API Reference — pma/resources/ArenaMemoryResource

class ArenaMemoryResource : public MemoryResource

Serves allocations from a preallocated memory region instead of hitting the upstream allocator on every request.

Why this exists

Arena allocation amortizes the cost of many small allocations into a few large upstream requests, and lets a whole set of related allocations be released together implicitly (deallocate is a no-op — the arena frees everything when it itself is destroyed). When the active region runs out of space, an additional region is allocated and scaled by growthFactor, so the arena grows without requiring the caller to size it perfectly up front.

Construction

// initial region sized separately from subsequent growth regions, 1.5x growth per new region
pma::ArenaMemoryResource arena{/*initialSize=*/4096, /*regionSize=*/1024, /*growthFactor=*/1.5f, upstream};

// simpler form: same regionSize used for initial and all subsequent regions, no growth
pma::ArenaMemoryResource fixedArena{/*regionSize=*/1024, upstream};

Relationships

  • MemoryResource — base interface ArenaMemoryResource implements.
  • ScopedPtr / FactoryDestroy — used internally to manage the arena's private Impl.

Constraints

  • Not copyable — copy constructor and copy assignment are deleted.
  • Move-only: supports move construction and move assignment.
  • deallocate is a no-op; regions are only freed when the arena itself is destroyed.
  • Region allocation sequence follows the geometric series: {initialSize, regionSize, regionSize × growthFactor, regionSize × growthFactor², …}. When initialSize is omitted, the first region is also regionSize.
  • The upstream pointer must remain valid for the entire lifetime of the ArenaMemoryResource.

Watch out for

  • deallocate is a no-op. Calling it does not free any memory. All memory held by the arena is released only when the ArenaMemoryResource object is destroyed or goes out of scope. Do not rely on individual frees for resource management.
  • Copy construction and copy assignment are deleted. ArenaMemoryResource is move-only — transfer ownership with std::move rather than copying.