TIMES(3P)                                           POSIX Programmer's Manual                                          TIMES(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

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 struc-
       ture 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,  Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                     TIMES(3P)