SF: Add promise/future utilities (8e89c2ad) · Commits · e / os / android_frameworks_native

services/surfaceflinger/Promise.h

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		/*
		* Copyright 2020 The Android Open Source Project
		*
		* 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.
		*/

		#pragma once

		#include <future>
		#include <type_traits>
		#include <utility>

		namespace android::promise {
		namespace impl {

		template <typename T>
		struct FutureResult {
		using Type = T;
		};

		template <typename T>
		struct FutureResult<std::future<T>> {
		using Type = T;
		};

		} // namespace impl

		template <typename T>
		using FutureResult = typename impl::FutureResult<T>::Type;

		template <typename... Args>
		inline auto defer(Args... args) {
		return std::async(std::launch::deferred, std::forward<Args>(args)...);
		}

		template <typename T>
		inline std::future<T> yield(T&& v) {
		return defer([](T&& v) { return std::forward<T>(v); }, std::forward<T>(v));
		}

		template <typename T>
		struct Chain {
		Chain(std::future<T>&& f) : future(std::move(f)) {}
		operator std::future<T>&&() && { return std::move(future); }

		T get() && { return future.get(); }

		template <typename F, typename R = std::invoke_result_t<F, T>>
		auto then(F&& op) && -> Chain<FutureResult<R>> {
		return defer(
		[](auto&& f, F&& op) {
		R r = op(f.get());
		if constexpr (std::is_same_v<R, FutureResult<R>>) {
		return r;
		} else {
		return r.get();
		}
		},
		std::move(future), std::forward<F>(op));
		}

		std::future<T> future;
		};

		template <typename T>
		inline Chain<T> chain(std::future<T>&& f) {
		return std::move(f);
		}

		} // namespace android::promise

services/surfaceflinger/tests/unittests/Android.bp

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		@@ -48,6 +48,7 @@ cc_test {
		"LayerHistoryTestV2.cpp",
		"LayerMetadataTest.cpp",
		"PhaseOffsetsTest.cpp",
		"PromiseTest.cpp",
		"SchedulerTest.cpp",
		"SchedulerUtilsTest.cpp",
		"SetFrameRateTest.cpp",

services/surfaceflinger/tests/unittests/PromiseTest.cpp

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		/*
		* Copyright 2020 The Android Open Source Project
		*
		* 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 <algorithm>
		#include <future>
		#include <string>
		#include <thread>
		#include <vector>

		#include <gtest/gtest.h>

		#include "Promise.h"

		namespace android {
		namespace {

		using Bytes = std::vector<uint8_t>;

		Bytes decrement(Bytes bytes) {
		std::transform(bytes.begin(), bytes.end(), bytes.begin(), [](auto b) { return b - 1; });
		return bytes;
		}

		} // namespace

		TEST(PromiseTest, yield) {
		EXPECT_EQ(42, promise::yield(42).get());

		auto ptr = std::make_unique<char>('!');
		auto future = promise::yield(std::move(ptr));
		EXPECT_EQ('!', *future.get());
		}

		TEST(PromiseTest, chain) {
		std::packaged_task<const char*()> fetchString([] { return "ifmmp-"; });

		std::packaged_task<Bytes(std::string)> appendString([](std::string str) {
		str += "!xpsme";
		return Bytes{str.begin(), str.end()};
		});

		std::packaged_task<std::future<Bytes>(Bytes)> decrementBytes(
		[](Bytes bytes) { return promise::defer(decrement, std::move(bytes)); });

		auto fetch = fetchString.get_future();
		std::thread fetchThread(std::move(fetchString));

		std::thread appendThread, decrementThread;

		EXPECT_EQ("hello, world",
		promise::chain(std::move(fetch))
		.then([](const char* str) { return std::string(str); })
		.then([&](std::string str) {
		auto append = appendString.get_future();
		appendThread = std::thread(std::move(appendString), std::move(str));
		return append;
		})
		.then([&](Bytes bytes) {
		auto decrement = decrementBytes.get_future();
		decrementThread = std::thread(std::move(decrementBytes),
		std::move(bytes));
		return decrement;
		})
		.then([](std::future<Bytes> bytes) { return bytes; })
		.then([](const Bytes& bytes) {
		return std::string(bytes.begin(), bytes.end());
		})
		.get());

		fetchThread.join();
		appendThread.join();
		decrementThread.join();
		}

		} // namespace android