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//===----------------------------------------------------------------------===//
// 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
//
//===----------------------------------------------------------------------===//
// To run this test, build libcxx and cxx-benchmarks targets
// cd third-party/benchmark/tools
// ./compare.py filters ../../../build/libcxx/benchmarks/atomic_wait_vs_mutex_lock.libcxx.out BM_atomic_wait BM_mutex
#include <atomic>
#include <mutex>
#include <numeric>
#include <thread>
#include "benchmark/benchmark.h"
#include "make_test_thread.h"
using namespace std::chrono_literals;
struct AtomicLock {
std::atomic<bool>& locked_;
AtomicLock(const AtomicLock&) = delete;
AtomicLock& operator=(const AtomicLock&) = delete;
AtomicLock(std::atomic<bool>& l) : locked_(l) { lock(); }
~AtomicLock() { unlock(); }
void lock() {
while (true) {
locked_.wait(true, std::memory_order_relaxed);
bool expected = false;
if (locked_.compare_exchange_weak(expected, true, std::memory_order_acquire, std::memory_order_relaxed))
break;
}
}
void unlock() {
locked_.store(false, std::memory_order_release);
locked_.notify_all();
}
};
// using LockState = std::atomic<bool>;
// using Lock = AtomicLock;
// using LockState = std::mutex;
// using Lock = std::unique_lock<std::mutex>;
template <class LockState, class Lock>
void test_multi_thread_lock_unlock(benchmark::State& state) {
std::uint64_t total_loop_test_param = state.range(0);
constexpr auto num_threads = 15;
std::vector<std::jthread> threads;
threads.reserve(num_threads);
std::atomic<std::uint64_t> start_flag = 0;
std::atomic<std::uint64_t> done_count = 0;
LockState lock_state{};
auto func = [&start_flag, &done_count, &lock_state, total_loop_test_param](std::stop_token st) {
auto old_start = 0;
while (!st.stop_requested()) {
start_flag.wait(old_start);
old_start = start_flag.load();
// main things under test: locking and unlocking in the loop
for (std::uint64_t i = 0; i < total_loop_test_param; ++i) {
Lock l{lock_state};
}
done_count.fetch_add(1);
}
};
for (size_t i = 0; i < num_threads; ++i) {
threads.emplace_back(support::make_test_jthread(func));
}
for (auto _ : state) {
done_count = 0;
start_flag.fetch_add(1);
start_flag.notify_all();
while (done_count < num_threads) {
std::this_thread::yield();
}
}
for (auto& t : threads) {
t.request_stop();
}
start_flag.fetch_add(1);
start_flag.notify_all();
for (auto& t : threads) {
t.join();
}
}
void BM_atomic_wait(benchmark::State& state) { test_multi_thread_lock_unlock<std::atomic<bool>, AtomicLock>(state); }
BENCHMARK(BM_atomic_wait)->RangeMultiplier(2)->Range(1 << 10, 1 << 20);
void BM_mutex(benchmark::State& state) {
test_multi_thread_lock_unlock<std::mutex, std::unique_lock<std::mutex>>(state);
}
BENCHMARK(BM_mutex)->RangeMultiplier(2)->Range(1 << 10, 1 << 20);
BENCHMARK_MAIN();
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