SECOND(3F) Last changed: 2-24-98
NAMESECOND - Returns elapsed CPU time
SYNOPSIS
All systems:
second=SECOND()
UNICOS systems:
CALL SECOND(second)IMPLEMENTATION
UNICOS, UNICOS/mk and IRIX systems
DESCRIPTIONSECOND returns the elapsed user CPU time as a real number in seconds
(a default REAL*4) since the start of a program, including time
accumulated by all processes in a multitasking program.
SECOND returns execution time only for the current program. For
example, a script runs a 50-second program 10 times. A SECOND call at
the end of the 10th run (or 1st or 3rd or 7th) returns 50 seconds.
On UNICOS systems, SECOND is not appropriate for timing small timed
regions. If the timed region is fewer than 4000 clock periods (CPs)
in duration, the variation in the accuracy of SECOND can be 10% or
more on one processor. On multiple processors, the variation can be
on the order of 10,000 to 400,000 CPs.
The second argument is the result, or CPU time (in type real seconds)
accumulated by all processes in a program.
NOTES
On UNICOS systems, the initial call to SECOND may take longer than
subsequent calls due to certain initializations performed by the
routine. If the cost of calling SECOND is important, ignore the
initial call when computing SECOND's time. The calculation of
OVERHEAD in the second example, following, serves this purpose. On
UNICOS systems, the CPU times gathered by SECOND include
wait-semaphore time.
WARNINGS
If you are trying to time your entire program, and you are using
Autotasking, the CPU time returned by SECOND may not reflect all of
the CPU time used by your program. This is due to the fact that slave
CPUs may be still active when your program terminates (for instance,
with a STOP or END statement). Depending on the number of active CPUs
on your machine, the extra time needed to terminate the slaves may be
substantial compared with your program time. Thus, if you use SECOND
to time your program, and you are also using time(1) or ja(1), the
time reported by these other utilities could be much higher than that
reported by SECOND.
Because of the large variation on multiple processors, SECOND should
be used cautiously in multitasked routines. On IRIX systems, the
presence of multitasking does not affect the accuracy of SECOND.
EXAMPLES
Example 1: This example calculates the CPU time used in DOWORK:
BEFORE = SECOND( )
CALL DOWORK( )
AFTER = SECOND( )
CPUTIME = AFTER - BEFORE
Example 2: If the CPU time is small enough that the overhead for
calling SECOND may be significant, the following example is more
accurate:
T0 = SECOND( )
OVERHEAD = SECOND( ) - T0
BEFORE = SECOND( )
CALL DOWORK( )
AFTER = SECOND( )
CPUTIME = (AFTER - BEFORE) - OVERHEAD
SEE ALSORTC(3I), SECONDR(3F), TIMEF(3F), TSECND(3F)ja(1), time(1) in the UNICOS User Commands Reference Manual,
publication SR-2011
Application Programmer's Library Reference Manual, publication
SR-2165, for the printed version of this man page.
