Subj : Re: posix and lock-free algorithms
To   : comp.programming.threads
From : John Doug Reynolds
Date : Thu Aug 11 2005 09:12 pm

> "Applications shall ensure that access to any memory location by
>  more than one thread of control (threads or processes) is restricted
>  such that no thread of control can read or modify a memory location
>  while another thread of control may be modifying it."

The implication of this quote has finally gotten through to me, I
think.  I imagined that as long as the write to a memory location is
known to be atomic, there is no requirement to avoid simultaneously
reading that location.  DCSI seeks to allow simultaneous read and
write, and tries ensure that this can be done safely.  And this might
even be possible on a given architecture, but that's irrelevant within
the Posix framework.  The very attempt to write such an algorithm
defies Posix--to ask whether this can be accomplished under Posix is
to miss the point entirely.

It may be possible to implement DCSI.  It may even be possible to
implement it portably, though such an implementation will not rely on
Posix.  A particular language might enable the portable use of DCSI.
C/C++ is not such a language.

Well, I think this is what you all have been patiently trying to tell
me.  Many thanks,

Doug

.