Chris Wellons • 5/6/2026

Concurrent, atomic MSI hash tables

This article discusses how to add atomic operations to Mask-Step-Index (MSI) hash tables to support concurrent access, specifically for a single-producer, multiple-consumer (SPMC) scenario. It covers the implementation of integer hash sets with no deletions, using relaxed atomic loads and stores to avoid data races while tolerating out-of-order insertions. The article provides code examples for both insertion and lookup functions, explaining the use of GCC atomic built-ins to ensure thread safety without requiring special type qualifiers.

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#data structures #c programming #Atomic Operations