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 .