NAME

       times - get process and waited-for child process times

SYNOPSIS

       #include <sys/times.h>

       clock_t times(struct tms *buffer);

DESCRIPTION

       The  times() function shall fill the tms structure pointed to by buffer with time-accounting information.
       The tms structure is defined in <sys/times.h>.

       All times are measured in terms of the number of clock ticks used.

       The times of a terminated child process shall be included in the tms_cutime and  tms_cstime  elements  of
       the  parent  when wait() or waitpid() returns the process ID of this terminated child. If a child process
       has not waited for its children, their times shall not be included in its times.

        * The tms_utime structure member is the CPU time charged for the execution of user instructions  of  the
          calling process.

        * The  tms_stime  structure  member is the CPU time charged for execution by the system on behalf of the
          calling process.

        * The tms_cutime structure member is the sum  of  the  tms_utime  and  tms_cutime  times  of  the  child
          processes.

        * The  tms_cstime  structure  member  is  the  sum  of  the  tms_stime and tms_cstime times of the child
          processes.

RETURN VALUE

       Upon successful completion, times() shall return  the  elapsed  real  time,  in  clock  ticks,  since  an
       arbitrary  point  in  the  past  (for example, system start-up time). This point does not change from one
       invocation of times() within the process to another. The return value may overflow the possible range  of
       type clock_t. If times() fails, (clock_t)-1 shall be returned and errno set to indicate the error.

ERRORS

       No errors are defined.

       The following sections are informative.

EXAMPLES

   Timing a Database Lookup
       The  following  example  defines  two  functions,  start_clock() and end_clock(), that are used to time a
       lookup. It also defines variables of type clock_t and tms to measure the duration  of  transactions.  The
       start_clock() function saves the beginning times given by the times() function.  The end_clock() function
       gets the ending times and prints the difference between the two times.

              #include <sys/times.h>
              #include <stdio.h>
              ...
              void start_clock(void);
              void end_clock(char *msg);
              ...
              static clock_t st_time;
              static clock_t en_time;
              static struct tms st_cpu;
              static struct tms en_cpu;
              ...
              void
              start_clock()
              {
                  st_time = times(&st_cpu);
              }

              /* This example assumes that the result of each subtraction
                 is within the range of values that can be represented in
                 an integer type. */
              void
              end_clock(char *msg)
              {
                  en_time = times(&en_cpu);

                  fputs(msg,stdout);
                  printf("Real Time: %jd, User Time %jd, System Time %jd\n",
                      (intmax_t)(en_time - st_time),
                      (intmax_t)(en_cpu.tms_utime - st_cpu.tms_utime),
                      (intmax_t)(en_cpu.tms_stime - st_cpu.tms_stime));
              }

APPLICATION USAGE

       Applications  should use sysconf(_SC_CLK_TCK) to determine the number of clock ticks per second as it may
       vary from system to system.

RATIONALE

       The accuracy of the times reported is intentionally left unspecified to allow implementations flexibility
       in design, from uniprocessor to multi-processor networks.

       The inclusion of times of child processes is recursive, so that a parent process may  collect  the  total
       times  of all of its descendants. But the times of a child are only added to those of its parent when its
       parent successfully waits on the child. Thus, it is not guaranteed that a parent process can  always  see
       the total times of all its descendants; see also the discussion of the term ``realtime'' in alarm() .

       If  the  type clock_t is defined to be a signed 32-bit integer, it overflows in somewhat more than a year
       if there are 60 clock ticks per second, or less than a year  if  there  are  100.  There  are  individual
       systems  that  run  continuously  for  longer  than  that. This volume of IEEE Std 1003.1-2001 permits an
       implementation to make the reference point for the returned value be the start-up time  of  the  process,
       rather than system start-up time.

       The  term  ``charge''  in  this context has nothing to do with billing for services. The operating system
       accounts for time used in this way. That information must be correct, regardless of how that  information
       is used.

FUTURE DIRECTIONS

       None.

SEE ALSO

       alarm()   ,  exec()  ,  fork()  ,  sysconf()  ,  time()  ,  wait()  ,  the  Base  Definitions  volume  of
       IEEE Std 1003.1-2001, <sys/times.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
       Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open  Group  Base
       Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,
       Inc  and  The  Open Group. In the event of any discrepancy between this version and the original IEEE and
       The Open Group Standard, the original IEEE and The Open Group  Standard  is  the  referee  document.  The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group                                   2003                                              TIMES(P)