Couroutine NRVO benchmark

Reviewed By: lewissbaker

Differential Revision: D9354535

fbshipit-source-id: 49c228e773f21a2fcfa4701eec4cb4dc76c2f990

folly/experimental/coro/test/CoroBenchmarkNRVO.cpp

+/*
+ * Copyright 2018-present Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <folly/Benchmark.h>
+
+#if FOLLY_HAS_COROUTINES
+#include <experimental/coroutine>
+#include <future>
+
+class Wait {
+ public:
+  class promise_type {
+   public:
+    Wait get_return_object() {
+      return Wait(promise_.get_future());
+    }
+
+    std::experimental::suspend_never initial_suspend() {
+      return {};
+    }
+
+    std::experimental::suspend_never final_suspend() {
+      return {};
+    }
+
+    void return_void() {
+      promise_.set_value();
+    }
+
+    void unhandled_exception() {
+      promise_.set_exception(std::current_exception());
+    }
+
+   private:
+    std::promise<void> promise_;
+  };
+
+  explicit Wait(std::future<void> future) : future_(std::move(future)) {}
+
+  Wait(Wait&&) = default;
+
+  void detach() {
+    future_ = {};
+  }
+
+  ~Wait() {
+    if (future_.valid()) {
+      future_.get();
+    }
+  }
+
+ private:
+  std::future<void> future_;
+};
+
+template <typename T>
+class InlineTask {
+ public:
+  InlineTask(const InlineTask&) = delete;
+  InlineTask(InlineTask&& other)
+      : promise_(std::exchange(other.promise_, nullptr)) {}
+
+  ~InlineTask() {
+    DCHECK(!promise_);
+  }
+
+  bool await_ready() const {
+    return false;
+  }
+
+  std::experimental::coroutine_handle<> await_suspend(
+      std::experimental::coroutine_handle<> awaiter) {
+    promise_->valuePtr_ = &value_;
+    promise_->awaiter_ = std::move(awaiter);
+    return std::experimental::coroutine_handle<promise_type>::from_promise(
+        *promise_);
+  }
+
+  T await_resume() {
+    std::experimental::coroutine_handle<promise_type>::from_promise(
+        *std::exchange(promise_, nullptr))
+        .destroy();
+    T value = std::move(value_);
+    return value;
+  }
+
+  class promise_type {
+   public:
+    InlineTask get_return_object() {
+      return InlineTask(this);
+    }
+
+    template <typename U>
+    void return_value(U&& value) {
+      *valuePtr_ = std::forward<U>(value);
+    }
+
+    void unhandled_exception() {
+      std::terminate();
+    }
+
+    std::experimental::suspend_always initial_suspend() {
+      return {};
+    }
+
+    class FinalSuspender {
+     public:
+      explicit FinalSuspender(std::experimental::coroutine_handle<> awaiter)
+          : awaiter_(std::move(awaiter)) {}
+
+      bool await_ready() {
+        return false;
+      }
+
+      auto await_suspend(std::experimental::coroutine_handle<>) {
+        return awaiter_;
+      }
+
+      void await_resume() {}
+
+     private:
+      std::experimental::coroutine_handle<> awaiter_;
+    };
+
+    FinalSuspender final_suspend() {
+      return FinalSuspender(std::move(awaiter_));
+    }
+
+   private:
+    friend class InlineTask;
+
+    T* valuePtr_;
+    std::experimental::coroutine_handle<> awaiter_;
+  };
+
+ private:
+  friend class promise_type;
+
+  explicit InlineTask(promise_type* promise) : promise_(promise) {}
+
+  T value_;
+  promise_type* promise_;
+};
+
+struct ExpensiveCopy {
+  ExpensiveCopy() {}
+
+  ExpensiveCopy(const ExpensiveCopy&) {
+    std::this_thread::sleep_for(std::chrono::milliseconds{1});
+  }
+};
+
+InlineTask<ExpensiveCopy> co_nestedCalls(size_t times) {
+  ExpensiveCopy ret;
+  if (times > 0) {
+    ret = co_await co_nestedCalls(times - 1);
+  }
+  co_return ret;
+}
+
+void coroNRVO(size_t times, size_t iters) {
+  for (size_t iter = 0; iter < iters; ++iter) {
+    [](size_t times) -> Wait {
+      (void)co_await co_nestedCalls(times);
+      co_return;
+    }(times);
+  }
+}
+
+BENCHMARK(coroNRVOOneAwait, iters) {
+  coroNRVO(1, iters);
+}
+
+BENCHMARK(coroNRVOTenAwaits, iters) {
+  coroNRVO(10, iters);
+}
+#endif
+
+ExpensiveCopy nestedCalls(size_t times) {
+  ExpensiveCopy ret;
+  if (times > 0) {
+    ret = nestedCalls(times - 1);
+  }
+
+  return ret;
+}
+
+void NRVO(size_t times, size_t iters) {
+  for (size_t iter = 0; iter < iters; ++iter) {
+    nestedCalls(times);
+  }
+}
+
+BENCHMARK(NRVOOneAwait, iters) {
+  NRVO(1, iters);
+}
+
+BENCHMARK(NRVOTenAwaits, iters) {
+  NRVO(10, iters);
+}
+
+int main(int argc, char** argv) {
+  gflags::ParseCommandLineFlags(&argc, &argv, true);
+  folly::runBenchmarks();
+  return 0;
+}