8.239 SYSTEM_CLOCK — Time function

Description:

Determines the COUNT of a processor clock since an unspecified time in the past modulo COUNT_MAX, COUNT_RATE determines the number of clock ticks per second. If the platform supports a high resolution monotonic clock, that clock is used and can provide up to nanosecond resolution. If a high resolution monotonic clock is not available, the implementation falls back to a potentially lower resolution realtime clock.

COUNT_RATE is system dependent and can vary depending on the kind of the arguments. For kind=4 arguments, COUNT usually represents milliseconds, while for kind=8 arguments, COUNT typically represents micro- or nanoseconds. COUNT_MAX usually equals HUGE(COUNT_MAX).

If there is no clock, COUNT is set to -HUGE(COUNT), and COUNT_RATE and COUNT_MAX are set to zero.

When running on a platform using the GNU C library (glibc), or a derivative thereof, the high resolution monotonic clock is available only when linking with the rt library. This can be done explicitly by adding the -lrt flag when linking the application, but is also done implicitly when using OpenMP.

Standard:

Fortran 95 and later

Class:

Subroutine

Syntax:

CALL SYSTEM_CLOCK([COUNT, COUNT_RATE, COUNT_MAX])

Arguments:

COUNT	(Optional) shall be a scalar of type INTEGER with INTENT(OUT).
COUNT_RATE	(Optional) shall be a scalar of type INTEGER with INTENT(OUT).
COUNT_MAX	(Optional) shall be a scalar of type INTEGER with INTENT(OUT).

Example:

          PROGRAM test_system_clock
            INTEGER :: count, count_rate, count_max
            CALL SYSTEM_CLOCK(count, count_rate, count_max)
            WRITE(*,*) count, count_rate, count_max
          END PROGRAM

See also:

DATE_AND_TIME, CPU_TIME