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

[Saulius Menkevicius <sauliusmenkevicius@fastmail.com>]

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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.

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