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build --cxxopt=-std=c++17 --host_cxxopt=-std=c++17 --incompatible_java_common_parameters=false --define=android_dexmerger_tool=d8_dexmerger --define=android_incremental_dexing_tool=d8_dexbuilder --nouse_workers_with_dexbuilder | ||
build --cxxopt=-std=c++17 --cxxopt=-fcoroutines-ts --host_cxxopt=-std=c++17 --host_cxxopt=-fcoroutines-ts --incompatible_java_common_parameters=false --define=android_dexmerger_tool=d8_dexmerger --define=android_incremental_dexing_tool=d8_dexbuilder --nouse_workers_with_dexbuilder |
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/** | ||
* Copyright 2021 Snap, 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. | ||
*/ | ||
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#pragma once | ||
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#include "Future.hpp" | ||
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#include <memory> | ||
#include <optional> | ||
#include <type_traits> | ||
#include <variant> | ||
#include <vector> | ||
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namespace djinni { | ||
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// SharedFuture is a wrapper around djinni::Future to allow multiple consumers (i.e. like std::shared_future) | ||
// The API is designed to be similar to djinni::Future. | ||
template<typename T> | ||
class SharedFuture { | ||
public: | ||
// Create SharedFuture from Future. Runtime error if the future is already consumed. | ||
explicit SharedFuture(Future<T>&& future); | ||
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// Transform into Future<T>. | ||
Future<T> toFuture() const { | ||
if (await_ready()) { | ||
co_return await_resume(); // return stored value directly | ||
} | ||
co_return co_await SharedFuture(*this); // retain copy during coroutine suspension | ||
} | ||
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void wait() const { | ||
return [this]() -> Future<void> { co_await *this; }().wait(); | ||
} | ||
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decltype(auto) get() const { | ||
wait(); | ||
return await_resume(); | ||
} | ||
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// Transform the result of this future into a new future. The behavior is same as Future::then except that | ||
// it doesn't consume the future, and can be called multiple times. | ||
template<typename Func> | ||
SharedFuture<std::remove_cv_t<std::remove_reference_t<std::invoke_result_t<Func, T>>>> then(Func transform) const { | ||
co_return transform(co_await SharedFuture(*this)); // retain copy during coroutine suspension | ||
} | ||
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// Overload for T = void or `transform` takes no arugment. | ||
template<typename Func, typename = std::enable_if_t<!std::is_invocable_v<Func, T>>> | ||
SharedFuture<std::remove_cv_t<std::remove_reference_t<std::invoke_result_t<Func>>>> then(Func transform) const { | ||
co_await SharedFuture(*this); // retain copy during coroutine suspension | ||
co_return transform(); | ||
} | ||
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// -- coroutine support implementation only; not intended externally -- | ||
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bool await_ready() const { | ||
std::scoped_lock lock(_sharedStates->mutex); | ||
return _sharedStates->storedValue.has_value(); | ||
} | ||
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decltype(auto) await_resume() const { | ||
if constexpr (!std::is_void_v<T>) { | ||
return *_sharedStates->storedValue; | ||
} | ||
} | ||
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bool await_suspend(detail::CoroutineHandle<> h) const; | ||
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struct Promise : public Future<T>::promise_type { | ||
SharedFuture<T> get_return_object() noexcept { | ||
return SharedFuture(Future<T>::promise_type::get_return_object()); | ||
} | ||
}; | ||
using promise_type = Promise; | ||
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private: | ||
struct SharedStates { | ||
std::recursive_mutex mutex; | ||
std::optional<std::conditional_t<std::is_void_v<T>, std::monostate, T>> storedValue = std::nullopt; | ||
std::vector<detail::CoroutineHandle<>> coroutineHandles; | ||
}; | ||
// Use a shared_ptr to allow copying SharedFuture. | ||
std::shared_ptr<SharedStates> _sharedStates = std::make_shared<SharedStates>(); | ||
}; | ||
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// CTAD deduction guide to construct from Future directly. | ||
template<typename T> | ||
SharedFuture(Future<T>&&) -> SharedFuture<T>; | ||
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// ------------------ Implementation ------------------ | ||
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template<typename T> | ||
SharedFuture<T>::SharedFuture(Future<T>&& future) { | ||
// `future` will invoke all continuations when it is ready. | ||
future.then([sharedStates = _sharedStates](auto futureResult) { | ||
std::vector toCall = [&] { | ||
std::scoped_lock lock(sharedStates->mutex); | ||
if constexpr (std::is_void_v<T>) { | ||
sharedStates->storedValue.emplace(); | ||
} else { | ||
sharedStates->storedValue = futureResult.get(); | ||
} | ||
return std::move(sharedStates->coroutineHandles); | ||
}(); | ||
for (auto& handle : toCall) { | ||
handle(); | ||
} | ||
}); | ||
} | ||
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template<typename T> | ||
bool SharedFuture<T>::await_suspend(detail::CoroutineHandle<> h) const { | ||
{ | ||
std::unique_lock lock(_sharedStates->mutex); | ||
if (!_sharedStates->storedValue) { | ||
_sharedStates->coroutineHandles.push_back(std::move(h)); | ||
return true; | ||
} | ||
} | ||
h(); | ||
return true; | ||
} | ||
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} // namespace djinni |
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61
test-suite/handwritten-src/objc/tests/DBSharedFutureTest.mm
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#import <Foundation/Foundation.h> | ||
#import <XCTest/XCTest.h> | ||
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#include "../../../support-lib/cpp/SharedFuture.hpp" | ||
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@interface DBSharedFutureTest : XCTestCase | ||
@end | ||
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@implementation DBSharedFutureTest | ||
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- (void)setUp | ||
{ | ||
[super setUp]; | ||
} | ||
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- (void)tearDown | ||
{ | ||
[super tearDown]; | ||
} | ||
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- (void)testCreateFuture | ||
{ | ||
djinni::SharedFuture<int> resolvedInt(djinni::Promise<int>::resolve(42)); | ||
XCTAssertEqual(resolvedInt.get(), 42); | ||
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djinni::Promise<NSString*> strPromise; | ||
djinni::SharedFuture futureString(strPromise.getFuture()); | ||
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strPromise.setValue(@"foo"); | ||
XCTAssertEqualObjects(futureString.get(), @"foo"); | ||
} | ||
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- (void)testThen | ||
{ | ||
djinni::Promise<int> intPromise; | ||
djinni::SharedFuture<int> futureInt(intPromise.getFuture()); | ||
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auto transformedInt = futureInt.then([](int i) { return 2 * i; }); | ||
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intPromise.setValue(42); | ||
XCTAssertEqual(transformedInt.get(), 84); | ||
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// Also verify multiple consumers and chaining. | ||
auto transformedString = futureInt.then([](int i) { return std::to_string(i); }); | ||
auto futurePlusOneTimesTwo = futureInt.then([](int i) { return i + 1; }).then([](int i) { return 2 * i; }); | ||
auto futureStringLen = transformedString.then([](const std::string& s) { return s.length(); }).toFuture(); | ||
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XCTAssertEqual(transformedString.get(), std::string("42")); | ||
XCTAssertEqual(futurePlusOneTimesTwo.get(), (42 + 1) * 2); | ||
XCTAssertEqual(futureStringLen.get(), 2); | ||
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XCTAssertEqual(futureInt.get(), 42); | ||
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auto voidFuture = transformedString.then([]() {}); | ||
voidFuture.wait(); | ||
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auto intFuture2 = voidFuture.then([]() { return 43; }); | ||
XCTAssertEqual(intFuture2.get(), 43); | ||
} | ||
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@end |