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Re: [patch,fortran] Fix corner case where consecutive calls to date_and_time can return times out of sequence (PR30015)


Paul Thomas wrote:
Tobias,
The change by Mat Cross is therefore:
- Moving the gettimeofday() block up in the file
- Using the result of gettimeofday() for lt and value[7], instead of
using time() for lt and gettimeofday() for value[7]
date_and_time.c |
I am sorry but I have stared at the patch and the explanation and am none the wiser :-)

There is obviously something that I am missing in the mechanics of time() and gettimeofday(). I need an explanation as to where this time shifting comes from, I think. Is it simply that time() and gettimeofday() are different? If so why?

I believe that the problem comes across because time() and gettimeofday() are separate function calls, made at slightly different times. When the returned result is calculated by assembling pieces of the results from those two calls, it may produce a value which is not within the range of either if the wrong time-counter happens to roll over in the tiny span of time between the two function calls.


At least, that's my impression from the conversation; I haven't looked at the patch in any detail.

- Brooks


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