From a2e22dc17b8f3ff56f5d5dc3aa6ff90284335cd0 Mon Sep 17 00:00:00 2001
From: Paul Licameli <paul.licameli@audacityteam.org>
Date: Sun, 6 Sep 2020 16:27:19 -0400
Subject: [PATCH] TransactionScope for performance also when abandoning redo
 states

---
 src/HistoryWindow.cpp   |  2 +-
 src/ProjectManager.cpp  |  2 +-
 src/UndoManager.cpp     | 27 ++++++++++++---------------
 src/UndoManager.h       |  5 ++++-
 src/menus/FileMenus.cpp |  2 +-
 5 files changed, 19 insertions(+), 19 deletions(-)

diff --git a/src/HistoryWindow.cpp b/src/HistoryWindow.cpp
index e8aeb8891..034c0704c 100644
--- a/src/HistoryWindow.cpp
+++ b/src/HistoryWindow.cpp
@@ -269,7 +269,7 @@ void HistoryDialog::OnDiscard(wxCommandEvent & WXUNUSED(event))
    int i = mLevels->GetValue();
 
    mSelected -= i;
-   mManager->RemoveStates(i);
+   mManager->RemoveStates(0, i);
    ProjectHistory::Get( *mProject ).SetStateTo(mSelected);
 
    while(--i >= 0)
diff --git a/src/ProjectManager.cpp b/src/ProjectManager.cpp
index 8c1b3338b..b9707e0dd 100644
--- a/src/ProjectManager.cpp
+++ b/src/ProjectManager.cpp
@@ -899,7 +899,7 @@ AudacityProject *ProjectManager::OpenProject(
       window.Zoom( window.GetZoomOfToFit() );
       // "Project was recovered" replaces "Create new project" in Undo History.
       auto &undoManager = UndoManager::Get( *pProject );
-      undoManager.RemoveStates(1);
+      undoManager.RemoveStates(0, 1);
    }
 
    return pProject;
diff --git a/src/UndoManager.cpp b/src/UndoManager.cpp
index 35f516532..48a7dc02f 100644
--- a/src/UndoManager.cpp
+++ b/src/UndoManager.cpp
@@ -180,18 +180,20 @@ void UndoManager::RemoveStateAt(int n)
 }
 
 
-void UndoManager::RemoveStates(int num)
+void UndoManager::RemoveStates(size_t begin, size_t end)
 {
    Optional<TransactionScope> pTrans;
    auto pConnection = ConnectionPtr::Get(mProject).mpConnection.get();
    if (pConnection)
       pTrans.emplace(*pConnection, "DiscardingUndoStates");
 
-   for (int i = 0; i < num; i++) {
-      RemoveStateAt(0);
+   for (size_t ii = begin; ii < end; ++ii) {
+      RemoveStateAt(begin);
 
-      current -= 1;
-      saved -= 1;
+      if (current > begin)
+        --current;
+      if (saved > begin)
+        --saved;
    }
 
    if (pTrans)
@@ -200,7 +202,7 @@ void UndoManager::RemoveStates(int num)
 
 void UndoManager::ClearStates()
 {
-   RemoveStates(stack.size());
+   RemoveStates(0, stack.size());
    current = -1;
    saved = -1;
 }
@@ -264,8 +266,6 @@ void UndoManager::PushState(const TrackList * l,
                             const TranslatableString &shortDescription,
                             UndoPush flags)
 {
-   unsigned int i;
-
    if ( (flags & UndoPush::CONSOLIDATE) != UndoPush::NONE &&
        // compare full translations not msgids!
        lastAction.Translation() == longDescription.Translation() &&
@@ -289,10 +289,11 @@ void UndoManager::PushState(const TrackList * l,
 
    mayConsolidate = true;
 
-   i = current + 1;
-   while (i < stack.size()) {
-      RemoveStateAt(i);
+   // Abandon redo states
+   if (saved >= current) {
+      saved = -1;
    }
+   RemoveStates( current + 1, stack.size() );
 
    // Assume tags was duplicated before any changes.
    // Just save a NEW shared_ptr to it.
@@ -304,10 +305,6 @@ void UndoManager::PushState(const TrackList * l,
 
    current++;
 
-   if (saved >= current) {
-      saved = -1;
-   }
-
    lastAction = longDescription;
 
    // wxWidgets will own the event object
diff --git a/src/UndoManager.h b/src/UndoManager.h
index 801a413e4..d580baaac 100644
--- a/src/UndoManager.h
+++ b/src/UndoManager.h
@@ -132,7 +132,10 @@ class AUDACITY_DLL_API UndoManager final
    void ModifyState(const TrackList * l,
                     const SelectedRegion &selectedRegion, const std::shared_ptr<Tags> &tags);
    void ClearStates();
-   void RemoveStates(int num);  // removes the 'num' oldest states
+   void RemoveStates(
+      size_t begin, //!< inclusive start of range
+      size_t end    //!< exclusive end of range
+   );
    unsigned int GetNumStates();
    unsigned int GetCurrentState();
 
diff --git a/src/menus/FileMenus.cpp b/src/menus/FileMenus.cpp
index 1541931b0..32c79e6a1 100644
--- a/src/menus/FileMenus.cpp
+++ b/src/menus/FileMenus.cpp
@@ -235,7 +235,7 @@ void OnCompact(const CommandContext &context)
 
       // Now we can remove all previous states.
       auto numStates = undoManager.GetNumStates();
-      undoManager.RemoveStates(numStates - 1);
+      undoManager.RemoveStates(0, numStates - 1);
 
       // And clear the clipboard
       clipboard.Clear();