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/* SPDX-License-Identifier: GPL-2.0-or-later */
/** \file
* \ingroup bli
*
* A `blender::Pool` allows fast allocation and deallocation of many elements of the same type.
*
* It is compatible with types that are not movable.
*
* Freed elements memory will be reused by next allocations.
* Elements are allocated in chunks to reduce memory fragmentation and avoid reallocation.
*/
#pragma once
#include "BLI_stack.hh"
#include "BLI_utility_mixins.hh"
#include "BLI_vector.hh"
namespace blender {
template<typename T, int64_t ChunkLen = 64> class Pool : NonCopyable {
private:
using Chunk = TypedBuffer<T, ChunkLen>;
/** Allocated item buffer. */
Vector<std::unique_ptr<Chunk>> values_;
/** List of freed elements to be use for the next allocations. A Stack is best here to avoid
* overhead when growing the free list. It also offers better cache performance than a queue
* since last added entries will be reused first. */
Stack<T *, 0> free_list_;
public:
~Pool()
{
/* All elements need to be freed before freeing the pool. */
BLI_assert(this->size() == 0);
}
/**
* Construct an object inside this pool's memory.
*/
template<typename... ForwardT> T &construct(ForwardT &&...value)
{
if (free_list_.is_empty()) {
values_.append(std::make_unique<Chunk>());
T *chunk_start = values_.last()->ptr();
for (auto i : IndexRange(ChunkLen)) {
free_list_.push(chunk_start + i);
}
}
T *ptr = free_list_.pop();
new (ptr) T(std::forward<ForwardT>(value)...);
return *ptr;
}
/**
* Destroy the given element inside this memory pool. Memory will be reused by next element
* construction. This invokes undefined behavior if the item is not from this pool.
*/
void destruct(T &value)
{
value.~T();
free_list_.push(&value);
}
/**
* Return the number of constructed elements in this pool.
*/
int64_t size() const
{
return values_.size() * ChunkLen - free_list_.size();
}
/**
* Returns true when the pool contains no elements, otherwise false.
*/
bool is_empty() const
{
return this->size() == 0;
}
};
} // namespace blender
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