pmr
Part of the wro.cpp pmr series — 4 of 8 posts published so far.
std::pmr is one abstract class with three functions
The whole std::pmr framework is one abstract class, std::pmr::memory_resource, with three functions to override: allocate, deallocate, is_equal. A dozen-line logging resource shows a pmr::vector's allocations, then a monotonic_buffer_resource placed in front of it collapses them to zero. Episode 1 of the pmr series.
A pmr::vector on a stack buffer never calls new
The HFT and game-loop promise of pmr, made testable: override operator new to count heap allocations, then fill a pmr::vector from a monotonic_buffer_resource backed by a stack buffer with null_memory_resource upstream. Ten thousand pushes, zero heap calls. Episode 2 of the pmr series.
Does custom allocation still pay off in 2026?
Custom allocation used to buy 44 percent. A 2026 re-run of the classic study finds modern allocators like mimalloc have closed most of that gap, so a pmr arena now earns its place for predictable latency and fragmentation resilience rather than raw throughput. With a live allocation-count demo. Episode 3 of the pmr series.
Copying a pmr::vector silently drops its allocator
A pmr::vector looks like a value type, but copy construction does not copy its allocator: select_on_container_copy_construction returns the default resource, so a copied container silently allocates from the global heap. The propagation traits make the allocator sticky. Episode 4 of the pmr series.