On Monday, 26 June 2000 at 20:00:09 -0400, Daniel Eischen wrote:

I find this rather strange. There can be many reasons to take a mutex, and not all of them have to be fast. Even in the case where they are, it doesn't seem to be of any value to wake more processes than can take the mutex. From http://www.sunworld.com/sunworldonline/swol-08-1999/swol-08-insidesolaris-2.html:

Sun engineering coded the turnstile_wakeup() in Solaris 7 in a generic enough way so that a single thread wakeup could be executed, instead of all threads inevitably waking up together. Exhaustive testing under a variety of different loads has shown that, in practice, we very rarely end up with a large blocking chain of threads, and thus almost never run into the thundering herd problem. The wakeup-all implementation also solves some bit synchronization issues that make a wakeup-one scenario tricky.

This seems like a less honest way of saying "We couldn't figure out how to avoid race conditions on wakeup, and so far nobody has been able to point to a thundering herd". I'd need some conviction.

Greg

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