Unix/Linux Go Back    


Linux 2.6 - man page for times (linux section 3posix)

Linux & Unix Commands - Search Man Pages
Man Page or Keyword Search:   man
Select Man Page Set:       apropos Keyword Search (sections above)


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

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-account-
       ing 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  dura-
       tion  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  differ-
       ence 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  implementa-
       tions flexibility in design, from uniprocessor to multi-processor networks.

       The  inclusion of times of child processes is recursive, so that a parent process may col-
       lect 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 guar-
       anteed 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 oper-
       ating system accounts for time used in this way. That information must be correct, regard-
       less 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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					 TIMES(P)
Unix & Linux Commands & Man Pages : ©2000 - 2018 Unix and Linux Forums


All times are GMT -4. The time now is 08:13 AM.