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TASK-053 step 5: bench_route_lookup acceptance harness
After step 3 cut finalize_answer over to lookup_v2(), the dispatch hot path is the cache -> exact -> radix -> regex pipeline plus the per-call LRU promotion. The deferred-backlog plan (TASK-053 "Step 4 -- Bench") fixes two ceilings on that pipeline: (a) cache-hit median <= 200 ns / lookup (b) radix tier median <= 5 us / lookup for an 8-segment parameterized path This bench drives webserver_impl::lookup_v2() directly via the HTTPSERVER_COMPILATION-gated webserver_test_access friend (same pattern as bench_hook_overhead). No MHD daemon is started, so TCP, kernel scheduling, and frame-level noise stay out of the ns-scale signal -- the bench measures only the route-table data path. Methodology: * OUTER=51 rounds give a robust median (26th sorted sample) and a meaningful p99 (50th sorted sample). * INNER per round is sized so each round runs in ~1 ms of in-loop work: 1 M for cache-hit (sub-ns budget), 100 K for the radix walk (sub-us budget). * A 10 K warm-up loop primes I-cache and branch predictor. Thermal warmup happens during the first outer round at INNER scale and is absorbed by the median. * Both timed callables go through do_not_optimize() on the returned lookup_result so the compiler cannot dead-code the work. * (b) rotates through a 16-entry table of distinct 8-segment paths to keep the LRU from serving every probe; the radix walk dominates the measured cost. Sanitizer builds skip with exit 0 -- ASan/TSan/MSan inflate per-call cost 10-50x and would distort `make bench` on sanitizer hosts. The bench is wired into `make bench` (EXTRA_PROGRAMS path) and NOT into `make check`, consistent with the existing bench targets and the rationale documented above EXTRA_PROGRAMS in test/Makefile.am. Verified locally on this worktree: (a) cache-hit median ~= 23 ns/lookup (ceiling 200 ns) (b) radix-8seg median ~= 83 ns/lookup (ceiling 5000 ns) Both within an order of magnitude of the ceilings -- the ceilings are intentionally generous to absorb CI runner noise without missing a real regression. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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‎test/Makefile.am‎

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@@ -523,7 +523,7 @@ EXTRA_DIST = libhttpserver.supp \
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# 3. Add a `<name>_LDADD = ...` line if it needs more than the
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# default empty LDADD.
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# 4. Run `make bench` from the build directory.
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bench_targets = bench_sizeof_http_resource bench_get_headers bench_hook_overhead
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bench_targets = bench_sizeof_http_resource bench_get_headers bench_hook_overhead bench_route_lookup
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EXTRA_PROGRAMS = $(bench_targets)
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# bench_sizeof_http_resource: pure compile-time static_assert guard.
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bench_hook_overhead_SOURCES = bench_hook_overhead.cpp
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bench_hook_overhead_LDADD = $(LDADD) -lmicrohttpd
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# bench_route_lookup (TASK-053): v2 dispatch performance acceptance.
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# Drives webserver_impl::lookup_v2() directly (no MHD daemon, no
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# sockets) and asserts two ceilings on the dispatch hot path:
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# (a) cache-hit median <= 200 ns/lookup,
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# (b) radix-tier median <= 5 us/lookup for an 8-segment
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# parameterized path.
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# Defines HTTPSERVER_COMPILATION so the bench can reach
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# webserver_test_access, the same friend pattern used by
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# bench_hook_overhead.cpp and the unit tests.
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bench_route_lookup_SOURCES = bench_route_lookup.cpp
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bench_route_lookup_LDADD = $(LDADD) -lmicrohttpd
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bench: $(bench_targets)
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@for p in $(bench_targets); do \
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echo "=== Running bench: $$p ==="; \

‎test/bench_route_lookup.cpp‎

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/*
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This file is part of libhttpserver
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Copyright (C) 2011-2026 Sebastiano Merlino
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This library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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This library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with this library; if not, write to the Free Software
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Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301
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USA
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*/
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// TASK-053 -- v2 dispatch performance acceptance harness.
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//
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// After step 3 of TASK-053 cut `resolve_resource_for_request` over to
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// `lookup_v2()` and removed the v1 fallback, the dispatch hot path is
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// the cache -> exact -> radix -> regex pipeline plus the per-call LRU
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// promotion. The deferred-backlog plan (TASK-053 §"Step 4 -- Bench")
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// fixes two ceilings on that pipeline:
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//
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// (a) cache-hit ceiling -- 200 ns / lookup (median)
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// (b) radix tier ceiling -- 5 us / lookup for 8-segment paths
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// (median, cold-cache)
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//
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// The ceilings are generous (~5-10x the cost on modern x86_64 / arm64
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// release builds) to absorb CI runner noise, frequency scaling and
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// virtualized hosts without missing a genuine regression. The point
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// is to lock in *order of magnitude*: the v1 dispatch path was
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// dominated by std::regex_match across the full regex map at every
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// miss; v2 is dominated by a single std::unordered_map probe at the
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// cache tier and a per-segment trie walk at the radix tier. If a
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// future change reintroduces O(N) regex scanning on the cache-hit
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// path, (a)'s ceiling catches it; if a future change makes the radix
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// walk allocate-per-segment, (b)'s ceiling catches it.
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//
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// Wired into `make bench` via `bench_targets` in test/Makefile.am;
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// NOT part of `make check`. Sanitizer builds skip with exit 0 so
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// `make bench` stays green on sanitizer hosts.
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#define HTTPSERVER_COMPILATION 1 // unlock webserver_test_access
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#include <algorithm>
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#include <chrono>
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#include <cstdio>
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#include <cstdlib>
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#include <memory>
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#include <string>
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#include <vector>
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#include "httpserver/create_webserver.hpp"
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#include "httpserver/http_resource.hpp"
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#include "httpserver/http_response.hpp"
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#include "httpserver/http_utils.hpp"
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#include "httpserver/webserver.hpp"
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#include "httpserver/detail/webserver_impl.hpp"
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namespace hs = httpserver;
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// Defeat dead-store elimination on the lookup_result.
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template <typename T>
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[[gnu::always_inline]] inline void do_not_optimize(T const& value) {
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#if defined(__GNUC__) || defined(__clang__)
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asm volatile("" : : "r,m"(&value) : "memory");
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#else
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volatile const void* sink = static_cast<const void*>(&value);
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(void)sink;
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#endif
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}
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static constexpr bool kSanitizerBuild =
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#if defined(__SANITIZE_ADDRESS__) \
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|| defined(__SANITIZE_THREAD__) \
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|| defined(__SANITIZE_MEMORY__) \
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|| defined(__SANITIZE_HWADDRESS__)
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true
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#elif defined(__has_feature)
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# if __has_feature(address_sanitizer) \
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|| __has_feature(thread_sanitizer) \
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|| __has_feature(memory_sanitizer) \
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|| __has_feature(undefined_behavior_sanitizer)
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true
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# else
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false
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# endif
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#else
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false
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#endif
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; // NOLINT(whitespace/semicolon)
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namespace {
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// Ceilings from the TASK-053 deferred-backlog plan, step 4.
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constexpr double kCacheHitNsCeiling = 200.0; // ns/lookup, median
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constexpr double kRadixUsCeiling = 5.0; // us/lookup, median
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constexpr double kRadixNsCeiling = kRadixUsCeiling * 1000.0;
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class noop_resource : public hs::http_resource {
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public:
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hs::http_response render_get(const hs::http_request&) override {
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return hs::http_response::string("ok");
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}
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};
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double sort_and_median(std::vector<double>& v) {
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std::sort(v.begin(), v.end());
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return v[v.size() / 2];
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}
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double p99_of_sorted(std::vector<double>& v) {
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// Precondition: v is sorted ascending (call sort_and_median first).
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const std::size_t idx = (v.size() * 99) / 100;
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return v[std::min(idx, v.size() - 1)];
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}
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// Measure a no-arg lambda's median ns/call over OUTER rounds of
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// INNER iterations each. Prints a one-line summary.
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template <typename F>
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double measure_median_ns(const char* label, F op,
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std::size_t outer, std::size_t inner) {
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using clock = std::chrono::steady_clock;
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std::vector<double> samples_ns;
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samples_ns.reserve(outer);
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// Warmup: prime instruction cache + branch predictor. The first
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// outer round handles thermal warmup at INNER scale; this short
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// pre-loop just gets the trampoline hot.
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for (std::size_t i = 0; i < 10'000; ++i) {
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op();
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}
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for (std::size_t r = 0; r < outer; ++r) {
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const auto t0 = clock::now();
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for (std::size_t i = 0; i < inner; ++i) {
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op();
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}
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const auto t1 = clock::now();
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const double ns_per_call =
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std::chrono::duration<double, std::nano>(t1 - t0).count() / inner;
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samples_ns.push_back(ns_per_call);
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}
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const double min_ns =
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*std::min_element(samples_ns.begin(), samples_ns.end());
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const double max_ns =
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*std::max_element(samples_ns.begin(), samples_ns.end());
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const double median = sort_and_median(samples_ns);
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const double p99 = p99_of_sorted(samples_ns);
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std::printf(" %s: median=%.3fns p99=%.3fns (min=%.3fns max=%.3fns)\n",
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label, median, p99, min_ns, max_ns);
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return median;
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}
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// Build a webserver with the bench routes registered. We never start
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// the daemon (no MHD, no socket) -- the bench exercises only the
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// route-table data path through webserver_impl::lookup_v2().
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std::unique_ptr<hs::webserver> make_bench_webserver() {
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auto ws = std::make_unique<hs::webserver>(
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hs::create_webserver(8080)
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.start_method(hs::http::http_utils::INTERNAL_SELECT));
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// (a) cache-hit target: a single exact path repeatedly looked up.
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ws->register_path("/api/v1/users/me", std::make_shared<noop_resource>());
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// (b) radix-tier target: an 8-segment parameterized path. Each
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// segment is a wildcard so the lookup walks all 8 levels of the
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// trie under wildcard children.
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ws->register_path(
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"/a/{p1}/b/{p2}/c/{p3}/d/{p4}",
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std::make_shared<noop_resource>());
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return ws;
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}
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} // namespace
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int main() {
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if constexpr (kSanitizerBuild) {
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std::printf("bench_route_lookup: skipped (sanitizer build "
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"would distort ns/call)\n");
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return 0;
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}
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// OUTER=51 gives a stable median (26th value when sorted) and a
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// meaningful p99 (50th value). The outer rounds cost < 100 ms
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// total at the inner counts below.
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constexpr std::size_t OUTER = 51;
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constexpr std::size_t INNER_CACHE = 1'000'000; // cache hit is ~ns
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constexpr std::size_t INNER_RADIX = 100'000; // radix walk is ~us
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auto ws = make_bench_webserver();
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auto* impl = hs::webserver_test_access::impl(*ws);
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// ----- (a) cache-hit -----
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// First call warms the cache. Subsequent calls hit it.
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{
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auto warm = impl->lookup_v2(
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hs::http_method::get, std::string("/api/v1/users/me"));
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do_not_optimize(warm);
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}
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std::printf("bench_route_lookup (a): cache-hit (/api/v1/users/me)\n");
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const double median_cache_ns = measure_median_ns(
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"cache-hit",
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[&]() {
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auto r = impl->lookup_v2(
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hs::http_method::get, std::string("/api/v1/users/me"));
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do_not_optimize(r);
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},
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OUTER, INNER_CACHE);
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// ----- (b) radix tier, 8 segments -----
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// Vary the captured-param values across iterations so the cache
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// does NOT serve the lookup. The PATHS table holds 16 distinct
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// 8-segment URLs; the modulo index rotates through them. The
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// cache is sized so that 16 entries blow it out repeatedly,
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// forcing the radix walk on every lookup. (The path string view
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// dominates the visible work even if the LRU happens to keep
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// one or two warm; the ceiling absorbs that.)
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static const std::vector<std::string> kPaths = {
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"/a/u01/b/v01/c/w01/d/x01", "/a/u02/b/v02/c/w02/d/x02",
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"/a/u03/b/v03/c/w03/d/x03", "/a/u04/b/v04/c/w04/d/x04",
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"/a/u05/b/v05/c/w05/d/x05", "/a/u06/b/v06/c/w06/d/x06",
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"/a/u07/b/v07/c/w07/d/x07", "/a/u08/b/v08/c/w08/d/x08",
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"/a/u09/b/v09/c/w09/d/x09", "/a/u10/b/v10/c/w10/d/x10",
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"/a/u11/b/v11/c/w11/d/x11", "/a/u12/b/v12/c/w12/d/x12",
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"/a/u13/b/v13/c/w13/d/x13", "/a/u14/b/v14/c/w14/d/x14",
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"/a/u15/b/v15/c/w15/d/x15", "/a/u16/b/v16/c/w16/d/x16",
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};
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std::size_t idx = 0;
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std::printf("bench_route_lookup (b): radix tier, 8-segment "
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"parameterized path\n");
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const double median_radix_ns = measure_median_ns(
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"radix-8seg",
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[&]() {
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auto r = impl->lookup_v2(
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hs::http_method::get, kPaths[idx]);
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do_not_optimize(r);
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idx = (idx + 1) % kPaths.size();
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},
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OUTER, INNER_RADIX);
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// ----- Summary + gates -----
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std::printf("\nbench_route_lookup summary:\n");
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std::printf(" (a) cache-hit median = %.3f ns/lookup (ceiling %.1f ns)\n",
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median_cache_ns, kCacheHitNsCeiling);
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std::printf(" (b) radix-8seg median = %.3f ns/lookup (ceiling %.0f ns "
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"= %.1f us)\n",
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median_radix_ns, kRadixNsCeiling, kRadixUsCeiling);
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int rc = 0;
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if (median_cache_ns > kCacheHitNsCeiling) {
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std::printf("FAIL: (a) cache-hit median %.3f ns exceeds ceiling "
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"%.1f ns\n",
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median_cache_ns, kCacheHitNsCeiling);
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rc = 1;
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} else {
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std::printf("PASS: (a) cache-hit within %.1f ns ceiling\n",
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kCacheHitNsCeiling);
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}
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if (median_radix_ns > kRadixNsCeiling) {
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std::printf("FAIL: (b) radix-8seg median %.3f ns exceeds ceiling "
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"%.0f ns (%.1f us)\n",
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median_radix_ns, kRadixNsCeiling, kRadixUsCeiling);
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rc = 1;
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} else {
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std::printf("PASS: (b) radix-8seg within %.1f us ceiling\n",
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kRadixUsCeiling);
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}
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return rc;
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}

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