Re: [Gcl-devel] read-char-no-hang

[Camm Maguire]

Greetings!

OK, my thought is that it is rather kernel related, and there is
something wrong/changed about the FIONREAD ioctl on standard terminal
file pointers.

To test:

echo '#undef LISTEN_FOR_INPUT' >>h/config.h
make h/cmpinclude.h
cd o
touch file.d
cd ..
rm unixport/saved_ansi_gcl
make

(Make sure file.o is remade).

Here is the 'fast' listen code implemented in linux.h for this
platform:

#undef LISTEN_FOR_INPUT
#define LISTEN_FOR_INPUT(fp) \
do { int c = 0; \
  if(((fp)->_IO_read_ptr >= (fp)->_IO_read_end) \
     && (ioctl((fp)->_fileno, FIONREAD, &c),c<=0)) \
     return 0;} while (0)


Here is the default fallback when the analog of the above is
unavailable (file.d):

#ifdef LISTEN_USE_FCNTL
  do { int c = 0;
  FILE *fp = strm->sm.sm_fp;
  int orig;
  int res;
  if (feof(fp)) return TRUE;
  orig = fcntl(fileno(fp), F_GETFL);
  if (! (orig & O_NONBLOCK ) ) {
    res=fcntl(fileno(fp),F_SETFL,orig | O_NONBLOCK);
  }
  c = getc(fp);
  if (! (orig & O_NONBLOCK ) ){
    fcntl(fileno(fp),F_SETFL,orig );
  }
  if (c != EOF)
    { 
      ungetc(c,fp);
      return TRUE;
    }
  return FALSE;
  } while (0);
#endif

LISTEN_USE_FCNTL must be set by configure, which is basically always
the case as far as I can tell.

It would be helpful if someone could point to where to read up on the
FIONREAD iocntl on newer machines.  I suppose the linux kernel doc is
as good a place as any, but these items have always been poorly
documented. 

Take care,


James Amundson <address@hidden> writes:

> On Mon, 2005-02-14 at 10:04, Camm Maguire wrote:
> > Greetings!
> 
> Thanks for looking into this.
> 
> > I can't reproduce this, but rather get:
> 
> On my system, read-char-no-hang and listen always return nil. I attached
> my output from foo and foo2 to the end of this message. I'm afraid it
> must be a gcc and/or libc issue. Here are my versions:
> 
> |abacus3>gcc --version
> gcc (GCC) 3.2.3 20030502 (Red Hat Linux 3.2.3-42)
> Copyright (C) 2002 Free Software Foundation, Inc.
> This is free software; see the source for copying conditions.  There is
> NO
> warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
> PURPOSE.
> 
> |abacus3>/lib/libc.so.6 --version
> GNU C Library stable release version 2.3.2, by Roland McGrath et al.
> Copyright (C) 2003 Free Software Foundation, Inc.
> This is free software; see the source for copying conditions.
> There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
> PARTICULAR PURPOSE.
> Compiled by GNU CC version 3.2.3 20030502 (Red Hat Linux 3.2.3-42).
> Compiled on a Linux 2.4.20 system on 2004-12-20.
> Available extensions:
>         GNU libio by Per Bothner
>         crypt add-on version 2.1 by Michael Glad and others
>         linuxthreads-0.10 by Xavier Leroy
>         The C stubs add-on version 2.1.2.
>         BIND-8.2.3-T5B
>         NIS(YP)/NIS+ NSS modules 0.19 by Thorsten Kukuk
>         Glibc-2.0 compatibility add-on by Cristian Gafton
>         libthread_db work sponsored by Alpha Processor Inc
> Thread-local storage support included.
> For bug reporting instructions, please see:
> <http://www.gnu.org/software/libc/bugs.html>.
> 
> I'm not sure what debugging steps to try next. I tried to understand how
> read-char-no-hang and listen are implemented in the gcl source, but I
> couldn't see it. Any pointers?      
> 
> Thanks,
> Jim
> 
> P.S.
> 
> GCL (GNU Common Lisp)  2.6.6 ANSI    Feb 14 2005 21:03:12
> Source License: LGPL(gcl,gmp), GPL(unexec,bfd)
> Binary License:  GPL due to GPL'ed components: (READLINE BFD UNEXEC)
> Modifications of this banner must retain notice of a compatible license
> Dedicated to the memory of W. Schelter
> 
> Use (help) to get some basic information on how to use GCL.
> 
> >(defun foo ()
>   (format t "normal: '~a'~%" (read-char))
>   (format t "normal: '~a'~%" (read-char))
>   (format t "no-hang: '~a'~%" (read-char-no-hang))
>   (format t "normal: '~a'~%" (read-char))
>   (read-line))
> 
> FOO
> 
> >(foo)
> normal: '
> '
> abcde
> normal: 'a'
> no-hang: 'NIL'
> normal: 'b'
> "cde"
> NIL
> 
> >(defun foo2 ()
>   (do ()
>       ((not (listen)))
>     (read-char-no-hang))
>   (foo))
> 
> FOO2
> 
> >(foo2)
> normal: '
> '
> abcdef
> normal: 'a'
> no-hang: 'NIL'
> normal: 'b'
> "cdef"
> NIL
> 
> >
> 
> 
> 
> 
> 

-- 
Camm Maguire                                            address@hidden
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