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/* -*- Mode: c++ -*- */
/***************************************************************************
* memory_heap.h
*
* Sun Jan 19 13:49:56 CET 2020
* Copyright 2020 André Nusser
* andre.nusser@googlemail.com
****************************************************************************/
/*
* This file is part of DrumGizmo.
*
* DrumGizmo is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 3 of the License, or
* (at your option) any later version.
*
* DrumGizmo 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
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with DrumGizmo; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
*/
#pragma once
#include <vector>
// The purpose of this class is to have a heap for objects of a certain type.
// We want to avoid using the general "new"/"delete" memory allocation as this
// is problematic for real-time as well as slow. The underlying container still
// is a vector to handle the case when for some reason we need more memory
// than initially anticipated. Instead of throwing errors and giving up, we can
// then at least allocate new memory and just hope for the best.
//
// The members add, get, remove correspond to new, dereference, delete. Thus, we
// first add an object and this gives us and index. With this index we can then
// retrieve the object until we remove it. As soon as it is removed, you shouldn't
// use the index anymore to retrieve it (similarly, as you shouldn't use a pointer
// after calling delete on it).
template <typename T>
class MemoryHeap
{
public:
using Index = std::size_t;
using Indices = std::vector<Index>;
MemoryHeap() = default;
MemoryHeap(std::size_t size)
{
memory.reserve(size);
free_indices.reserve(size);
}
template <typename... Args>
Index emplace(Args&&... args);
Index add(const T& element);
T& get(Index index);
const T& get(Index index) const;
void remove(Index index);
private:
std::vector<T> memory;
Indices free_indices;
};
template <typename T>
auto MemoryHeap<T>::add(const T& element) -> Index
{
if (free_indices.empty())
{
memory.push_back(element);
return memory.size()-1;
}
auto free_index = free_indices.back();
free_indices.pop_back();
memory[free_index] = element;
return free_index;
}
template <typename T>
template <typename... Args>
auto MemoryHeap<T>::emplace(Args&&... args) -> Index
{
if (free_indices.empty())
{
memory.emplace_back(std::forward<Args>(args)...);
return memory.size()-1;
}
auto free_index = free_indices.back();
free_indices.pop_back();
memory[free_index] = T(std::forward<Args>(args)...);
return free_index;
}
// Note: MemoryHeap never really deletes anything -- it just overwrites, so
// old indices will always return a valid item wrt. memory.
template <typename T>
T& MemoryHeap<T>::get(Index index)
{
assert(index < memory.size());
return memory[index];
}
template <typename T>
const T& MemoryHeap<T>::get(Index index) const
{
assert(index < memory.size());
return memory[index];
}
template <typename T>
void MemoryHeap<T>::remove(Index index)
{
free_indices.push_back(index);
}
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