Read-write semaphores should never be used. As others have pointed out,
they cause really intractable priority inversion problems (because a
high priority writer will often have to wait for an unbounded number of
lower priority readers, some of which may have called a blocking
function while holding the read lock).
Note that I'm not talking about read-write spinlocks, which are (or
should be) held for a short, bounded time and can't be held over a
blocking call, so they are not quite so problematic.
Nigel Gamble nigel@nrg.org
Mountain View, CA, USA. http://www.nrg.org/
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