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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(), waitid(),
       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 exe‐
	   cution of user instructions of the calling process.

	*  The	tms_stime  structure member is the CPU time charged for execu‐
	   tion 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 POSIX.1‐2008
       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(), waitid()

       The Base Definitions volume of POSIX.1‐2008, <sys_times.h>

COPYRIGHT
       Portions	 of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       --  Portable  Operating	System	Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
       cal  and	 Electronics  Engineers,  Inc  and  The	 Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum	 1  applied.)  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.unix.org/online.html .

       Any typographical or formatting errors that appear  in  this  page  are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors,	 see  https://www.ker‐
       nel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group		     2013			     TIMES(3P)
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