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

       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.

       times - get process and waited-for child process times

       #include <sys/times.h>

       clock_t times(struct tms *buffer);

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

       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.

       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.

       No errors are defined.

       The following sections are informative.

   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;
		  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. */
	      end_clock(char *msg)
		  en_time = times(&en_cpu);

		  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));

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

       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


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

       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)

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