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



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

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
           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
       The times() function shall fail if:

       EOVERFLOW
              The return value would overflow the range of clock_t.

       The following sections are informative.

EXAMPLES
   Timing aa 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
       POSIX.1-2017 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.1-2017, <sys_times.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       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.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                             TIMES(3)
