huschi.net

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 (consult 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  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 wait-
       pid() 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  exe-
          cution 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, sys-
       tem 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 par-
       ent 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  over-
       flows in somewhat more than a year if there are 60 clock ticks per sec-
       ond, 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 Defini-
       tions 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(3P)