From 761ef78408d8682c04197cb3daaa77a2c65ecca3 Mon Sep 17 00:00:00 2001 From: MerryMage <MerryMage@users.noreply.github.com> Date: Sat, 8 Sep 2018 20:42:25 +0100 Subject: [PATCH] common: Implement a ring buffer --- src/common/CMakeLists.txt | 1 + src/common/ring_buffer.h | 111 ++++++++++++++++++++++++++++++++++++++ 2 files changed, 112 insertions(+) create mode 100644 src/common/ring_buffer.h diff --git a/src/common/CMakeLists.txt b/src/common/CMakeLists.txt index dfc0ea0c1..eed86ae0d 100644 --- a/src/common/CMakeLists.txt +++ b/src/common/CMakeLists.txt @@ -72,6 +72,7 @@ add_library(common STATIC param_package.cpp param_package.h quaternion.h + ring_buffer.h scm_rev.cpp scm_rev.h scope_exit.h diff --git a/src/common/ring_buffer.h b/src/common/ring_buffer.h new file mode 100644 index 000000000..f44d9e8d3 --- /dev/null +++ b/src/common/ring_buffer.h @@ -0,0 +1,111 @@ +// Copyright 2018 Citra Emulator Project +// Licensed under GPLv2 or any later version +// Refer to the license.txt file included. + +#pragma once + +#include <algorithm> +#include <array> +#include <atomic> +#include <cstddef> +#include <cstring> +#include <type_traits> +#include <vector> +#include "common/common_types.h" + +namespace Common { + +/// SPSC ring buffer +/// @tparam T Element type +/// @tparam capacity Number of slots in ring buffer +/// @tparam granularity Slot size in terms of number of elements +template <typename T, std::size_t capacity, std::size_t granularity = 1> +class RingBuffer { + /// A "slot" is made of `granularity` elements of `T`. + static constexpr std::size_t slot_size = granularity * 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 / granularity); + static_assert((capacity & (capacity - 1)) == 0, "capacity must be a power of two"); + // Ensure lock-free. + static_assert(std::atomic<std::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 * granularity, 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(const std::vector<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 * granularity, 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) * granularity); + const std::size_t count = Pop(out.data(), out.size() / granularity); + out.resize(count * granularity); + return out; + } + + /// @returns Number of slots used + std::size_t Size() const { + return m_write_index.load() - m_read_index.load(); + } + + /// @returns Maximum size of ring buffer + 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. + alignas(128) std::atomic<std::size_t> m_read_index{0}; + alignas(128) std::atomic<std::size_t> m_write_index{0}; + + std::array<T, granularity * capacity> m_data; +}; + +} // namespace Common