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// SPDX-License-Identifier: GPL-2.0-or-later
/** \file Pool
* Block allocator optimised for many allocations that are freed all at once.
*/
#ifndef INKSCAPE_UTIL_POOL_H
#define INKSCAPE_UTIL_POOL_H
#include <memory>
#include <vector>
#include <utility>
#include <cstddef>
namespace Inkscape {
namespace Util {
/**
* A Pool is a block allocator with the following characteristics:
*
* - When a block cannot be allocated from the current buffer, a new 50% larger buffer is requested.
* - When all blocks are freed, the largest buffer is retained.
*
* The only difference from std::pmr::monotonic_buffer_resource is the second point.
* Like std::pmr::monotonic_buffer_resource, it is also not thread-safe.
*/
class Pool final
{
public:
Pool() = default;
Pool(Pool const &) = delete;
Pool &operator=(Pool const &) = delete;
Pool(Pool &&other) noexcept { movefrom(other); }
Pool &operator=(Pool &&other) noexcept { movefrom(other); return *this; }
/// Ensure that the next buffer requested has at least the specified size.
void reserve(std::size_t size) { nextsize = std::max(nextsize, size); }
/// Allocate a block of the given size and alignment.
std::byte *allocate(std::size_t size, std::size_t alignment);
/// Convenience function: allocate a block of size and aligment for T.
template<typename T>
T *allocate() { return reinterpret_cast<T*>(allocate(sizeof(T), alignof(T))); }
/// Free all previous allocations, retaining the largest existing buffer for re-use.
void free_all() noexcept;
private:
std::vector<std::unique_ptr<std::byte[]>> buffers;
std::byte *cur = nullptr, *end = nullptr;
std::size_t cursize = 0, nextsize = 2;
void movefrom(Pool &other) noexcept;
void resetblock() noexcept;
};
} // namespace Util
} // namespace Inkscape
#endif // INKSCAPE_UTIL_POOL_H
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