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From Jeff Trawick <traw...@attglobal.net>
Subject Re: Conditionals...
Date Mon, 06 Aug 2001 11:33:41 GMT
"Roy T. Fielding" <fielding@ebuilt.com> writes:

> > > All variables are an approximation -- cosmic rays can change the value as
> > > well, with only a slightly smaller probability than mid-increment time
> > > slices in a non-test system.
> > 
> > hmmm... I've seen many fixes needed for several instruction sequences
> > which did not handle being interrupted (i.e. broken serialization);
> > unclear how many of the unrepeatable bugs are due to cosmic rays...
> > as a programmer I wouldn't want to assume that any of them
> > are... certainly the customers I'm familiar with would not accept that
> > as an answer :)
> Due to mid-increment time slices?  All of the race conditions I have seen
> in practice have been due to I/O operations (not register loads).

mid-increment?  I don't recall any (in the implementation language
used on the product, a special keyword on a variable declaration
caused compare-and-swap logic to be generated; very hard to screw up)

other several instruction sequences?  yep (one cause was that even
when the proper instruction sequence was known by the programmer the
compiler would sometimes play with the specified asm :( )

Jeff Trawick | trawick@attglobal.net | PGP public key at web site:
             Born in Roswell... married an alien...

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