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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 <deque>
#include <memory>
#include "mongo/stdx/mutex.h"
#include "mongo/util/concepts.h"
namespace mongo {
/**
* Simple generator-type iterator
*
* This Iterator caches/obscures the underlying data type to allow subclasses to wrap its more()
* and next() functions.
*/
template <typename DataT>
class RegistryListIterator {
public:
using DataType = DataT;
using ElementType = typename DataT::value_type;
explicit RegistryListIterator(DataT data) : _data{std::move(data)} {}
virtual ~RegistryListIterator() = default;
/**
* Return the next element and advance the iterator
*/
auto next() {
if (!more()) {
return ElementType();
}
return _data[_index++];
}
/**
* Return true if there are more elements available
*/
virtual bool more() const {
return _index < _data.size();
}
private:
DataType _data;
size_t _index = 0;
};
/**
* A synchronized add-only list of elements
*
* A RegistryList is intended to allow concurrent iteration, insertion, and access with minimal
* amounts of resource contention. If each element in the list is a pointer or index, the overhead
* of "deactivated" elements is minimal.
*
* This class does no lifetime management for its elements besides construction and destruction. If
* you use it to store pointers, the pointed-to memory should be immortal.
*/
TEMPLATE(typename ElementT)
REQUIRES(std::is_default_constructible_v<ElementT>)
class RegistryList {
public:
using ElementType = ElementT;
using DataType = std::deque<ElementT>;
using Iterator = RegistryListIterator<DataType>;
virtual ~RegistryList() = default;
/**
* Add an element to the list
*
* @returns The index of the new pointer element
*/
size_t add(ElementType ptr) {
stdx::lock_guard lk(_m);
_data.emplace_back(std::move(ptr));
return _data.size() - 1;
}
/**
* Returns an element at the given index within the list
*/
ElementType at(size_t index) const {
stdx::lock_guard lk(_m);
if (index >= _data.size()) {
// If index is past our synchronized end on the deque, then indexing it will be UB.
return ElementType();
}
return _data[index];
}
/**
* Return the total number of elements in this list
*/
size_t size() const {
stdx::lock_guard lk(_m);
return _data.size();
}
/**
* Return a copy of the underlying data structure
*/
DataType data() const {
stdx::lock_guard lk(_m);
return _data;
}
/**
* Return an iterator for this list
*
* This iterator copies the state of the list at the time of capture. If additional elements are
* added after this function is invoked, they will not be visible via the Iterator.
*/
auto iter() const {
return Iterator(data());
}
private:
mutable stdx::mutex _m; // NOLINT
DataType _data;
};
/**
* Wrap the basic RegistryList concept to handle weak_ptrs
*/
TEMPLATE(typename T)
REQUIRES(std::is_constructible_v<std::weak_ptr<T>>)
class WeakPtrRegistryList : public RegistryList<std::weak_ptr<T>> {
public:
using ElementType = std::weak_ptr<T>;
using BaseList = RegistryList<ElementType>;
using DataType = typename BaseList::DataType;
class Iterator final : public BaseList::Iterator {
public:
using BaseList::Iterator::Iterator;
auto next() {
return BaseList::Iterator::next().lock();
}
};
virtual ~WeakPtrRegistryList() = default;
auto add(const std::shared_ptr<T>& ptr) {
return BaseList::add(std::weak_ptr<T>(ptr));
}
auto at(size_t index) const {
return BaseList::at(index).lock();
}
auto iter() const {
return Iterator(BaseList::data());
}
};
} // namespace mongo
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