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Date: Mon, 17 Jan 2000 15:41:34 +0100 (MET)
From: Ariel Burbaickij <Ariel.Burbaickij@mni.fh-giessen.de>
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To: freebsd-questions@freebsd.org
Subject: understanding timing
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We got homework to implement shell.I am ready so far .So this mail is not
begging for doing my work by anyone else :)).We got some solution pattern
from out teacher suggesting following:

void do_with_time(int argc,char * argv [])//function for doing it.
{
clock_t start ,end ;
struct tm tnt ;
pid_t pid1 ,pid2 //YTou already see here it is about using two forks.

if(argc > 1)//we expect the coomand proper as well

{
  pid1 = fork()
  switch(pid1)
  {
   case -1 :
   /* fear ,fire ,foes */
   case 0 :
   {  
      start = times(&tnt);
      pid2  = fork()
      switch(pid2)
      {
        case -1 :
        /* fear fire ,foes */
        case 0 :
        {
        execvp(argv[1],&argv[1]);
        printf("You should never see me!");
        }
        default:
        waitpid(pid,NULL,NULL) //quick and dirty
        end = times(&tnt);
        /* kind 
        printf(Real time is difference between end and start);
        printf(System time is &time.tms_cstime);//evaluation order is
        //surely against us
    }//end of second switch
   default :
   waitpid(pid,NULL,NULL);
  }//end of first switch
}//end of if
else
printf(You need at least two to dance tango);
What i do not understand is why you need two fork's() already provided
with waitpid()and so having mechanism for waiting for well-defined
child,so eliminating the danger of cumulating the childrens' time
in tms structrue.I would understand with wait() only.But here I guess
I need a little help from you.

kind regards,
Ariel

        
   
        



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