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82 lines
2.2 KiB
82 lines
2.2 KiB
// 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_CONTEXT_H |
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#define GRPC_CORE_LIB_PROMISE_CONTEXT_H |
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#include <grpc/support/port_platform.h> |
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#include <utility> |
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namespace grpc_core { |
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// To avoid accidentally creating context types, we require an explicit |
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// specialization of this template per context type. The specialization need |
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// not contain any members, only exist. |
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// The reason for avoiding this is that context types each use a thread local. |
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template <typename T> |
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struct ContextType; // IWYU pragma: keep |
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namespace promise_detail { |
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template <typename T> |
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class Context : public ContextType<T> { |
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public: |
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explicit Context(T* p) : old_(current_) { current_ = p; } |
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~Context() { current_ = old_; } |
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Context(const Context&) = delete; |
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Context& operator=(const Context&) = delete; |
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static T* get() { return current_; } |
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private: |
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T* const old_; |
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static thread_local T* current_; |
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}; |
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template <typename T> |
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thread_local T* Context<T>::current_; |
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template <typename T, typename F> |
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class WithContext { |
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public: |
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WithContext(F f, T* context) : context_(context), f_(std::move(f)) {} |
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decltype(std::declval<F>()()) operator()() { |
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Context<T> ctx(context_); |
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return f_(); |
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} |
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private: |
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T* context_; |
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F f_; |
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}; |
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} // namespace promise_detail |
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// Retrieve the current value of a context. |
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template <typename T> |
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T* GetContext() { |
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return promise_detail::Context<T>::get(); |
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} |
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// Given a promise and a context, return a promise that has that context set. |
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template <typename T, typename F> |
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promise_detail::WithContext<T, F> WithContext(F f, T* context) { |
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return promise_detail::WithContext<T, F>(std::move(f), context); |
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} |
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} // namespace grpc_core |
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#endif // GRPC_CORE_LIB_PROMISE_CONTEXT_H
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