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Craig Tiller
3 years ago
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// Copyright 2021 gRPC authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#ifndef GRPC_CORE_LIB_PROMISE_ARENA_PROMISE_H |
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#define GRPC_CORE_LIB_PROMISE_ARENA_PROMISE_H |
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#include <grpc/support/port_platform.h> |
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#include <grpc/support/log.h> |
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#include "src/core/lib/gprpp/arena.h" |
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#include "src/core/lib/promise/poll.h" |
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namespace grpc_core { |
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namespace arena_promise_detail { |
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// Type erased promise stored in the arena.
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template <typename T> |
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class ImplInterface { |
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public: |
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// Poll the promise, once.
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virtual Poll<T> PollOnce() = 0; |
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// Destroy the underlying callable object if there is one.
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// Since we don't delete (the arena owns the memory) but we may need to call a
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// destructor, we expose this for when the ArenaPromise object is destroyed.
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virtual void Destroy() = 0; |
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protected: |
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~ImplInterface() = default; |
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}; |
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// Implementation of ImplInterface for an empty object.
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// Used when an empty ArenaPromise is created, or when the ArenaPromise is moved
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// from. Since in either case these objects should not be polled, we simply
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// crash if it is.
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template <typename T> |
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class NullImpl final : public ImplInterface<T> { |
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public: |
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Poll<T> PollOnce() override { |
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abort(); |
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GPR_UNREACHABLE_CODE(return Pending{}); |
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} |
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void Destroy() override {} |
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static ImplInterface<T>* Get() { |
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static NullImpl<T> instance; |
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return &instance; |
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} |
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private: |
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~NullImpl() = default; |
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}; |
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// Implementation of ImplInterface for a callable object.
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template <typename T, typename Callable> |
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class CallableImpl final : public ImplInterface<T> { |
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public: |
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explicit CallableImpl(Callable&& callable) : callable_(std::move(callable)) {} |
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// Forward polls to the callable object.
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Poll<T> PollOnce() override { return callable_(); } |
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// Destroy destructs the callable object.
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void Destroy() override { this->~CallableImpl(); } |
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private: |
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// Should only be called by Destroy().
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~CallableImpl() = default; |
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Callable callable_; |
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}; |
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// If a callable object is empty we can substitute any instance of that callable
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// for the one we call (for how could we tell the difference)?
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// Since this corresponds to a lambda with no fields, and we expect these to be
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// reasonably common, we can elide the arena allocation entirely and simply poll
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// a global shared instance.
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// (this comes up often when the promise only accesses context data from the
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// containing activity).
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template <typename T, typename Callable> |
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class SharedImpl final : public ImplInterface<T> { |
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public: |
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// Call the callable. Since it's empty it can't access any member variables,
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// and as such we can choose any address for the object.
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Poll<T> PollOnce() override { return (*static_cast<Callable*>(nullptr))(); } |
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// Nothing to destroy.
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void Destroy() override {} |
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// Return a pointer to the shared instance - these are singletons, and are
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// needed just to get the vtable in place.
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static SharedImpl* Get() { |
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static SharedImpl impl; |
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return &impl; |
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} |
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private: |
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SharedImpl() = default; |
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~SharedImpl() = default; |
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}; |
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// Redirector type: given a callable type, expose a Make() function that creates
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// the appropriate underlying implementation.
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template <typename T, typename Callable, typename Ignored = void> |
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struct ChooseImplForCallable; |
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template <typename T, typename Callable> |
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struct ChooseImplForCallable< |
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T, Callable, absl::enable_if_t<!std::is_empty<Callable>::value>> { |
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static ImplInterface<T>* Make(Arena* arena, Callable&& callable) { |
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return arena->template New<CallableImpl<T, Callable>>( |
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std::forward<Callable>(callable)); |
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} |
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}; |
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template <typename T, typename Callable> |
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struct ChooseImplForCallable< |
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T, Callable, absl::enable_if_t<std::is_empty<Callable>::value>> { |
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static ImplInterface<T>* Make(Arena*, Callable&&) { |
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return SharedImpl<T, Callable>::Get(); |
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} |
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}; |
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// Wrap ChooseImplForCallable with a friend approachable syntax.
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template <typename T, typename Callable> |
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ImplInterface<T>* MakeImplForCallable(Arena* arena, Callable&& callable) { |
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return ChooseImplForCallable<T, Callable>::Make( |
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arena, std::forward<Callable>(callable)); |
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} |
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} // namespace arena_promise_detail
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// A promise for which the state memory is allocated from an arena.
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template <typename T> |
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class ArenaPromise { |
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public: |
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// Construct an empty, uncallable, invalid ArenaPromise.
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ArenaPromise() = default; |
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// Construct an ArenaPromise that will call the given callable when polled.
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template <typename Callable> |
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ArenaPromise(Arena* arena, Callable&& callable) |
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: impl_(arena_promise_detail::MakeImplForCallable<T>( |
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arena, std::forward<Callable>(callable))) {} |
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// ArenaPromise is not copyable.
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ArenaPromise(const ArenaPromise&) = delete; |
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ArenaPromise& operator=(const ArenaPromise&) = delete; |
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// ArenaPromise is movable.
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ArenaPromise(ArenaPromise&& other) noexcept : impl_(other.impl_) { |
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other.impl_ = arena_promise_detail::NullImpl<T>::Get(); |
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} |
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ArenaPromise& operator=(ArenaPromise&& other) noexcept { |
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impl_ = other.impl_; |
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other.impl_ = arena_promise_detail::NullImpl<T>::Get(); |
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return *this; |
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} |
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// Destruction => call Destroy on the underlying impl object.
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~ArenaPromise() { impl_->Destroy(); } |
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// Expose the promise interface: a call operator that returns Poll<T>.
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Poll<T> operator()() { return impl_->PollOnce(); } |
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private: |
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// Underlying impl object.
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arena_promise_detail::ImplInterface<T>* impl_ = |
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arena_promise_detail::NullImpl<T>::Get(); |
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}; |
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} // namespace grpc_core
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#endif /* GRPC_CORE_LIB_PROMISE_ARENA_PROMISE_H */ |
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@ -1,45 +0,0 @@ |
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// Copyright 2021 gRPC authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include "src/core/lib/promise/arena_promise.h" |
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#include <memory> |
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#include <gtest/gtest.h> |
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namespace grpc_core { |
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TEST(ArenaPromiseTest, AllocatedWorks) { |
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auto arena = MakeScopedArena(1024); |
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int x = 42; |
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ArenaPromise<int> p(arena.get(), [x] { return Poll<int>(x); }); |
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EXPECT_EQ(p(), Poll<int>(42)); |
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p = ArenaPromise<int>(arena.get(), [] { return Poll<int>(43); }); |
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EXPECT_EQ(p(), Poll<int>(43)); |
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} |
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TEST(ArenaPromiseTest, DestructionWorks) { |
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auto arena = MakeScopedArena(1024); |
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auto x = std::make_shared<int>(42); |
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auto p = ArenaPromise<int>(arena.get(), [x] { return Poll<int>(*x); }); |
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ArenaPromise<int> q(std::move(p)); |
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EXPECT_EQ(q(), Poll<int>(42)); |
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} |
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} // namespace grpc_core
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int main(int argc, char** argv) { |
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::testing::InitGoogleTest(&argc, argv); |
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return RUN_ALL_TESTS(); |
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} |
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