From 6bfa4fa64306d2fc882282ea147f2b22afd4a9cb Mon Sep 17 00:00:00 2001
From: Silent <zdanio95@gmail.com>
Date: Sat, 31 Aug 2019 20:27:15 +0200
Subject: [PATCH] LogWidget: Use FixedSizeQueue for a log messages buffer

Messages buffer is intended to be of a fixed capacity (MAX_LOG_LINES),
which cannot be achieved by std::queue unless we manually pop() extra elements.
std::queue uses std::deque internally which most likely results in allocations performed continuously.
FixedSizeQueue keeps a single buffer during its entire lifetime, avoiding any allocations except the ones
performed by stored objects.
---
 Source/Core/DolphinQt/Config/LogWidget.cpp | 19 +++++++------------
 Source/Core/DolphinQt/Config/LogWidget.h   |  7 +++++--
 2 files changed, 12 insertions(+), 14 deletions(-)

diff --git a/Source/Core/DolphinQt/Config/LogWidget.cpp b/Source/Core/DolphinQt/Config/LogWidget.cpp
index 743d2b187ea8..d73841f26af0 100644
--- a/Source/Core/DolphinQt/Config/LogWidget.cpp
+++ b/Source/Core/DolphinQt/Config/LogWidget.cpp
@@ -19,8 +19,6 @@
 
 // Delay in ms between calls of UpdateLog()
 constexpr int UPDATE_LOG_DELAY = 100;
-// Maximum number of lines to show in log viewer
-constexpr int MAX_LOG_LINES = 5000;
 // Maximum lines to process at a time
 constexpr size_t MAX_LOG_LINES_TO_UPDATE = 200;
 // Timestamp length
@@ -70,16 +68,13 @@ void LogWidget::UpdateLog()
   std::vector<LogEntry> elements_to_push;
   {
     std::lock_guard lock(m_log_mutex);
-    if (m_log_queue.empty())
+    if (m_log_ring_buffer.empty())
       return;
 
-    elements_to_push.reserve(std::min(MAX_LOG_LINES_TO_UPDATE, m_log_queue.size()));
+    elements_to_push.reserve(std::min(MAX_LOG_LINES_TO_UPDATE, m_log_ring_buffer.size()));
 
-    for (size_t i = 0; !m_log_queue.empty() && i < MAX_LOG_LINES_TO_UPDATE; i++)
-    {
-      elements_to_push.push_back(std::move(m_log_queue.front()));
-      m_log_queue.pop();
-    }
+    for (size_t i = 0; !m_log_ring_buffer.empty() && i < MAX_LOG_LINES_TO_UPDATE; i++)
+      elements_to_push.push_back(std::move(m_log_ring_buffer.pop_front()));
   }
 
   for (auto& line : elements_to_push)
@@ -168,7 +163,7 @@ void LogWidget::ConnectWidgets()
 {
   connect(m_log_clear, &QPushButton::clicked, [this] {
     m_log_text->clear();
-    m_log_queue = {};
+    m_log_ring_buffer.clear();
   });
   connect(m_log_wrap, &QCheckBox::toggled, this, &LogWidget::SaveSettings);
   connect(m_log_font, static_cast<void (QComboBox::*)(int)>(&QComboBox::currentIndexChanged), this,
@@ -219,8 +214,8 @@ void LogWidget::Log(LogTypes::LOG_LEVELS level, const char* text)
     text_length--;
 
   std::lock_guard lock(m_log_mutex);
-  m_log_queue.emplace(std::piecewise_construct, std::forward_as_tuple(text, text_length),
-                      std::forward_as_tuple(level));
+  m_log_ring_buffer.emplace(std::piecewise_construct, std::forward_as_tuple(text, text_length),
+                            std::forward_as_tuple(level));
 }
 
 void LogWidget::closeEvent(QCloseEvent*)
diff --git a/Source/Core/DolphinQt/Config/LogWidget.h b/Source/Core/DolphinQt/Config/LogWidget.h
index 9c7694b2739d..a56bd3df4b43 100644
--- a/Source/Core/DolphinQt/Config/LogWidget.h
+++ b/Source/Core/DolphinQt/Config/LogWidget.h
@@ -7,9 +7,9 @@
 #include <QDockWidget>
 
 #include <mutex>
-#include <queue>
 #include <string>
 
+#include "Common/FixedSizeQueue.h"
 #include "Common/Logging/LogManager.h"
 
 class QCheckBox;
@@ -49,6 +49,9 @@ class LogWidget final : public QDockWidget, LogListener
 
   using LogEntry = std::pair<std::string, LogTypes::LOG_LEVELS>;
 
+  // Maximum number of lines to show in log viewer
+  static constexpr int MAX_LOG_LINES = 5000;
+
   std::mutex m_log_mutex;
-  std::queue<LogEntry> m_log_queue;
+  FixedSizeQueue<LogEntry, MAX_LOG_LINES> m_log_ring_buffer;
 };