C-c in guile

C-c in guile

[Alex Vong]

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Hello,

When running the external program "yes" in shell,

  $ yes

We can terminate the process by pressing C-c.

However, when running the external program "yes" in guile,

  $ guile -c '(system* "yes")'

We cannot terminate the process by pressing C-c,
but we can suspend it by pressing C-z.

Why is that? Is there any way I can terminate the process by pressing
C-c?

Thanks,
Alex

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Re: C-c in guile

[Matt Wette]

> On Jan 21, 2017, at 3:55 AM, Alex Vong <alexvong1995@gmail.com> wrote:
> 
> Hello,
> 
> When running the external program "yes" in shell,
> 
>  $ yes
> 
> We can terminate the process by pressing C-c.
> 
> However, when running the external program "yes" in guile,
> 
>  $ guile -c '(system* "yes")'
> 
> We cannot terminate the process by pressing C-c,
> but we can suspend it by pressing C-z.
> 
> Why is that? Is there any way I can terminate the process by pressing
> C-c?
> 
> Thanks,
> Alex

C-c works on your guile example for me on my Mac.  Try `C-\’.

Re: C-c in guile

[Alex Vong]

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Matt Wette <matt.wette@gmail.com> writes:

>> On Jan 21, 2017, at 3:55 AM, Alex Vong <alexvong1995@gmail.com> wrote:
>> 
>> Hello,
>> 
>> When running the external program "yes" in shell,
>> 
>>  $ yes
>> 
>> We can terminate the process by pressing C-c.
>> 
>> However, when running the external program "yes" in guile,
>> 
>>  $ guile -c '(system* "yes")'
>> 
>> We cannot terminate the process by pressing C-c,
>> but we can suspend it by pressing C-z.
>> 
>> Why is that? Is there any way I can terminate the process by pressing
>> C-c?
>> 
>> Thanks,
>> Alex
>
> C-c works on your guile example for me on my Mac.  Try `C-\’.

Hmmm... Neither does 'C-\' work on the guile example. It works on the
shell example though.

I am running Debian with 'uname -a' being:
  Linux debian 4.8.0-2-amd64 #1 SMP Debian 4.8.15-2 (2017-01-04) x86_64 GNU/Linux

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Re: C-c in guile

[Vladimir Zhbanov]

On Sun, Jan 22, 2017 at 02:54:31PM +0800, Alex Vong wrote:
> Matt Wette <matt.wette@gmail.com> writes:
> 
> >> On Jan 21, 2017, at 3:55 AM, Alex Vong <alexvong1995@gmail.com> wrote:
> >> 
> >> Hello,
> >> 
> >> When running the external program "yes" in shell,
> >> 
> >>  $ yes
> >> 
> >> We can terminate the process by pressing C-c.
> >> 
> >> However, when running the external program "yes" in guile,
> >> 
> >>  $ guile -c '(system* "yes")'
> >> 
> >> We cannot terminate the process by pressing C-c,
> >> but we can suspend it by pressing C-z.
> >> 
> >> Why is that? Is there any way I can terminate the process by pressing
> >> C-c?
> >> 
> >> Thanks,
> >> Alex
> >
> > C-c works on your guile example for me on my Mac.  Try `C-\’.
> 
> Hmmm... Neither does 'C-\' work on the guile example. It works on the
> shell example though.
> 
> I am running Debian with 'uname -a' being:
>   Linux debian 4.8.0-2-amd64 #1 SMP Debian 4.8.15-2 (2017-01-04) x86_64 GNU/Linux

I see the same having a bit older debian and guile 2.0.11. Some
experiments have shown that in such a case `guile' and `yes' do
not react to SIGINT (which IIUC C-c produces) while handle SIGTERM
correctly.

-- 
  Vladimir

Re: C-c in guile

[Andy Wingo]

On Sat 21 Jan 2017 12:55, Alex Vong <alexvong1995@gmail.com> writes:

> However, when running the external program "yes" in guile,
>
>   $ guile -c '(system* "yes")'
>
> We cannot terminate the process by pressing C-c,

Indeed I can reproduce this!

> but we can suspend it by pressing C-z.

I believe the C-z is handled by the shell, not Guile; AFAIU.

I don't know how this should work (mechanics) but I agree with you that
probably it should!

Andy

Re: C-c in guile

[Alex Vong]

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Andy Wingo <wingo@pobox.com> writes:

> On Sat 21 Jan 2017 12:55, Alex Vong <alexvong1995@gmail.com> writes:
>
>> However, when running the external program "yes" in guile,
>>
>>   $ guile -c '(system* "yes")'
>>
>> We cannot terminate the process by pressing C-c,
>
> Indeed I can reproduce this!
>
>> but we can suspend it by pressing C-z.
>
> I believe the C-z is handled by the shell, not Guile; AFAIU.
>
> I don't know how this should work (mechanics) but I agree with you that
> probably it should!
>
I've just checked, a python equivalence of the above command works:

     $ python -c 'import subprocess; subprocess.call("yes")'

Maybe some ideas can be extracted from it.

> Andy

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Re: C-c in guile

[Alex Vong]

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Hello,


I manage to find a solution: define a new procedure 'system**' which is
implemented in C using fork-exec-waitpid. The code is in the attchment.


To compile the C extension, run:

  $ gcc -o libguile-system_star_star.so -shared -fPIC \
  `pkg-config --cflags guile-2.2` -O2 -Wall -Wextra system_star_star.c


To test the C extension, try running something like:

  (use-modules (ice-9 threads))
  (load-extension "./libguile-system_star_star" "init_system_star_star")

  (define n 10000)
  (define s (make-string n #\s))
  (define l (make-list n s))

  (define main
    (lambda _
      (parallel (system** "echo" "foo" "bar")
                (apply system** l)
                (system** "echo" "foo" "bar")
                (apply system** l))))


C-c should terminate the program.


My first solution was to use 'primitive-fork'. But it didn't work,
because guile warned me that 'primitive-fork' shouldn't be called in a
multithreaded program. I want to find out why. So I read the man-page
and it says after forking in a multithread program, it is only safe to
call async-safe functions. So I re-implement the whole thing in C and
exec right after forking. This is how I come up with the current
solution.



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/* Copyright (C) 2017 Alex Vong <alexvong1995@gmail.com>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public License
 * as published by the Free Software Foundation; either version 3 of
 * the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301 USA
 */

#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <libguile.h>

static SCM
system_star_star(SCM prog, SCM args)
{
  SCM prog_args = scm_cons(prog, args);
  size_t len = scm_to_size_t(scm_length(prog_args));
  char **argv = scm_gc_malloc((len + 1) * sizeof(char *), "argv");

  for (size_t k = 0; k < len; ++k)
    {
      SCM arg = SCM_CAR(prog_args);
      size_t len = scm_c_string_length(arg);

      argv[k] = scm_gc_malloc_pointerless(len + 1, "argv[k]");
      scm_to_locale_stringbuf(arg, argv[k], len);
      argv[k][len] = '\0';

      prog_args = SCM_CDR(prog_args);
    }
  argv[len] = NULL;

  int status = 0;
  pid_t pid = fork();
  if (pid == -1)
    scm_syserror("system**");

  if (pid == 0) /* child  */
    {
      execvp(argv[0], argv);
      _exit(127);
    }
  else /* parent  */
    {
      if (waitpid(pid, &status, 0) == -1)
        scm_syserror("system**");
    }

  return scm_from_int(status);
}

void
init_system_star_star(void)
{
  scm_c_define_gsubr("system**", 1, 0, 1, system_star_star);
}

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Cheers,
Alex


Alex Vong <alexvong1995@gmail.com> writes:

> Hello,
>
> When running the external program "yes" in shell,
>
>   $ yes
>
> We can terminate the process by pressing C-c.
>
> However, when running the external program "yes" in guile,
>
>   $ guile -c '(system* "yes")'
>
> We cannot terminate the process by pressing C-c,
> but we can suspend it by pressing C-z.
>
> Why is that? Is there any way I can terminate the process by pressing
> C-c?
>
> Thanks,
> Alex

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