bug#46494: 28.0.50; [native-comp] Problems with async background compile

[Andy Moreton <andrewjmoreton@gmail.com>]

On Sat 20 Feb 2021, Eli Zaretskii wrote:

> OK, I've reviewed the code which kills subprocesses when Emacs is shut
> down, and I have some questions:
>
>   . How does libgccjit handle the case that its process is exiting?
>     Does it have any atexit handlers or static destructors?  IOW, how
>     does it ensure its own subprocesses, like gas etc. are terminated?
>
>   . When we invoke Emacs in a subprocess to do the async compilation,
>     do we specify that it should be killed without query?  I don't see
>     this in the code (did I miss it?), but if we don't, then exiting
>     Emacs will ask the user whether to kill the subprocesses -- does
>     it?
>
> Andy, if instead if exiting Emacs, you use signal-process, like this:
>
>   M-: (signal-process PROC-ID 'SIGHUP) RET
>
> (where PROC-ID is the process ID of the Emacs subprocess running the
> native compilation), do you see the same crash, or does the subprocess
> exit cleanly?  To see the PROC-ID, you can use the Task manager or the
> 'pslist' command from the PsTools suite.

I tried that by adding binding this to a key:
  (defun signal-hup (proc)
    (interactive "nProcess: ")
    (signal-process proc 'SIGHUP))

On a x86_64-w64-mingw32 build, sending SIGHUP to a compilation
subprocess results in the emacs abort dialog being shown briefly and
then disappearing (without user interaction). That dialog should require
pressing a button to dismiss it.

    AndyM