[libc++][test] Add stop_token benchmark (#69117)

This is transforming the `stop_token` benchmark that Lewis Baker had
created into Google
Bench
https://reviews.llvm.org/D154702

libcxx/benchmarks/CMakeLists.txt

@@ -213,6 +213,7 @@ set(BENCHMARK_TESTS
     map.bench.cpp
     monotonic_buffer.bench.cpp
     ordered_set.bench.cpp
+    stop_token.bench.cpp
     std_format_spec_string_unicode.bench.cpp
     string.bench.cpp
     stringstream.bench.cpp

libcxx/benchmarks/stop_token.bench.cpp

@@ -0,0 +1,108 @@
+//===----------------------------------------------------------------------===//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include <numeric>
+#include <stop_token>
+#include <thread>
+
+#include "benchmark/benchmark.h"
+#include "make_test_thread.h"
+
+using namespace std::chrono_literals;
+
+// We have a single thread created by std::jthread consuming the stop_token:
+// registering/deregistering callbacks, one at a time.
+void BM_stop_token_single_thread_reg_unreg_callback(benchmark::State& state) {
+  auto thread_func = [&](std::stop_token st, std::atomic<std::uint64_t>* reg_count) {
+    while (!st.stop_requested()) {
+      std::stop_callback cb{st, [&]() noexcept {}};
+      benchmark::DoNotOptimize(cb);
+      reg_count->fetch_add(1, std::memory_order_relaxed);
+    }
+  };
+
+  std::atomic<std::uint64_t> reg_count(0);
+  std::uint64_t total_reg_test_param = state.range(0);
+
+  auto thread = support::make_test_jthread(thread_func, &reg_count);
+
+  for (auto _ : state) {
+    auto start_total = reg_count.load(std::memory_order_relaxed);
+
+    while (reg_count.load(std::memory_order_relaxed) - start_total < total_reg_test_param) {
+      std::this_thread::yield();
+    }
+  }
+}
+BENCHMARK(BM_stop_token_single_thread_reg_unreg_callback)->RangeMultiplier(2)->Range(1 << 10, 1 << 24);
+
+// At startup, it creates a single stop_source which it will then pass an associated stop_token to every
+// request.
+//
+// Assume a thread-pool handles these requests and for each request it polls for stop_requested(), then attaches a
+// stop-callback, does some work, then detaches the stop-callback some time later. The lifetime of requests/callbacks
+// would overlap with other requests/callback from the same thread.
+//
+// Say something like each thread keeping a circular buffer of N stop-callbacks and destroying the stop-callbacks in
+// FIFO order
+void BM_stop_token_async_reg_unreg_callback(benchmark::State& state) {
+  struct dummy_stop_callback {
+    void operator()() const noexcept {}
+  };
+
+  constexpr size_t thread_count             = 20;
+  constexpr size_t concurrent_request_count = 1000;
+  std::atomic<bool> start{false};
+
+  std::uint64_t total_reg_test_param = state.range(0);
+
+  std::stop_source ss;
+  std::vector<std::jthread> threads;
+  threads.reserve(thread_count);
+  std::vector<std::atomic<std::uint64_t>> reg_counts(thread_count);
+
+  auto thread_func = [&start](std::atomic<std::uint64_t>* count, std::stop_token st) {
+    std::vector<std::optional<std::stop_callback<dummy_stop_callback>>> cbs(concurrent_request_count);
+
+    start.wait(false);
+
+    std::uint32_t index = 0;
+    while (!st.stop_requested()) {
+      cbs[index].emplace(st, dummy_stop_callback{});
+      index = (index + 1) % concurrent_request_count;
+      count->fetch_add(1, std::memory_order_relaxed);
+    }
+  };
+
+  for (size_t i = 0; i < thread_count; ++i) {
+    threads.emplace_back(support::make_test_jthread(thread_func, &reg_counts[i], ss.get_token()));
+  }
+
+  auto get_total_reg = [&] {
+    std::uint64_t total = 0;
+    for (const auto& reg_counts : reg_counts) {
+      total += reg_counts.load(std::memory_order_relaxed);
+    }
+    return total;
+  };
+
+  start = true;
+  start.notify_all();
+
+  for (auto _ : state) {
+    auto start_total = get_total_reg();
+
+    while (get_total_reg() - start_total < total_reg_test_param) {
+      std::this_thread::yield();
+    }
+  }
+
+  ss.request_stop();
+}
+BENCHMARK(BM_stop_token_async_reg_unreg_callback)->RangeMultiplier(2)->Range(1 << 10, 1 << 24);
+
+BENCHMARK_MAIN();