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From: Alexander Terekhov (terekhov_at_[hidden])
Date: 2008-04-21 15:10:32

Peter Dimov wrote:
> >>> shared_mutex is not designed for this scenario, since you have high
> >>> contention. shared_mutex is designed for infrequent updates.
> Some more observations.
> The same writer starvation occurs with 2 reader threads, so it's not caused
> by the overcommit. Two reader threads on two cores is common.
> The update frequency doesn't matter; a lower update frequency would just
> scale the time it takes to perform 1M updates, it will not change the
> average writer wait time.
> Some wait times (2R+1W):
> atomics: 7.673 microseconds
> lightweight_mutex (CRITICAL_SECTION): 3.069 us
> shared_mutex: 760 us
> rw_mutex (my implementation): 665 us (same problem)
> pthread_rwlock_t, pthreads-win32: 7.108 us
> rw_mutex (Hinnant/Terekhov): 85.532 us
> This last line uses my reimplementation of Howard Hinnant's read/write mutex
> based on his description; Howard credits Alexander Terekhov with the
> original algorithm. It does stall the writer a bit in exchange for optimal
> reader throughput, but doesn't suffer from outright starvation.

See pthreads-win32 for the original algorithm (except support for static
init stuff).


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