderr redirected to pipes,
>> reads from the pipes; read g_win32_input_stream_* functions to see which
>> W32 API or C Runtime functions are used by glib to create pipes and read
>> from them) to diagnose the problem with Cygwin/MSYS2 without involving
>> glib. If you manage to do so and if the problem does affect non-glib-based
>> main process spawning bash (but not gcc), you can direct your question to
>> Cygwin and/or MSYS2 developers. If the problem only affects glib-based
>> main
>> process, try to put a breakpoint on g_win32_input_stream_read() (assuming
>> you have debug info for glib) and see what it does, and how it works
>> differently depending on what kind of child process you are running.
>>
>> --
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>>
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-- 
  Jasper
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