My guess is the existing behavior was designed to allow waking of multiple waiters _sometimes_ without starving of exclusive waiters.
Well, I think the current algorithm *does* allow starvation, at least in some situations. Consider a workload in which a new shared reader arrives every 50 ms, and holds the lock for, say, 500 ms. If an exclusive waiter arrives, they will starve with the current algorithm.
There should be a comment in the code explaining this usage and I bet it was intentional.
Oh, I bet it was intentional as well :) I'm mostly curious to see exactly what the reasoning was, and whether it is necessary that we preserve the FIFO behavior while considering optimizations.
-Neil
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