Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!uwm.edu!uwvax!astroatc!nicmad!madnix!henning
From: henning@madnix.UUCP (Mark D. Henning)
Newsgroups: comp.sys.amiga.programmer
Subject: child process I/O problem (source included)
Keywords: help, I/O, child, parent
Message-ID: <1792@madnix.UUCP>
Date: 3 Apr 91 04:40:32 GMT
Organization: MADNIX, operated by: ARP Software  Madison WI
Lines: 135


Hello.  
   I have a rather complicated programming problem.  I am not sure
where it lies, but it is rather nasty.  

What I am trying to accomplish is to have a syncronous process place
data into a temproary file, eventually receiving its input from a
temporary file created by the parent process.

I had originally tried to do this using the pipe device as the output
stream of the child process, but I ran into a problem of the parent
blocking forever, waiting for an end of file so that it's final read
could be processed.  This made me decide to use temp files.  I use the 
Aztec fexecv function so that the parent waits till' the child is
finished. (I used the AmigaDos Execute when working with the pipe
device, as it would block anyway if its buffer overran, thus allowing
the parent to slurp the output as the child delivered it.)

The redefining of pr_COS worked fine without the redefining of pr_CIS.
Therefore I am not forgetting any BCPL garbage (I think?)  However,
when I debug through the parent program, somewhere during the fexecv
memory location 0000000 is written 0a000000.  Future calls can cause a guru.

The filter works with the equivelent function in a shell:

filter <foo >tmp

Therefore Either I am forgetting to set something in my process
structure to reflect the new CIS, or fexecv does something fishy.

Please help.  This is the final routine to make GNU emacs a full port.
Once this is accomplished, I can start to revamp the interface, making
it more ``intuition'' friendly, and get to fixing the elusive file
completion across devices bug.

Thanks in advance,

				Mark Henning

P.S. C code for examples follows the signature.

--------------------------------------------------------------------------
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--------------------------------------------------------------------------

/************************************************
 * useless filter, but good for testing purposes
 ************************************************/

#include <stdio.h>
main ()
{
 char c;
while ((c = getchar()) != EOF){
 putchar(c);
 putchar(c);
}
exit (0);
}


/***************************************************************************
 * second program, the parent.
 *****************************************************************/



#include <functions.h>
#include <exec/tasks.h>
#include <libraries/dosextens.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
  

int child_setup(new_argv, nametem)
  register char **new_argv;
  char *nametem;
{
  struct FileHandle *sout,*sin;
  struct Process *SyncProc;
  int fd,ok;  
  
  SyncProc = (struct Process *)FindTask (0);
  sout = SyncProc->pr_COS;
  sin = SyncProc->pr_CIS;
  SyncProc->pr_COS = Open (nametem, MODE_NEWFILE);
  SyncProc->pr_CIS = Open ("wrk:syncprocess/foo", MODE_OLDFILE); 
  ok = fexecv (new_argv[0], new_argv);
  Close (SyncProc->pr_COS);
  Close (SyncProc->pr_CIS);
  SyncProc->pr_COS = sout;
  SyncProc->pr_CIS = sin;
  return ok;
}


void main ()
{
  int fd;
  int nread;
  char buf[80];
  char *args[2] =
    {
      "filter",
      (char *) 0
      };
  char *name;  
  
  name = mktemp ("t:emacspipeXXXX");

  if (child_setup(args, name) == -1)
    {
       fprintf(stderr,"error in child process #%d\n",errno);
       exit(-1);
    }
  fd = open (name , O_RDONLY );
  while ((nread = read (fd, buf, sizeof buf)) >0)
    {
      write (fileno(stdout), buf, nread );
    }
  close (fd);
}



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