9.92 DTIME — Execution time subroutine (or function)

Description:

DTIME(VALUES, TIME) initially returns the number of seconds of runtime since the start of the process’s execution in TIME. VALUES returns the user and system components of this time in VALUES(1) and VALUES(2) respectively. TIME is equal to VALUES(1) + VALUES(2).

Subsequent invocations of DTIME return values accumulated since the previous invocation.

On some systems, the underlying timings are represented using types with sufficiently small limits that overflows (wrap around) are possible, such as 32-bit types. Therefore, the values returned by this intrinsic might be, or become, negative, or numerically less than previous values, during a single run of the compiled program.

Please note, that this implementation is thread safe if used within OpenMP directives, i.e., its state will be consistent while called from multiple threads. However, if DTIME is called from multiple threads, the result is still the time since the last invocation. This may not give the intended results. If possible, use CPU_TIME instead.

This intrinsic is provided in both subroutine and function forms; however, only one form can be used in any given program unit.

VALUES and TIME are INTENT(OUT) and provide the following:

	VALUES(1):	User time in seconds.
	VALUES(2):	System time in seconds.
	TIME:	Run time since start in seconds.

Standard:

GNU extension

Class:

Subroutine, function

Syntax:

CALL DTIME(VALUES, TIME).

TIME = DTIME(VALUES), (not recommended).

Arguments:

VALUES	The type shall be REAL(4), DIMENSION(2).
TIME	The type shall be REAL(4).

Return value:

Elapsed time in seconds since the last invocation or since the start of program execution if not called before.

Example:

program test_dtime
    integer(8) :: i, j
    real, dimension(2) :: tarray
    real :: result
    call dtime(tarray, result)
    print *, result
    print *, tarray(1)
    print *, tarray(2)   
    do i=1,100000000    ! Just a delay
        j = i * i - i
    end do
    call dtime(tarray, result)
    print *, result
    print *, tarray(1)
    print *, tarray(2)
end program test_dtime

See also:

CPU_TIME

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