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// Copyright 2021 gRPC authors.
//
// 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.
#ifndef GRPC_SRC_CORE_LIB_PROMISE_CONTEXT_H
#define GRPC_SRC_CORE_LIB_PROMISE_CONTEXT_H
#include <grpc/support/port_platform.h>
#include <type_traits>
#include <utility>
#include <grpc/support/log.h>
namespace grpc_core {
// To avoid accidentally creating context types, we require an explicit
// specialization of this template per context type. The specialization need
// not contain any members, only exist.
// The reason for avoiding this is that context types each use a thread local.
template <typename T>
struct ContextType; // IWYU pragma: keep
namespace promise_detail {
template <typename T>
class Context : public ContextType<T> {
public:
explicit Context(T* p) : old_(current_) { current_ = p; }
~Context() { current_ = old_; }
Context(const Context&) = delete;
Context& operator=(const Context&) = delete;
static T* get() { return current_; }
private:
T* const old_;
static thread_local T* current_;
};
template <typename T>
thread_local T* Context<T>::current_;
template <typename T, typename F>
class WithContext {
public:
WithContext(F f, T* context) : context_(context), f_(std::move(f)) {}
decltype(std::declval<F>()()) operator()() {
Context<T> ctx(context_);
return f_();
}
private:
T* context_;
F f_;
};
} // namespace promise_detail
// Return true if a context of type T is currently active.
template <typename T>
bool HasContext() {
return promise_detail::Context<T>::get() != nullptr;
}
// Retrieve the current value of a context, or abort if the value is unset.
template <typename T>
T* GetContext() {
auto* p = promise_detail::Context<T>::get();
GPR_ASSERT(p != nullptr);
return p;
}
// Given a promise and a context, return a promise that has that context set.
template <typename T, typename F>
promise_detail::WithContext<T, F> WithContext(F f, T* context) {
return promise_detail::WithContext<T, F>(std::move(f), context);
}
} // namespace grpc_core
#endif // GRPC_SRC_CORE_LIB_PROMISE_CONTEXT_H
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