Re: SIGCHLD in vfork child context

[YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp>]

>>>>> On Sat, 13 May 2017 14:41:59 +0900, YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp> said:

> Recently Emacs on Darwin has changed to use vfork rather than fork
> for performance reasons (Bug#26397).  The latest Mac port contains a
> similar change, but I received a report telling that this causes
> occasional hangs.

> It seems that calling waitpid from the SIGCHLD handler results in
> ECHILD in the vfork child context, and in this case, Emacs aborts
> and then hangs in such a context for some reason on macOS.

> I made a patch below to avoid calling the SIGCHLD handler on Darwin,
> but I wonder if this can also be meaningful in other platforms.
> WDYT?

The original reporter could come up with a procedure to reproduce:

1. Enter (call-process-region "abc" nil "cat" nil 0) in *scratch*
2. C-x ( C-x C-e C-x ) to define a macro that evaluates that form
3. C-u 2000 C-x e to evaluate the form 2000 times

I could reproduce the hang on macOS, but not on GNU/Linux.  Could
other platform users try it to see if the patch for Darwin is also
meaningful there?


				     YAMAMOTO Mitsuharu
				mituharu@math.s.chiba-u.ac.jp