112 lines
4.1 KiB
C++
112 lines
4.1 KiB
C++
// Copyright 2018 Citra Emulator Project
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// Licensed under GPLv2 or any later version
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// Refer to the license.txt file included.
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#pragma once
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#include <algorithm>
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#include <array>
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#include <atomic>
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#include <cstddef>
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#include <cstring>
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#include <type_traits>
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#include <vector>
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#include "common/common_types.h"
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namespace Common {
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/// SPSC ring buffer
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/// @tparam T Element type
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/// @tparam capacity Number of slots in ring buffer
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/// @tparam granularity Slot size in terms of number of elements
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template <typename T, std::size_t capacity, std::size_t granularity = 1>
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class RingBuffer {
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/// A "slot" is made of `granularity` elements of `T`.
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static constexpr std::size_t slot_size = granularity * sizeof(T);
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// T must be safely memcpy-able and have a trivial default constructor.
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static_assert(std::is_trivial_v<T>);
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// Ensure capacity is sensible.
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static_assert(capacity < std::numeric_limits<std::size_t>::max() / 2 / granularity);
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static_assert((capacity & (capacity - 1)) == 0, "capacity must be a power of two");
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// Ensure lock-free.
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static_assert(std::atomic<std::size_t>::is_always_lock_free);
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public:
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/// Pushes slots into the ring buffer
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/// @param new_slots Pointer to the slots to push
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/// @param slot_count Number of slots to push
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/// @returns The number of slots actually pushed
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std::size_t Push(const void* new_slots, std::size_t slot_count) {
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const std::size_t write_index = m_write_index.load();
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const std::size_t slots_free = capacity + m_read_index.load() - write_index;
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const std::size_t push_count = std::min(slot_count, slots_free);
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const std::size_t pos = write_index % capacity;
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const std::size_t first_copy = std::min(capacity - pos, push_count);
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const std::size_t second_copy = push_count - first_copy;
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const char* in = static_cast<const char*>(new_slots);
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std::memcpy(m_data.data() + pos * granularity, in, first_copy * slot_size);
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in += first_copy * slot_size;
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std::memcpy(m_data.data(), in, second_copy * slot_size);
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m_write_index.store(write_index + push_count);
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return push_count;
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}
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std::size_t Push(const std::vector<T>& input) {
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return Push(input.data(), input.size() / granularity);
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}
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/// Pops slots from the ring buffer
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/// @param output Where to store the popped slots
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/// @param max_slots Maximum number of slots to pop
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/// @returns The number of slots actually popped
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std::size_t Pop(void* output, std::size_t max_slots = ~std::size_t(0)) {
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const std::size_t read_index = m_read_index.load();
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const std::size_t slots_filled = m_write_index.load() - read_index;
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const std::size_t pop_count = std::min(slots_filled, max_slots);
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const std::size_t pos = read_index % capacity;
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const std::size_t first_copy = std::min(capacity - pos, pop_count);
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const std::size_t second_copy = pop_count - first_copy;
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char* out = static_cast<char*>(output);
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std::memcpy(out, m_data.data() + pos * granularity, first_copy * slot_size);
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out += first_copy * slot_size;
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std::memcpy(out, m_data.data(), second_copy * slot_size);
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m_read_index.store(read_index + pop_count);
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return pop_count;
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}
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std::vector<T> Pop(std::size_t max_slots = ~std::size_t(0)) {
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std::vector<T> out(std::min(max_slots, capacity) * granularity);
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const std::size_t count = Pop(out.data(), out.size() / granularity);
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out.resize(count * granularity);
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return out;
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}
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/// @returns Number of slots used
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std::size_t Size() const {
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return m_write_index.load() - m_read_index.load();
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}
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/// @returns Maximum size of ring buffer
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constexpr std::size_t Capacity() const {
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return capacity;
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}
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private:
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// It is important to align the below variables for performance reasons:
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// Having them on the same cache-line would result in false-sharing between them.
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alignas(128) std::atomic<std::size_t> m_read_index{0};
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alignas(128) std::atomic<std::size_t> m_write_index{0};
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std::array<T, granularity * capacity> m_data;
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};
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} // namespace Common
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