Subj : Re: usage of time() for timeout handling
To   : comp.arch.embedded,comp.programming
From : Willem
Date : Wed Jul 27 2005 10:49 pm

David wrote:
) Hi gurus,
) I'm having some modules, that use time() for determine if a given activity
) has timed out. As the operating system time will be updated periodically
) with the time or the RTC chip, it is possible that the result of two calls

A good operating system will not 'jump' the OS clock to the correct
time, it will slow down or speed up the OS clock so that it will match
the correct timeafter a while.  (Unless the jump is too great, in which
case it will do it at once, but with a warning in a log file of some sort.)

) to time() would give a smaller value on the second call. This would cause
) the timeout calculation to fail and result in unexpected behaviour.
) This situation could specially occour if the user changed the time of the
) system! How are you handling this problem? On could use the system tick for
) timeout calculations. But somewhere I read that for acuracy reason you
) should not do this for longer timeouts. How do you handle this problem?

There are usually system calls that return different clocks that do not
suffer from this problem, because they aren't synchronized with world time.


SaSW, Willem
-- 
Disclaimer: I am in no way responsible for any of the statements
            made in the above text. For all I know I might be
            drugged or something..
            No I'm not paranoid. You all think I'm paranoid, don't you !
#EOT

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