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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include <cstdint>
#include <memory>
namespace mongo {
template <typename DecoratedType>
class DecorationRegistry;
template <typename DecoratedType>
class Decorable;
/**
* An container for decorations.
*/
template <typename DecoratedType>
class DecorationContainer {
DecorationContainer(const DecorationContainer&) = delete;
DecorationContainer& operator=(const DecorationContainer&) = delete;
public:
/**
* Opaque descriptor of a decoration. It is an identifier to a field on the
* DecorationContainer that is private to those modules that have access to the descriptor.
*/
class DecorationDescriptor {
public:
DecorationDescriptor() = default;
private:
friend DecorationContainer;
friend DecorationRegistry<DecoratedType>;
friend Decorable<DecoratedType>;
explicit DecorationDescriptor(size_t index) : _index(index) {}
size_t _index;
};
/**
* Opaque description of a decoration of specified type T. It is an identifier to a field
* on the DecorationContainer that is private to those modules that have access to the
* descriptor.
*/
template <typename T>
class DecorationDescriptorWithType {
public:
DecorationDescriptorWithType() = default;
private:
friend DecorationContainer;
friend DecorationRegistry<DecoratedType>;
friend Decorable<DecoratedType>;
explicit DecorationDescriptorWithType(DecorationDescriptor raw) : _raw(std::move(raw)) {}
DecorationDescriptor _raw;
};
/**
* Constructs a decorable built based on the given "registry."
*
* The registry must stay in scope for the lifetime of the DecorationContainer, and must not
* have any declareDecoration() calls made on it while a DecorationContainer dependent on it
* is in scope.
*/
explicit DecorationContainer(Decorable<DecoratedType>* const decorated,
const DecorationRegistry<DecoratedType>* const registry)
: _registry(registry),
_decorationData(new unsigned char[registry->getDecorationBufferSizeBytes()]) {
// Because the decorations live in the externally allocated storage buffer at
// `_decorationData`, there needs to be a way to get back from a known location within this
// buffer to the type which owns those decorations. We place a pointer to ourselves, a
// "back link" in the front of this storage buffer, as this is the easiest "well known
// location" to compute.
auto const backLink = reinterpret_cast<Decorable<DecoratedType>**>(_decorationData.get());
*backLink = decorated;
_registry->construct(this);
}
/**
* Constructs a copyable decorable built based on the given "registry."
*
* All decorations are copy constructed from provided DecorationContainer.
*/
explicit DecorationContainer(Decorable<DecoratedType>* const decorated,
const DecorationRegistry<DecoratedType>* const registry,
const DecorationContainer& other)
: _registry(registry),
_decorationData(new unsigned char[registry->getDecorationBufferSizeBytes()]) {
// Because the decorations live in the externally allocated storage buffer at
// `_decorationData`, there needs to be a way to get back from a known location within this
// buffer to the type which owns those decorations. We place a pointer to ourselves, a
// "back link" in the front of this storage buffer, as this is the easiest "well known
// location" to compute.
auto const backLink = reinterpret_cast<Decorable<DecoratedType>**>(_decorationData.get());
*backLink = decorated;
_registry->copyConstruct(this, &other);
}
~DecorationContainer() {
_registry->destroy(this);
}
/**
* Gets the decorated value for the given descriptor.
*
* The descriptor must be one returned from this DecorationContainer's associated _registry.
*/
void* getDecoration(DecorationDescriptor descriptor) {
return _decorationData.get() + descriptor._index;
}
/**
* Same as the non-const form above, but returns a const result.
*/
const void* getDecoration(DecorationDescriptor descriptor) const {
return _decorationData.get() + descriptor._index;
}
/**
* Gets the decorated value or the given typed descriptor.
*/
template <typename T>
T& getDecoration(DecorationDescriptorWithType<T> descriptor) {
return *static_cast<T*>(getDecoration(descriptor._raw));
}
/**
* Same as the non-const form above, but returns a const result.
*/
template <typename T>
const T& getDecoration(DecorationDescriptorWithType<T> descriptor) const {
return *static_cast<const T*>(getDecoration(descriptor._raw));
}
private:
const DecorationRegistry<DecoratedType>* const _registry;
const std::unique_ptr<unsigned char[]> _decorationData;
};
} // namespace mongo
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