greg7mdp/parallel-hashmap

Health v2 · maintenance only

Adoption not part of the score

3211 stars · 311 forks observed · 2026-08-28

What it is AI-extracted, prompt v1, taxonomy v1, 2026-08-29, confidence not recorded

A family of header-only C++ hash map/set and btree containers that serve as fast, memory-friendly drop-in replacements for std::unordered_map, std::unordered_set, std::map, and std::set. Its parallel variants support high-concurrency access from multiple threads while keeping a low memory footprint.

Use cases

• replace std::unordered_map with a faster, lower-memory hashmap
• share a hash map across multiple threads with high concurrency
• store large key-value datasets with minimal memory overhead
• dump and reload a flat hash map to disk very quickly
• use a btree alternative to std::map and std::set
• forward declare map containers in headers without heavy includes

When to choose

• you need a drop-in C++11+ replacement for standard hash or ordered containers with better speed and memory usage
• your workload reads and writes a shared map from many threads
• you want header-only integration with no build step
• you need fast bulk serialization of trivially-copyable flat maps

When to avoid

• you can adopt C++20 and prefer the successor gtl library with ongoing feature development
• you need node-based guarantees or exotic allocator requirements beyond what phmap supports
• you rely on pointer-key forward declarations, which are not supported by phmap_fwd_decl.h

Facets

library · maturity maintenance

caching serialization concurrency developer-tools performance databases cpp cross-platform windows header-only hashmap btree drop-in-replacement multithreaded memory-efficient abseil-inspired algorithms linux macos

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