The capstone: one workload, seven models, and the two instruments that make them comparable
capstone closes Part 14 by fixing the flaw in every chapter before it: ch50-ch55 each measured one model, with its own instrument, on its own workload, so no two numbers in the compendium were strictly comparable. Here one workload -- 8 tasks x 5000 rounds folding into a single accumulator, shared verbatim by every arm -- runs through all six models plus a sequential control, and all of them produce the identical total 0xb75768f6610642a0, which is gated before any comparison is drawn. Measured with gettid(), the three single-threaded models hold eight tasks in flight on exactly one OS thread while the four multi-threaded ones report eight. Measured with ch51's strace method, the same 40000 folds cost 1 futex call under any single-threaded model, 230 to 451 under a lock, and 51 through an Asio strand. A seventh arm settles Chapter 49's conditional promise about P2300: __cpp_lib_senders is still undefined, so it links NVIDIA's stdexec reference implementation, pinned by an in-repo Conan recipe to tag nvhpc-26.05 by sha256, isolated so the six-model core needs no Conan and no network. Verified on the Fedora 44 host: verify.lua PASS 57/FAIL 0 with Conan present and PASS 52/FAIL 0 with it hidden.
This chapter has moved. The C++ concurrency material has its own dedicated, runnable book: C++ Concurrency and Parallelism.
It maps to Full Example: Ingest, Match, Publish there.
The full, runnable C++ treatment of concurrency and parallelism — threads and jthread, mutexes and the memory model, atomics and lock-free structures, futures and coroutines, fibers, Asio, NUMA and mechanical sympathy, and the low-latency patterns — now lives in that book, each chapter with a Docker or KVM-lab demo and a Lua verify.lua behind it. This book keeps its Linux systems-programming material; the C++ concurrency compendium was extracted so it could grow on its own.