Path: utzoo!attcan!uunet!know!zaphod.mps.ohio-state.edu!sdd.hp.com!hplabs!hpl-opus!hpnmdla!rajeev
From: rajeev@hpnmdla.HP.COM (Rajeev Menon)
Newsgroups: comp.unix.questions
Subject: Orphaned processes : Please explain
Message-ID: <2140001@hpnmdla.HP.COM>
Date: 14 Sep 90 22:03:30 GMT
Organization: HP Network Measurements Div, Santa Rosa, CA
Lines: 80

I am running HP-UX A.B3.10 on an HP 9000/855.

I am have a little program that creates three more processes, such that P0
the original process is parent of P1, which is parent of P2, etc. After
creating the processes, I ask each process to print out its PID and PPID
into a file called "junk". I am in no way synchronizing the processes, so
the order they write to this file is "random". But it doesn't seem random...
And sometimes it seems hard to explain. Can someone help ???

Here is the program called "fork.c"

--------------------------Cut here---------------------------------------
#include <stdio.h>
int cprocs(nprocs)
int nprocs;
{
  int i, pid;
  for ( i=0; i<nprocs; i++) {
      if ((pid = fork()) == -1)
         _exit(127);
      else if (pid)
         break;
  }
  return i;
}

main()
{
  int i, pid;
  FILE *fp; 
  if ( (fp = fopen("junk", "w")) == NULL )
     perror("Error in fopen");
  i = cprocs(3);
  fprintf( fp, "i=%d, pid = %d, ppid = %d.\n", i, getpid(), getppid());
  fclose(fp);
}
--------------------------Cut here---------------------------------------
Here is a sequence that I cannot understand :

% cc fork.c ; a.out ; cat junk
i=0, pid = 10593, ppid = 20487.
i=2, pid = 10598, ppid = 10597.
i=3, pid = 10599, ppid = 10598.
i=1, pid = 10597, ppid = 10593.
% cc fork.c ; a.out ; cat junk
i=0, pid = 10779, ppid = 20487.
i=2, pid = 10781, ppid = 10780.
% cc fork.c ; a.out ; cat junk
i=3, pid = 11122, ppid = 11121.
i=2, pid = 11121, ppid = 11120.
i=0, pid = 11119, ppid = 20487.
i=1, pid = 11120, ppid = 11119.

Sometimes (as in case 2),the file "junk" does not contain output from all 
the processes. Why ? Now I do

% a.out ; cat junk
i=0, pid = 11189, ppid = 20487.
i=1, pid = 11190, ppid = 1.
i=2, pid = 11191, ppid = 1.
i=3, pid = 11192, ppid = 1.
% a.out ; cat junk
i=2, pid = 11251, ppid = 11250.
i=3, pid = 11252, ppid = 1.
i=0, pid = 11249, ppid = 20487.
i=1, pid = 11250, ppid = 11249.

Some PPIDs show up as 1, showing that they have been orphaned, which could
be expected since I am not synchonizing the processes. But it really puzzles
me as to why this happens when I do "a.out ; cat junk" and not when I do 
"cc fork.c ; a.out ; cat junk". Can someone explain what is going on ?

Thanks

Rajeev Menon

Rajeev Menon				
Hewlett Packard Company			e-mail: rajeev@hpnmd.hp.com
1400 Fountaingrove Pkwy
Santa Rosa CA 95403