From: Alex Vinokur <alexvn AT bigfoot DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: uclock() and struct rusage
Date: Tue, 27 Nov 2001 10:35:12 +0200
Organization: Scopus Network Technologies
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===============================================================
Windows98
gpp : GNU C++ version 2.95.3 20010315/djgpp (release) (djgpp)
      compiled by GNU C version 2.95.3 20010315/djgpp (release).
===============================================================

It seems that it is preferable to use uclock()
   instead of 'struct rusage' to get user time used by process
Resolution of uclock() is higher than 'struct rusage'.

UCLOCKS_PER_SEC is 1193180 // in time.h


See a test below.
Wee can we that sometimes 'struct rusage' returns 0 sec (when used time
is too small).


Nevertheless, is there any situations that
  it is worth using 'struct rusage' instead uclock()?

Answer#1. uclock() is non portable.

  Something else ?


//------------- C++ Code : BEGIN -------------

#include <iostream>
#include <sys/time.h>
#include <sys/resource.h>
#include <utime.h>


//-------------------------
uclock_t start_uclock_time;
uclock_t end_uclock_time;
struct rusage start_rusage_time;
struct rusage end_rusage_time;

//-------------------------
void set_start_time()
{
  start_uclock_time = uclock();
  getrusage(RUSAGE_SELF, &start_rusage_time);
}

//-------------------------
void set_end_time()
{
  end_uclock_time = uclock();
  getrusage(RUSAGE_SELF, &end_rusage_time);
}

//-------------------------
void show_user_used_time()
{
uclock_t used_uclock_time = end_uclock_time - start_uclock_time;
  cout << "User time used : "
 << used_uclock_time
 << " uclocks"
 << endl;

double user_rusage_time = (end_rusage_time.ru_utime.tv_sec -
start_rusage_time.ru_utime.tv_sec)
    + (end_rusage_time.ru_utime.tv_usec -
start_rusage_time.ru_utime.tv_usec)/ 1.0e6;

  cout << "User time used : "
 << user_rusage_time
 << " sec"
 << endl;

  cout << endl;
}

//------------
int main ()
{
#define TOTAL1 20
#define TOTAL2 1000000

  for (int i1 = 0; i1 < TOTAL1; i1++)
  {
    cout << "\t##### " << (i1 + 1) << " #####" << endl;
    set_start_time();
    for (int i2 = 0; i2 < TOTAL2; i2++)
    {
    }
    set_end_time();
    show_user_used_time();
  }

  return 0;
}

//-------------- C++ Code : END --------------


//-------------- Running : BEGIN -------------

%a.exe
 ##### 1 #####
User time used : 8709 uclocks
User time used : 0 sec

 ##### 2 #####
User time used : 8706 uclocks
User time used : 0 sec

 ##### 3 #####
User time used : 8706 uclocks
User time used : 0 sec

 ##### 4 #####
User time used : 8706 uclocks
User time used : 0 sec

 ##### 5 #####
User time used : 8706 uclocks
User time used : 0 sec

 ##### 6 #####
User time used : 8706 uclocks
User time used : 0 sec

 ##### 7 #####
User time used : 8706 uclocks
User time used : 0 sec

 ##### 8 #####
User time used : 41603 uclocks
User time used : 0.054945 sec

 ##### 9 #####
User time used : 8706 uclocks
User time used : 0 sec

 ##### 10 #####
User time used : 8706 uclocks
User time used : 0 sec

 ##### 11 #####
User time used : 8706 uclocks
User time used : 0 sec

 ##### 12 #####
User time used : 9955 uclocks
User time used : 0.054945 sec

 ##### 13 #####
User time used : 8707 uclocks
User time used : 0 sec

 ##### 14 #####
User time used : 8706 uclocks
User time used : 0 sec

 ##### 15 #####
User time used : 8706 uclocks
User time used : 0 sec

 ##### 16 #####
User time used : 8706 uclocks
User time used : 0 sec

 ##### 17 #####
User time used : 8706 uclocks
User time used : 0 sec

 ##### 18 #####
User time used : 8706 uclocks
User time used : 0 sec

 ##### 19 #####
User time used : 29672 uclocks
User time used : 0.054945 sec

 ##### 20 #####
User time used : 8706 uclocks
User time used : 0 sec


//--------------- Running : END --------------

  ===========================
  Alex Vinokur
    mailto:alexvn AT bigfoot DOT com
    mailto:alexvn AT dr DOT com
    http://up.to/alexvn
    http://go.to/alexv_math
  ===========================