In message <[EMAIL PROTECTED]>, Mike Smith writes:
>> Yesterday I was looking at how Linux handles the gettimeofday stuff
>> without locking thier sys_tz variable, well it seems they don't care
>> or I'm missing something important.
>>
>> They just don't lock it, not that settimeofday will be called all that
>> often but it leaves me wondering what we can do about this, effectively
>> we can pack our tz (sys_tz in Linux) into a 32bit value which should
>> afford us read/write atomicity on every platform I'm aware of.
>>
>> In fact this can be quite effective for certain types of data structures,
>> even though our 'struct timezone' is two ints we can pack it into two
>> uint16 and pack a private structure, then copy it to a stack and expand
>> it into the user's address space.
>
>It would be cheaper just to lock the bloody thing, although you can't
>pack all the significance of a timeval into 16 bits anyway (in a fashion
>that's going to make many people happy).
Or do the "stable-storage" thing with it, and just grab a copy of the
pointer (which will be an atomic op). See timecounters for an example.
--
Poul-Henning Kamp FreeBSD coreteam member
[EMAIL PROTECTED] "Real hackers run -current on their laptop."
FreeBSD -- It will take a long time before progress goes too far!
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