common: Implement a ring buffer

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

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

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

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