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/* Copyright (c) 2020, 2025, Oracle and/or its affiliates.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License, version 2.0,
as published by the Free Software Foundation.
This program is designed to work with certain software (including
but not limited to OpenSSL) that is licensed under separate terms,
as designated in a particular file or component or in included license
documentation. The authors of MySQL hereby grant you an additional
permission to link the program and your derivative works with the
separately licensed software that they have either included with
the program or referenced in the documentation.
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
GNU General Public License, version 2.0, for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */
#ifndef CONTAINER_ARRAY_ATOMICS_INDEX_PADDING
#define CONTAINER_ARRAY_ATOMICS_INDEX_PADDING
#include <algorithm>
#include <atomic>
#include <cmath>
#include <map>
#include <memory>
#include <sstream>
#include <thread>
#include <tuple>
#include "sql/memory/aligned_atomic.h" // memory::minimum_cacheline_for
namespace container {
/**
Indexing provider that pads each of the array elements to the size of the
CPU cache line, in order to avoid false sharing and cache misses.
In terms of the array size, this indexing provider will use force the use
of more memory than the needed to store the array elements of type
`T`. If the array is of size `n`, then instead of the allocated memory
being `n * sizeof(std::atomic<T>)`, it will be of size `n *
cache_line_size`. Since, typically, in modern systems, the cache line
size is 64 or 128 bytes, that would be an increase in the allocated
memory.
This class translates element-to-byte indexing as if each element is
aligned with the size of the CPU cache line. The CPU cache line size is
calculated at runtime.
*/
template <typename T>
class Padded_indexing {
public:
using type = std::atomic<T>;
/**
Constructor for the class that takes the maximum allowed number of
elements in the array.
*/
Padded_indexing(size_t max_size);
/**
Class destructor.
*/
virtual ~Padded_indexing() = default;
/**
The size of the array.
@return the size of the array
*/
size_t size() const;
/**
Translates the element index to the byte position in the array.
@param index the element index to be translated.
@return the byte position in the byte array.
*/
size_t translate(size_t index) const;
/**
The array element size, in bytes.
@return The array element size, in bytes.
*/
static size_t element_size();
private:
/** The size of the array */
size_t m_size{0};
/** The size of the CPU cache line */
size_t m_cacheline_size{0};
};
} // namespace container
template <typename T>
container::Padded_indexing<T>::Padded_indexing(size_t size)
: m_size{size},
m_cacheline_size{memory::minimum_cacheline_for<Padded_indexing::type>()} {
}
template <typename T>
size_t container::Padded_indexing<T>::size() const {
return this->m_size;
}
template <typename T>
size_t container::Padded_indexing<T>::translate(size_t index) const {
return index * this->m_cacheline_size;
}
template <typename T>
size_t container::Padded_indexing<T>::element_size() {
return memory::minimum_cacheline_for<Padded_indexing::type>();
}
#endif // CONTAINER_ARRAY_ATOMICS_INDEX_PADDING
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