[Lldb-commits] [lldb] [lldb] Optimize statusline redrawing on terminal size change (PR #146435)

[via lldb-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-lldb

Author: Jonas Devlieghere (JDevlieghere)

<details>
<summary>Changes</summary>

Avoid some of the work to disable/enable the statusline when the terminal dimensions change.

---
Full diff: https://github.com/llvm/llvm-project/pull/146435.diff


2 Files Affected:

- (modified) lldb/include/lldb/Core/Statusline.h (-3) 
- (modified) lldb/source/Core/Statusline.cpp (+19-10) 


``````````diff
diff --git a/lldb/include/lldb/Core/Statusline.h b/lldb/include/lldb/Core/Statusline.h
index 521b9f2526f6b..98c4f0681d61e 100644
--- a/lldb/include/lldb/Core/Statusline.h
+++ b/lldb/include/lldb/Core/Statusline.h
@@ -36,9 +36,6 @@ class Statusline {
   /// Draw the statusline with the given text.
   void Draw(std::string msg);
 
-  /// Update terminal dimensions.
-  void UpdateTerminalProperties();
-
   enum ScrollWindowMode {
     EnableStatusline,
     DisableStatusline,
diff --git a/lldb/source/Core/Statusline.cpp b/lldb/source/Core/Statusline.cpp
index 8ec57c9fa5bac..327ba0ea62465 100644
--- a/lldb/source/Core/Statusline.cpp
+++ b/lldb/source/Core/Statusline.cpp
@@ -41,10 +41,26 @@ Statusline::Statusline(Debugger &debugger)
 Statusline::~Statusline() { Disable(); }
 
 void Statusline::TerminalSizeChanged() {
-  UpdateTerminalProperties();
+  const uint64_t terminal_width = m_debugger.GetTerminalWidth();
+  const uint64_t terminal_height = m_debugger.GetTerminalHeight();
+
+  // Remember whether the terminal height changed.
+  const bool terminal_height_changed = terminal_height != m_terminal_height;
+
+  // Avoid clearing the old statusline if it's not visible (i.e. when the
+  // terminal height decreases), unless the width changed and the old statusline
+  // wrapped.
+  if (terminal_height > m_terminal_height || terminal_width < m_terminal_width)
+    UpdateScrollWindow(DisableStatusline);
+
+  // Update the terminal dimensions.
+  m_terminal_width = terminal_width;
+  m_terminal_height = terminal_height;
+
+  // Update the scroll window if the terminal height changed.
+  if (terminal_height_changed)
+    UpdateScrollWindow(EnableStatusline);
 
-  // This definitely isn't signal safe, but the best we can do, until we
-  // have proper signal-catching thread.
   Redraw(/*update=*/false);
 }
 
@@ -85,13 +101,6 @@ void Statusline::Draw(std::string str) {
   locked_stream << ANSI_RESTORE_CURSOR;
 }
 
-void Statusline::UpdateTerminalProperties() {
-  UpdateScrollWindow(DisableStatusline);
-  m_terminal_width = m_debugger.GetTerminalWidth();
-  m_terminal_height = m_debugger.GetTerminalHeight();
-  UpdateScrollWindow(EnableStatusline);
-}
-
 void Statusline::UpdateScrollWindow(ScrollWindowMode mode) {
   assert(m_terminal_width != 0 && m_terminal_height != 0);
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/146435