Terminal: Improve performance for cat /dev/random

Change-Id: Ibc7e09dd9388fd6f06f0bed3ade4e83d05f03c28
Reviewed-by: Cristian Adam <cristian.adam@qt.io>

src/plugins/terminal/scrollback.cpp

@@ -20,7 +20,6 @@ Scrollback::Line::Line(int cols, const VTermScreenCell *cells, VTermState *vts)
         vterm_state_convert_color_to_rgb(vts, &m_cells[i].fg);
         vterm_state_convert_color_to_rgb(vts, &m_cells[i].bg);
     }
-    m_layout = std::make_unique<QTextLayout>();
 }
 
 const VTermScreenCell *Scrollback::Line::cell(int i) const
@@ -31,6 +30,9 @@ const VTermScreenCell *Scrollback::Line::cell(int i) const
 
 const QTextLayout &Scrollback::Line::layout(int version, const QFont &font, qreal lineSpacing) const
 {
+    if (!m_layout)
+        m_layout = std::make_unique<QTextLayout>();
+
     if (m_layoutVersion != version) {
         QString text;
         VTermColor defaultBg;

src/plugins/terminal/scrollback.h

@@ -33,7 +33,7 @@ public:
     private:
         int m_cols;
         std::unique_ptr<VTermScreenCell[]> m_cells;
-        std::unique_ptr<QTextLayout> m_layout;
+        mutable std::unique_ptr<QTextLayout> m_layout;
         mutable int m_layoutVersion{-1};
     };
 

src/plugins/terminal/terminalwidget.cpp

@@ -29,6 +29,8 @@
 #include <QScrollBar>
 #include <QTextLayout>
 
+#include <chrono>
+
 Q_LOGGING_CATEGORY(terminalLog, "qtc.terminal", QtWarningMsg)
 
 using namespace Utils;
@@ -36,6 +38,11 @@ using namespace Utils::Terminal;
 
 namespace Terminal {
 
+using namespace std::chrono_literals;
+
+// Minimum time between two refreshes.
+static const auto minRefreshInterval = 16ms;
+
 TerminalWidget::TerminalWidget(QWidget *parent, const OpenTerminalParameters &openParameters)
     : QAbstractScrollArea(parent)
     , m_vterm(vterm_new(size().height(), size().width()), vterm_free)
@@ -47,6 +54,7 @@ TerminalWidget::TerminalWidget(QWidget *parent, const OpenTerminalParameters &op
     , m_zoomInAction(Tr::tr("Zoom In"))
     , m_zoomOutAction(Tr::tr("Zoom Out"))
     , m_openParameters(openParameters)
+    , m_lastFlush(QDateTime::currentDateTime())
 {
     setupVTerm();
     setupFont();
@@ -66,13 +74,10 @@ TerminalWidget::TerminalWidget(QWidget *parent, const OpenTerminalParameters &op
 
     setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOn);
 
-    m_readDelayTimer.setSingleShot(true);
-    m_readDelayTimer.setInterval(10);
+    m_flushDelayTimer.setSingleShot(true);
+    m_flushDelayTimer.setInterval(minRefreshInterval);
 
-    connect(&m_readDelayTimer, &QTimer::timeout, this, [this] {
-        m_readDelayRestarts = 0;
-        onReadyRead();
-    });
+    connect(&m_flushDelayTimer, &QTimer::timeout, this, [this]() { flushVTerm(true); });
 
     connect(&m_copyAction, &QAction::triggered, this, &TerminalWidget::copyToClipboard);
     connect(&m_pasteAction, &QAction::triggered, this, &TerminalWidget::pasteFromClipboard);
@@ -109,14 +114,8 @@ void TerminalWidget::setupPty()
         m_process->setWorkingDirectory(*m_openParameters.workingDirectory);
     m_process->setEnvironment(env);
 
-    connect(m_process.get(), &QtcProcess::readyReadStandardOutput, this, [this] {
-        if (m_readDelayTimer.isActive())
-            m_readDelayRestarts++;
-
-        if (m_readDelayRestarts > 100)
-            return;
-
-        m_readDelayTimer.start();
+    connect(m_process.get(), &QtcProcess::readyReadStandardOutput, this, [this]() {
+        onReadyRead(false);
     });
 
     connect(m_process.get(), &QtcProcess::done, this, [this] {
@@ -138,7 +137,9 @@ void TerminalWidget::setupPty()
         }
 
         if (m_openParameters.m_exitBehavior == ExitBehavior::Restart) {
-            QMetaObject::invokeMethod(this, [this] {
+            QMetaObject::invokeMethod(
+                this,
+                [this] {
                     m_process.reset();
                     setupPty();
                 },
@@ -411,17 +412,29 @@ void TerminalWidget::clearContents()
     // Fake a scrollback clearing
     QByteArray data{"\x1b[3J"};
     vterm_input_write(m_vterm.get(), data.constData(), data.size());
-    vterm_screen_flush_damage(m_vtermScreen);
 
     // Send Ctrl+L which will clear the screen
     writeToPty(QByteArray("\f"));
 }
 
-void TerminalWidget::onReadyRead()
+void TerminalWidget::onReadyRead(bool forceFlush)
 {
     QByteArray data = m_process->readAllRawStandardOutput();
     vterm_input_write(m_vterm.get(), data.constData(), data.size());
+
+    flushVTerm(forceFlush);
+}
+
+void TerminalWidget::flushVTerm(bool force)
+{
+    if (force || QDateTime::currentDateTime() - m_lastFlush > minRefreshInterval) {
+        m_lastFlush = QDateTime::currentDateTime();
         vterm_screen_flush_damage(m_vtermScreen);
+        return;
+    }
+
+    if (!m_flushDelayTimer.isActive())
+        m_flushDelayTimer.start();
 }
 
 const VTermScreenCell *TerminalWidget::fetchCell(int x, int y) const
@@ -707,7 +720,7 @@ void TerminalWidget::applySizeChange()
         m_process->ptyData().resize(m_vtermSize);
 
     vterm_set_size(m_vterm.get(), m_vtermSize.height(), m_vtermSize.width());
-    vterm_screen_flush_damage(m_vtermScreen);
+    flushVTerm(true);
 }
 
 void TerminalWidget::updateScrollBars()

src/plugins/terminal/terminalwidget.h

@@ -76,7 +76,7 @@ protected:
     bool event(QEvent *event) override;
 
 protected:
-    void onReadyRead();
+    void onReadyRead(bool forceFlush);
     void setupVTerm();
     void setupFont();
     void setupPty();
@@ -110,6 +110,8 @@ protected:
 
     void updateScrollBars();
 
+    void flushVTerm(bool force);
+
 private:
     std::unique_ptr<Utils::QtcProcess> m_process;
 
@@ -151,14 +153,15 @@ private:
     QAction m_zoomInAction;
     QAction m_zoomOutAction;
 
-    QTimer m_readDelayTimer;
-    int m_readDelayRestarts{0};
+    QTimer m_flushDelayTimer;
 
     int m_layoutVersion{0};
 
     std::array<QColor, 18> m_currentColors;
 
     Utils::Terminal::OpenTerminalParameters m_openParameters;
+
+    QDateTime m_lastFlush;
 };
 
 } // namespace Terminal