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wall clock time

 
 
aegis
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      12-15-2004
What is wall clock time? the standard doesn't define it
but I see its use in past posts on clc.



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aegis

 
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Lew Pitcher
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      12-15-2004
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aegis wrote:
> What is wall clock time? the standard doesn't define it
> but I see its use in past posts on clc.


The term "Wall clock time" refers to the elapsed time that an activity
takes, and alludes to the method of timing such an activity: look at the
wall clock when the activity starts, look again when the activity ends,
compute the difference between the two times.

We use this term in contrast to "cpu time", which measures the elapsed
time that an activity takes, excluding all the time the computer is not
performing tasks for that activity (i.e. "data entry" time, etc.).

- --

Lew Pitcher, IT Consultant, Enterprise Data Systems
Enterprise Technology Solutions, TD Bank Financial Group

(Opinions expressed here are my own, not my employer's)
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Zoran Cutura
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      12-15-2004
aegis <(E-Mail Removed)> wrote:
> What is wall clock time? the standard doesn't define it
> but I see its use in past posts on clc.


Well its the time that your clock on the wall shows.
There need not be any tool, function or else that provides
your C programs with this information, system specific extensions make
make this available.

--
Z ((E-Mail Removed))
"LISP is worth learning for the profound enlightenment experience
you will have when you finally get it; that experience will make you
a better programmer for the rest of your days." -- Eric S. Raymond
 
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Mike Wahler
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      12-15-2004
"aegis" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ups.com...
> What is wall clock time?


I don't know of any standardized meaning for it, but
I'd guess it means 'local time'.

> the standard doesn't define it


Nope.

> but I see its use in past posts on clc.


Perhaps if you give context, we could figure out
what the poster(s) meant.

-Mike


 
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Gordon Burditt
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      12-15-2004
>What is wall clock time? the standard doesn't define it
>but I see its use in past posts on clc.


The time according to a clock on a nearby wall, presuming it is
properly set. This clock would be set according to the local time
zone, and local daylight savings time conventions (if any). WHOSE
wall may be an issue if the user and the system are in different
time zones. A wall clock runs continuously, as distinguished from
a stopwatch.

A Football Game Clock runs only when plays are actually in progress,
and not during timeouts and between plays. A CPU time clock runs
only when the program is using the CPU. When a program is "using
the CPU" is a bit system-specific, but on a multi-tasking system
this generally does not include times the program is waiting for
input, is waiting for disk I/O, paging, or swapping, or is not
scheduled due to other programs running.

Gordon L. Burditt
 
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Merrill & Michele
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      12-15-2004

"aegis"
> What is wall clock time? the standard doesn't define it
> but I see its use in past posts on clc.


At the risk of making the same error twice in a day, I think wall clock time
is OT as only the difference in time can be handled by C. Otherwise you're
making a system call. If you stipulate any particular t1 then wall clock
time is within the scope of ISO C. MPJ


 
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Goran Larsson
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      12-15-2004
In article <(E-Mail Removed)>,
Merrill & Michele <(E-Mail Removed)> wrote:

> At the risk of making the same error twice in a day, I think wall clock time
> is OT as only the difference in time can be handled by C.


What about the standard C function time()?

> Otherwise you're
> making a system call.


Why is a "system call" used by time() different than a "system call"
used by printf()? A standard C function may, or may not, do one or
more "system calls" but that is up to the implementation, i.e. it is
outside of the standard.

--
Göran Larsson http://www.mitt-eget.com/
 
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Keith Thompson
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      12-15-2004
Zoran Cutura <(E-Mail Removed)> writes:
> aegis <(E-Mail Removed)> wrote:
>> What is wall clock time? the standard doesn't define it
>> but I see its use in past posts on clc.

>
> Well its the time that your clock on the wall shows.
> There need not be any tool, function or else that provides
> your C programs with this information, system specific extensions make
> make this available.


See <time.h>. The time() function gives you a representation of what
I'd refer to as "wall clock time" (as distinct from CPU time).

I suppose "wall clock time" could refer either to a given moment or to
an elapsed time; the latter can be computed by calling difftime().

No system specific extensions are necessary, unless you need some
particular resolution -- or unless you're using the phrase "wall clock
time" to refer to something other than what I'm thinking of.

--
Keith Thompson (The_Other_Keith) http://www.velocityreviews.com/forums/(E-Mail Removed) <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.
 
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Lawrence Kirby
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      12-16-2004
On Wed, 15 Dec 2004 13:16:20 -0600, Merrill & Michele wrote:

>
> "aegis"
>> What is wall clock time? the standard doesn't define it
>> but I see its use in past posts on clc.

>
> At the risk of making the same error twice in a day, I think wall clock time
> is OT as only the difference in time can be handled by C. Otherwise you're
> making a system call. If you stipulate any particular t1 then wall clock
> time is within the scope of ISO C. MPJ



Wall clock time usually refers to time intervals. E.g. a program was
running for 10 seconds and used 4 seconds of CPU time. The 10 seconds
there is wall clock time, the 4 seconds isn't.

Lawrence



 
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Merrill & Michele
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      12-16-2004

> "Lawrence Kirby"
> > Merrill & Michele wrote:

>
> >
> > "aegis"
> >> What is wall clock time? the standard doesn't define it
> >> but I see its use in past posts on clc.

> >
> > At the risk of making the same error twice in a day, I think wall clock

time
> > is OT as only the difference in time can be handled by C. Otherwise

you're
> > making a system call. If you stipulate any particular t1 then wall

clock
> > time is within the scope of ISO C. MPJ

>
>
> Wall clock time usually refers to time intervals. E.g. a program was
> running for 10 seconds and used 4 seconds of CPU time. The 10 seconds
> there is wall clock time, the 4 seconds isn't.


What chapter is that in C Unleashed (you guys didn't do the greatest job of
indexing. You did the bitshift stuff and I think a couple more, but the
only way for me to really find anything in that book is sit down and slog
through 400 pages. Maybe a cleaner presentation in version 2?)? MPJ


 
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