chromium/third_party/grpc/src/src/core/lib/promise/context.h

// 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> { … };

template <typename T>
thread_local T* Context<T>::current_;

template <typename T, typename F>
class WithContext { … };

}  // namespace promise_detail

// Return true if a context of type T is currently active.
template <typename T>
bool HasContext() { … }

// Retrieve the current value of a context, or abort if the value is unset.
template <typename T>
T* GetContext() { … }

// 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) { … }

}  // namespace grpc_core

#endif  // GRPC_SRC_CORE_LIB_PROMISE_CONTEXT_H