From 8d002659987cd45cb77896fbb173159398138e73 Mon Sep 17 00:00:00 2001
From: MerryMage <MerryMage@users.noreply.github.com>
Date: Sat, 6 Feb 2021 19:13:03 +0000
Subject: [PATCH] ring_buffer: Remove granularity template argument

Non-obvious bug in RingBuffer::Push(std::vector<T>&) when granularity != 1

Just remove it altogether because we do not have a use for granularity != 1
---
 src/common/ring_buffer.h         | 21 ++++++++++-----------
 src/tests/common/ring_buffer.cpp | 10 +++++-----
 2 files changed, 15 insertions(+), 16 deletions(-)

diff --git a/src/common/ring_buffer.h b/src/common/ring_buffer.h
index 138fa0131..4a8d09806 100644
--- a/src/common/ring_buffer.h
+++ b/src/common/ring_buffer.h
@@ -19,15 +19,14 @@ 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>
+template <typename T, std::size_t capacity>
 class RingBuffer {
-    /// A "slot" is made of `granularity` elements of `T`.
-    static constexpr std::size_t slot_size = granularity * sizeof(T);
+    /// 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 / granularity);
+    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);
@@ -47,7 +46,7 @@ public:
         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);
+        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);
 
@@ -74,7 +73,7 @@ public:
         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);
+        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);
 
@@ -84,9 +83,9 @@ public:
     }
 
     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);
+        std::vector<T> out(std::min(max_slots, capacity));
+        const std::size_t count = Pop(out.data(), out.size());
+        out.resize(count);
         return out;
     }
 
@@ -113,7 +112,7 @@ private:
     alignas(128) std::atomic_size_t m_write_index{0};
 #endif
 
-    std::array<T, granularity * capacity> m_data;
+    std::array<T, capacity> m_data;
 };
 
 } // namespace Common
diff --git a/src/tests/common/ring_buffer.cpp b/src/tests/common/ring_buffer.cpp
index 54def22da..903626e4b 100644
--- a/src/tests/common/ring_buffer.cpp
+++ b/src/tests/common/ring_buffer.cpp
@@ -14,7 +14,7 @@
 namespace Common {
 
 TEST_CASE("RingBuffer: Basic Tests", "[common]") {
-    RingBuffer<char, 4, 1> buf;
+    RingBuffer<char, 4> buf;
 
     // Pushing values into a ring buffer with space should succeed.
     for (std::size_t i = 0; i < 4; i++) {
@@ -77,7 +77,7 @@ TEST_CASE("RingBuffer: Basic Tests", "[common]") {
 }
 
 TEST_CASE("RingBuffer: Threaded Test", "[common]") {
-    RingBuffer<char, 4, 2> buf;
+    RingBuffer<char, 8> buf;
     const char seed = 42;
     const std::size_t count = 1000000;
     std::size_t full = 0;
@@ -92,8 +92,8 @@ TEST_CASE("RingBuffer: Threaded Test", "[common]") {
         std::array<char, 2> value = {seed, seed};
         std::size_t i = 0;
         while (i < count) {
-            if (const std::size_t c = buf.Push(&value[0], 1); c > 0) {
-                REQUIRE(c == 1U);
+            if (const std::size_t c = buf.Push(&value[0], 2); c > 0) {
+                REQUIRE(c == 2U);
                 i++;
                 next_value(value);
             } else {
@@ -107,7 +107,7 @@ TEST_CASE("RingBuffer: Threaded Test", "[common]") {
         std::array<char, 2> value = {seed, seed};
         std::size_t i = 0;
         while (i < count) {
-            if (const std::vector<char> v = buf.Pop(1); v.size() > 0) {
+            if (const std::vector<char> v = buf.Pop(2); v.size() > 0) {
                 REQUIRE(v.size() == 2U);
                 REQUIRE(v[0] == value[0]);
                 REQUIRE(v[1] == value[1]);