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// SPDX-FileCopyrightText: Copyright 2018 yuzu Emulator Project
// SPDX-License-Identifier: GPL-2.0-or-later
#pragma once
#include <algorithm>
#include <array>
#include <atomic>
#include <cstddef>
#include <cstring>
#include <new>
#include <span>
#include <type_traits>
#include <vector>
namespace Common {
/// SPSC ring buffer
/// @tparam T Element type
/// @tparam capacity Number of slots in ring buffer
template <typename T, std::size_t capacity>
class RingBuffer {
/// A "slot" is made of a single `T`.
static constexpr std::size_t slot_size = sizeof(T);
// T must be safely memcpy-able and have a trivial default constructor.
static_assert(std::is_trivial_v<T>);
// Ensure capacity is sensible.
static_assert(capacity < std::numeric_limits<std::size_t>::max() / 2);
static_assert((capacity & (capacity - 1)) == 0, "capacity must be a power of two");
// Ensure lock-free.
static_assert(std::atomic_size_t::is_always_lock_free);
public:
/// Pushes slots into the ring buffer
/// @param new_slots Pointer to the slots to push
/// @param slot_count Number of slots to push
/// @returns The number of slots actually pushed
std::size_t Push(const void* new_slots, std::size_t slot_count) {
const std::size_t write_index = m_write_index.load();
const std::size_t slots_free = capacity + m_read_index.load() - write_index;
const std::size_t push_count = std::min(slot_count, slots_free);
const std::size_t pos = write_index % capacity;
const std::size_t first_copy = std::min(capacity - pos, push_count);
const std::size_t second_copy = push_count - first_copy;
const char* in = static_cast<const char*>(new_slots);
std::memcpy(m_data.data() + pos, in, first_copy * slot_size);
in += first_copy * slot_size;
std::memcpy(m_data.data(), in, second_copy * slot_size);
m_write_index.store(write_index + push_count);
return push_count;
}
std::size_t Push(std::span<const T> input) {
return Push(input.data(), input.size());
}
/// Pops slots from the ring buffer
/// @param output Where to store the popped slots
/// @param max_slots Maximum number of slots to pop
/// @returns The number of slots actually popped
std::size_t Pop(void* output, std::size_t max_slots = ~std::size_t(0)) {
const std::size_t read_index = m_read_index.load();
const std::size_t slots_filled = m_write_index.load() - read_index;
const std::size_t pop_count = std::min(slots_filled, max_slots);
const std::size_t pos = read_index % capacity;
const std::size_t first_copy = std::min(capacity - pos, pop_count);
const std::size_t second_copy = pop_count - first_copy;
char* out = static_cast<char*>(output);
std::memcpy(out, m_data.data() + pos, first_copy * slot_size);
out += first_copy * slot_size;
std::memcpy(out, m_data.data(), second_copy * slot_size);
m_read_index.store(read_index + pop_count);
return pop_count;
}
std::vector<T> Pop(std::size_t max_slots = ~std::size_t(0)) {
std::vector<T> out(std::min(max_slots, capacity));
const std::size_t count = Pop(out.data(), out.size());
out.resize(count);
return out;
}
/// @returns Number of slots used
[[nodiscard]] std::size_t Size() const {
return m_write_index.load() - m_read_index.load();
}
/// @returns Maximum size of ring buffer
[[nodiscard]] constexpr std::size_t Capacity() const {
return capacity;
}
private:
// It is important to align the below variables for performance reasons:
// Having them on the same cache-line would result in false-sharing between them.
// TODO: Remove this ifdef whenever clang and GCC support
// std::hardware_destructive_interference_size.
#ifdef __cpp_lib_hardware_interference_size
alignas(std::hardware_destructive_interference_size) std::atomic_size_t m_read_index{0};
alignas(std::hardware_destructive_interference_size) std::atomic_size_t m_write_index{0};
#else
alignas(128) std::atomic_size_t m_read_index{0};
alignas(128) std::atomic_size_t m_write_index{0};
#endif
std::array<T, capacity> m_data;
};
} // namespace Common
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