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Update potential misunderstanding about thread safety

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This commit is contained in:
Andrew Noyes
2025-08-29 14:08:41 -04:00
parent 62b37c067c
commit a5776004de
3 changed files with 45 additions and 52 deletions
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32
benchmarks/bench_metric.cpp
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@@ -58,9 +58,6 @@ struct ContentionEnvironment {
bg_counter.inc(1.0);
bg_gauge.set(dist(rng));
bg_histogram.observe(dist(rng));
// Small delay to avoid spinning too fast
std::this_thread::sleep_for(std::chrono::microseconds(1));
}
});
}
@@ -74,8 +71,6 @@ struct ContentionEnvironment {
auto output = metric::render(arena);
static_cast<void>(output); // Suppress unused variable warning
arena.reset();
std::this_thread::sleep_for(std::chrono::microseconds(100));
}
});
}
@@ -140,9 +135,6 @@ int main() {
// Start background threads creating contention
env.start_background_contention(8);
std::this_thread::sleep_for(
std::chrono::milliseconds(100)); // Let background threads start
bench.run("counter.inc() - 8 background threads", [&]() {
env.counter.inc(1.0);
ankerl::nanobench::doNotOptimizeAway(env.counter);
@@ -172,8 +164,6 @@ int main() {
env.start_background_contention(4);
env.start_render_thread();
std::this_thread::sleep_for(std::chrono::milliseconds(100));
bench.run("counter.inc() - with concurrent render", [&]() {
env.counter.inc(1.0);
ankerl::nanobench::doNotOptimizeAway(env.counter);
@@ -192,29 +182,28 @@ int main() {
// Shared gauge contention
{
// Test the multi-writer CAS behavior of gauges
// Test the multi-writer CAS behavior of gauges when multiple threads
// create gauges with the same labels. They will all point to the same
// underlying state, causing high contention.
auto gauge_family =
metric::create_gauge("shared_gauge", "Shared gauge test");
auto shared_gauge = gauge_family.create({{"shared", "true"}});
// Background threads all writing to the SAME gauge (high CAS contention)
std::atomic<bool> stop_shared{false};
std::vector<std::thread> shared_threads;
for (int i = 0; i < 8; ++i) {
shared_threads.emplace_back([&shared_gauge, &stop_shared]() {
shared_threads.emplace_back([&gauge_family, &stop_shared]() {
auto gauge = gauge_family.create({{"shared", "true"}});
while (!stop_shared.load(std::memory_order_relaxed)) {
shared_gauge.inc(1.0);
std::this_thread::sleep_for(std::chrono::nanoseconds(100));
gauge.inc(1.0);
}
});
}
std::this_thread::sleep_for(std::chrono::milliseconds(50));
bench.run("gauge.inc() - 8 threads same gauge (CAS contention)", [&]() {
shared_gauge.inc(1.0);
ankerl::nanobench::doNotOptimizeAway(shared_gauge);
auto gauge_for_benchmark = gauge_family.create({{"shared", "true"}});
bench.run("gauge.inc() - 8 threads, same labels (contention)", [&]() {
gauge_for_benchmark.inc(1.0);
ankerl::nanobench::doNotOptimizeAway(gauge_for_benchmark);
});
stop_shared.store(true);
@@ -292,7 +281,6 @@ int main() {
while (!stop_callback.load()) {
counter_value.fetch_add(1);
gauge_value.store(gauge_value.load() + 1);
std::this_thread::sleep_for(std::chrono::microseconds(10));
}
});