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

[Saulius Menkevicius <sauliusmenkevicius@fastmail.com>]

Thanks Robert!

I applied your patch and that has actually has fixed the issue. So I 
suggest this patch be applied on master.

-Saulius

Am 01.02.22 um 11:59 schrieb Robert Pluim:
>>>>>> On Mon, 31 Jan 2022 22:48:33 +0200, Saulius Menkevicius <sauliusmenkevicius@fastmail.com> said:
>      Saulius> I did a bit more investigation (and still don't have a reproduction
>      Saulius> vehicle) but it seems the problem has to do with signals (SIGCHLD in
>      Saulius> particular) rather than stdio redirection.
>
>      Saulius> Stack trace in the child process shows it has launched a subprocess
>      Saulius> which has since exited but the child did not receive (?) SIGCHLD and
>      Saulius> appears to be blocked.
>
>      Saulius> Dotnet stack trace is
>
>      Saulius> |[bob@fedora emacs]$ dotnet stack report -p 53193 Thread (0xCFC9):
>      Saulius>  [Native Frames]
>      Saulius>  System.Private.CoreLib!System.Threading.WaitHandle.WaitOneNoCheck(int32)
>      Saulius>  System.Private.CoreLib!System.Threading.WaitHandle.WaitOne(int32)
>      Saulius>  System.Diagnostics.Process!System.Diagnostics.ProcessWaitState.WaitForExit(int32)
>      Saulius>  System.Diagnostics.Process!System.Diagnostics.Process.WaitForExitCore(int32)
>      Saulius>  Microsoft.Build.Locator!Microsoft.Build.Locator.DotNetSdkLocationHelper+<GetDotNetBasePaths>d__5.MoveNext()
>      Saulius>  Microsoft.Build.Locator!Microsoft.Build.Locator.DotNetSdkLocationHelper+<GetInstances>d__4.MoveNext()
>      Saulius>  Microsoft.Build.Locator!Microsoft.Build.Locator.MSBuildLocator+<GetInstances>d__20.MoveNext()
>      Saulius>  System.Linq!System.Linq.Enumerable.TryGetFirst(class
>      Saulius>  System.Collections.Generic.IEnumerable`1<!!0>,bool&)
>      Saulius>  System.Linq!System.Linq.Enumerable.FirstOrDefault(class
>      Saulius>  System.Collections.Generic.IEnumerable`1<!!0>)
>      Saulius>  Microsoft.Build.Locator!Microsoft.Build.Locator.MSBuildLocator.RegisterDefaults()
>      Saulius>  CSharpLanguageServer!CSharpLanguageServer.Program.entry(class
>      Saulius>  System.String[]) |
>
>      Saulius> Where "ps axl" shows there is a zombie process waiting to be collected
>      Saulius> but is not.
>
>      Saulius> |0 1000 53193 53129 20 0 3437284 59416 - Ssl ? 0:00
>      Saulius>  /home/bob/src/csharp-language-server/src/CSharpLanguageServer/bin/Debug/net6.0/CSharpLanguageServer
>      Saulius>  0 1000 53203 53193 20 0 0 0 - Z ? 0:00 [dotnet] <defunct> |
>
>
>      Saulius> Related emacs src/callproc.cs has code that has this comment:
>
>      Saulius> /* Stop blocking SIGCHLD in the child.  */
>
>      Saulius> But I really don't know what should I do to attempt to fix this/find
>      Saulius> the cause.
>
> Despite the comment, that code doesnʼt actually unblock SIGCHLD, it
> just sets the child mask to be the same as the parent, and SIGCHLD and
> SIGINT are blocked in the parent at this point.
>
> Try the following:
>
> diff --git a/src/callproc.c b/src/callproc.c
> index 4d3b0bb8e0..2b4e8977a3 100644
> --- a/src/callproc.c
> +++ b/src/callproc.c
> @@ -1378,6 +1378,12 @@ emacs_posix_spawn_init_attributes (posix_spawnattr_t *attributes)
>     /* Stop blocking SIGCHLD in the child.  */
>     sigset_t oldset;
>     error = pthread_sigmask (SIG_SETMASK, NULL, &oldset);
> +  if (error != 0)
> +    goto out;
> +  error = sigdelset (&oldset, SIGCHLD);
> +  if (error != 0)
> +    goto out;
> +  error = sigdelset (&oldset, SIGINT);
>     if (error != 0)
>       goto out;
>     error = posix_spawnattr_setsigmask (attributes, &oldset);