From 112351d557a41ed214eeef3a94ad0b7644466fbc Mon Sep 17 00:00:00 2001
From: MerryMage <MerryMage@users.noreply.github.com>
Date: Sat, 8 Sep 2018 14:28:39 +0100
Subject: [PATCH] common: Implement a ring buffer
---
src/common/CMakeLists.txt | 1 +
src/common/ring_buffer.h | 111 ++++++++++++++++++++++++++
src/tests/CMakeLists.txt | 1 +
src/tests/common/ring_buffer.cpp | 130 +++++++++++++++++++++++++++++++
4 files changed, 243 insertions(+)
create mode 100644 src/common/ring_buffer.h
create mode 100644 src/tests/common/ring_buffer.cpp
diff --git a/src/common/CMakeLists.txt b/src/common/CMakeLists.txt
index f41946cc6..6a3f1fe08 100644
--- a/src/common/CMakeLists.txt
+++ b/src/common/CMakeLists.txt
@@ -71,6 +71,7 @@ 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..30d934a38
--- /dev/null
+++ b/src/common/ring_buffer.h
@@ -0,0 +1,111 @@
+// Copyright 2018 yuzu emulator team
+// 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, size_t capacity, size_t granularity = 1>
+class RingBuffer {
+ /// A "slot" is made of `granularity` elements of `T`.
+ static constexpr 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<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<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
+ size_t Push(const void* new_slots, size_t slot_count) {
+ const size_t write_index = m_write_index.load();
+ const size_t slots_free = capacity + m_read_index.load() - write_index;
+ const size_t push_count = std::min(slot_count, slots_free);
+
+ const size_t pos = write_index % capacity;
+ const size_t first_copy = std::min(capacity - pos, push_count);
+ const 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;
+ }
+
+ 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
+ size_t Pop(void* output, size_t max_slots = ~size_t(0)) {
+ const size_t read_index = m_read_index.load();
+ const size_t slots_filled = m_write_index.load() - read_index;
+ const size_t pop_count = std::min(slots_filled, max_slots);
+
+ const size_t pos = read_index % capacity;
+ const size_t first_copy = std::min(capacity - pos, pop_count);
+ const 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(size_t max_slots = ~size_t(0)) {
+ std::vector<T> out(std::min(max_slots, capacity) * granularity);
+ const size_t count = Pop(out.data(), out.size() / granularity);
+ out.resize(count * granularity);
+ return out;
+ }
+
+ /// @returns Number of slots used
+ size_t Size() const {
+ return m_write_index.load() - m_read_index.load();
+ }
+
+ /// @returns Maximum size of ring buffer
+ constexpr 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<size_t> m_read_index{0};
+ alignas(128) std::atomic<size_t> m_write_index{0};
+
+ std::array<T, granularity * capacity> m_data;
+};
+
+} // namespace Common
diff --git a/src/tests/CMakeLists.txt b/src/tests/CMakeLists.txt
index 4d74bb395..4e75a72ec 100644
--- a/src/tests/CMakeLists.txt
+++ b/src/tests/CMakeLists.txt
@@ -1,5 +1,6 @@
add_executable(tests
common/param_package.cpp
+ common/ring_buffer.cpp
core/arm/arm_test_common.cpp
core/arm/arm_test_common.h
core/core_timing.cpp
diff --git a/src/tests/common/ring_buffer.cpp b/src/tests/common/ring_buffer.cpp
new file mode 100644
index 000000000..f3fe57839
--- /dev/null
+++ b/src/tests/common/ring_buffer.cpp
@@ -0,0 +1,130 @@
+// Copyright 2018 yuzu emulator team
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include <algorithm>
+#include <array>
+#include <cstddef>
+#include <numeric>
+#include <thread>
+#include <vector>
+#include <catch2/catch.hpp>
+#include "common/ring_buffer.h"
+
+namespace Common {
+
+TEST_CASE("RingBuffer: Basic Tests", "[common]") {
+ RingBuffer<char, 4, 1> buf;
+
+ // Pushing values into a ring buffer with space should succeed.
+ for (size_t i = 0; i < 4; i++) {
+ const char elem = static_cast<char>(i);
+ const size_t count = buf.Push(&elem, 1);
+ REQUIRE(count == 1);
+ }
+
+ REQUIRE(buf.Size() == 4);
+
+ // Pushing values into a full ring buffer should fail.
+ {
+ const char elem = static_cast<char>(42);
+ const size_t count = buf.Push(&elem, 1);
+ REQUIRE(count == 0);
+ }
+
+ REQUIRE(buf.Size() == 4);
+
+ // Popping multiple values from a ring buffer with values should succeed.
+ {
+ const std::vector<char> popped = buf.Pop(2);
+ REQUIRE(popped.size() == 2);
+ REQUIRE(popped[0] == 0);
+ REQUIRE(popped[1] == 1);
+ }
+
+ REQUIRE(buf.Size() == 2);
+
+ // Popping a single value from a ring buffer with values should succeed.
+ {
+ const std::vector<char> popped = buf.Pop(1);
+ REQUIRE(popped.size() == 1);
+ REQUIRE(popped[0] == 2);
+ }
+
+ REQUIRE(buf.Size() == 1);
+
+ // Pushing more values than space available should partially suceed.
+ {
+ std::vector<char> to_push(6);
+ std::iota(to_push.begin(), to_push.end(), 88);
+ const size_t count = buf.Push(to_push);
+ REQUIRE(count == 3);
+ }
+
+ REQUIRE(buf.Size() == 4);
+
+ // Doing an unlimited pop should pop all values.
+ {
+ const std::vector<char> popped = buf.Pop();
+ REQUIRE(popped.size() == 4);
+ REQUIRE(popped[0] == 3);
+ REQUIRE(popped[1] == 88);
+ REQUIRE(popped[2] == 89);
+ REQUIRE(popped[3] == 90);
+ }
+
+ REQUIRE(buf.Size() == 0);
+}
+
+TEST_CASE("RingBuffer: Threaded Test", "[common]") {
+ RingBuffer<char, 4, 2> buf;
+ const char seed = 42;
+ const size_t count = 1000000;
+ size_t full = 0;
+ size_t empty = 0;
+
+ const auto next_value = [](std::array<char, 2>& value) {
+ value[0] += 1;
+ value[1] += 2;
+ };
+
+ std::thread producer{[&] {
+ std::array<char, 2> value = {seed, seed};
+ size_t i = 0;
+ while (i < count) {
+ if (const size_t c = buf.Push(&value[0], 1); c > 0) {
+ REQUIRE(c == 1);
+ i++;
+ next_value(value);
+ } else {
+ full++;
+ std::this_thread::yield();
+ }
+ }
+ }};
+
+ std::thread consumer{[&] {
+ std::array<char, 2> value = {seed, seed};
+ size_t i = 0;
+ while (i < count) {
+ if (const std::vector<char> v = buf.Pop(1); v.size() > 0) {
+ REQUIRE(v.size() == 2);
+ REQUIRE(v[0] == value[0]);
+ REQUIRE(v[1] == value[1]);
+ i++;
+ next_value(value);
+ } else {
+ empty++;
+ std::this_thread::yield();
+ }
+ }
+ }};
+
+ producer.join();
+ consumer.join();
+
+ REQUIRE(buf.Size() == 0);
+ printf("RingBuffer: Threaded Test: full: %zu, empty: %zu\n", full, empty);
+}
+
+} // namespace Common