Reader-Writer Lock versus Mutex - Understanding a Lost Bet

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Mutexes have frequently been observed to outperform reader-writer locks in domains where, logically, reader-writer locks should dominate. I was recently given an opportunity to address this inconsistency and, to demonstrate my certainty of success, accepted a bet regarding outperforming a mutex for a high read, low write work task with short — but not extremely short — lock hold times. I lost the bet. I resolved to understand how I lost this bet and, in my mind at least, convert this "loss" to a "win". The bet focused on a Linux platform (the evaluations presented are multi-platform). This presentation will discuss design criteria for a reader-writer lock, the "losing" implementation, the performance results for the "losing" implementation, a possible explanation for the loss, the novel "winning" implementation, and the results supporting the value of the "winning" implementation. A basic understanding of mutexes, reader-writer locks, and atomic operations is recommended for attendees.



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