Re: Support open-process and friends on MS-Windows

[Eli Zaretskii <eliz@gnu.org>]

> From: Andy Wingo <wingo@pobox.com>
> Cc: ludo@gnu.org (Ludovic Courtès),  guile-devel@gnu.org
> Date: Sat, 25 Jun 2016 16:43:34 +0200
> 
> > @@ -659,7 +663,7 @@ SCM_DEFINE (scm_kill, "kill", 2, 0, 0,
> >  #else
> >    /* Mingw has raise(), but not kill().  (Other raw DOS environments might
> >       be similar.)  Use raise() when the requested pid is our own process,
> > -     otherwise bomb.  */
> > +     otherwise TerminateProcess.  */
> >    if (scm_to_int (pid) == getpid ())
> >      {
> >        if (raise (scm_to_int (sig)) != 0)
> > @@ -673,6 +677,10 @@ SCM_DEFINE (scm_kill, "kill", 2, 0, 0,
> >            goto err;
> >          }
> >      }
> > +#ifdef __MINGW32__
> > +  if (w32_kill_proc (scm_to_int (pid), scm_to_int (sig)) != 0)
> > +    SCM_SYSERROR;
> > +#endif	/* __MINGW32__ */
> >  #endif
> >    return SCM_UNSPECIFIED;
> >  }
> 
> Here we effectively have two mingw blocks.  Can the previous one be
> removed?

The previous block is not MinGW-specific.  It allows any system that
has 'raise' (which is Standard C, so should be available everywhere)
to at least kill the current process.  This code was there before my
changes, and I saw no reasons to remove it.

> If not, let's fold it into `w32_kill_proc', and in any case
> let's rename `w32_kill_proc' to `kill', and then define HAVE_KILL.

I didn't want to call the function 'kill', as some other linked-in
library might have it, and then you'd have a clash.  'kill' is too
simple a name to overload.

> > @@ -1141,7 +1143,7 @@ SCM_DEFINE (scm_execl, "execl", 1, 0, 1,
> >  
> >    exec_argv = scm_i_allocate_string_pointers (args);
> >  
> > -  execv (exec_file, exec_argv);
> > +  execv (exec_file, (char const * const *)exec_argv);
> >    SCM_SYSERROR;
> >  
> >    /* not reached.  */
> 
> make[3]: Entering directory '/home/wingo/src/guile-2.0/libguile'
>   CC       libguile_2.0_la-posix.lo
> posix.c: In function 'scm_execl':
> posix.c:1146:21: warning: passing argument 2 of 'execv' from incompatible pointer type [-Wincompatible-pointer-types]
>    execv (exec_file, (char const * const *)exec_argv);
>                      ^
> In file included from ../lib/unistd.h:40:0,
>                  from posix.c:50:
> /home/wingo/.guix-profile/include/unistd.h:566:12: note: expected 'char * const*' but argument is of type 'const char * const*'
>  extern int execv (const char *__path, char *const __argv[])
>             ^~~~~
> 
> What should be done here?

Make the cast MinGW-only?

> > @@ -1408,16 +1433,16 @@ scm_open_process (SCM mode, SCM prog, SCM args)
> >    if (err > 0)
> >      {
> >        char *msg = strerror (errno);
> > -      fprintf (fdopen (err, "a"), "In execlp of %s: %s\n",
> > +      fprintf (fdopen (err, "a"), "In execvp of %s: %s\n",
> >                 exec_file, msg);
> >      }
> >  
> >    _exit (EXIT_FAILURE);
> > +#endif	/* HAVE_FORK */
> >    /* Not reached.  */
> >    return SCM_BOOL_F;
> >  }
> >  #undef FUNC_NAME
> > -#endif /* HAVE_FORK */
> 
> This change updates to provide `open-process' effectively on all systems
> instead of only if `fork' is available, but then it causes a runtime
> error if the system doesn't have `fork' and isn't `mingw32'.

Sorry, I don't follow: the change in fprintf fixes a simple type (the
function whose call failed is 'execvp', not 'execlp'.  Or are you
talking about something else?

> I guess that's OK in practice.  Would you mind updating the
> documentation in doc/ref/posix.texi to indicate this?  Thanks.

Once I understand the issue, sure.

Thanks.