Re: master 2c79a8f 2/2: Use posix_spawn if possible.

[Saulius Menkevicius]

I did a bit more investigation (and still don't have a reproduction vehicle) but it seems the problem has to do with signals (SIGCHLD in particular) rather than stdio redirection.

Stack trace in the child process shows it has launched a subprocess which has since exited but the child did not receive (?) SIGCHLD and appears to be blocked.

Dotnet stack trace is

[bob@fedora emacs]$ dotnet stack report -p 53193
Thread (0xCFC9):
  [Native Frames]
  System.Private.CoreLib!System.Threading.WaitHandle.WaitOneNoCheck(int32)
  System.Private.CoreLib!System.Threading.WaitHandle.WaitOne(int32)
  System.Diagnostics.Process!System.Diagnostics.ProcessWaitState.WaitForExit(int32)
  System.Diagnostics.Process!System.Diagnostics.Process.WaitForExitCore(int32)
  Microsoft.Build.Locator!Microsoft.Build.Locator.DotNetSdkLocationHelper+<GetDotNetBasePaths>d__5.MoveNext()
  Microsoft.Build.Locator!Microsoft.Build.Locator.DotNetSdkLocationHelper+<GetInstances>d__4.MoveNext()
  Microsoft.Build.Locator!Microsoft.Build.Locator.MSBuildLocator+<GetInstances>d__20.MoveNext()
  System.Linq!System.Linq.Enumerable.TryGetFirst(class System.Collections.Generic.IEnumerable`1<!!0>,bool&)
  System.Linq!System.Linq.Enumerable.FirstOrDefault(class System.Collections.Generic.IEnumerable`1<!!0>)
  Microsoft.Build.Locator!Microsoft.Build.Locator.MSBuildLocator.RegisterDefaults()
  CSharpLanguageServer!CSharpLanguageServer.Program.entry(class System.String[])

Where "ps axl" shows there is a zombie process waiting to be collected but is not.

0  1000   53193   53129  20   0 3437284 59416 -     Ssl  ?          0:00 /home/bob/src/csharp-language-server/src/CSharpLanguageServer/bin/Debug/net6.0/CSharpLanguageServer
0  1000   53203   53193  20   0      0     0 -      Z    ?          0:00 [dotnet] <defunct>

Related emacs src/callproc.cs has code that has this comment:

/* Stop blocking SIGCHLD in the child.  */

But I really don't know what should I do to attempt to fix this/find the cause.

-Saulius

Am 29.01.22 um 10:26 schrieb Eli Zaretskii:

> > From: Matt Armstrong <matt@rfc20.org>
> > Cc: p.stephani2@gmail.com, alan@idiocy.org, mituharu@math.s.chiba-u.ac.jp,
> >  emacs-devel@gnu.org
> > Date: Fri, 28 Jan 2022 09:12:22 -0800
> >
> > Eli Zaretskii <eliz@gnu.org> writes:
> >
> > > > To actually figure that out I would need to build a minimal test fixture 
> > > > for this bug/issue and submit to dotnet/runtime repo on github for them 
> > > > to check and/or fix it.
> > > >           
> > > I think there's no way around this.  We need at least to understand
> > > what part of posix_spawn code interferes with pipe-based I/O used by
> > > these LSP servers, and why.
> > >         
> > I don't find an emacs bug filed for this issue.  Saulius, it would be
> > good to file one.
> >
> > This issue tickled a memory I had of Python moving away from posix_spawn
> > due to various portability issues: https://bugs.python.org/issue35823.
> > The issues they ran into and solved may inform this investigation.
> >       
> Thanks.
>
> I see nothing there about C#, nor even about problems with stdio
> redirection in subprocesses.  There's some reference to closing file
> descriptors above 2, but AFAIU the problems in this bug report are
> related to descriptors that aren't above 2.
>