Exception safety in: batch processing

src/BatchCommands.cpp

@@ -328,7 +328,7 @@ wxString BatchCommands::PromptForParamsFor(const wxString & command, const wxStr
 
    wxString res = params;
 
-   EffectManager::Get().SetBatchProcessing(ID, true);
+   auto cleanup = EffectManager::Get().SetBatchProcessing(ID);
 
    if (EffectManager::Get().SetEffectParameters(ID, params))
    {
@@ -338,8 +338,6 @@ wxString BatchCommands::PromptForParamsFor(const wxString & command, const wxStr
       }
    }
 
-   EffectManager::Get().SetBatchProcessing(ID, false);
-
    return res;
 }
 
@@ -606,7 +604,7 @@ bool BatchCommands::ApplyEffectCommand(const PluginID & ID, const wxString & com
 
    bool res = false;
 
-   EffectManager::Get().SetBatchProcessing(ID, true);
+   auto cleanup = EffectManager::Get().SetBatchProcessing(ID);
 
    // transfer the parameters to the effect...
    if (EffectManager::Get().SetEffectParameters(ID, params))
@@ -617,8 +615,6 @@ bool BatchCommands::ApplyEffectCommand(const PluginID & ID, const wxString & com
                                   AudacityProject::OnEffectFlags::kDontRepeatLast);
    }
 
-   EffectManager::Get().SetBatchProcessing(ID, false);
-
    return res;
 }
 
@@ -652,17 +648,15 @@ bool BatchCommands::ApplyCommand(const wxString & command, const wxString & para
 bool BatchCommands::ApplyCommandInBatchMode(const wxString & command, const wxString &params)
 {
    AudacityProject *project = GetActiveProject();
-   bool rc;
 
    // enter batch mode...
    bool prevShowMode = project->GetShowId3Dialog();
+   auto cleanup = finally( [&] {
+      // exit batch mode...
+      project->SetShowId3Dialog(prevShowMode);
+   } );
 
-   rc = ApplyCommand( command, params );
-
-   // exit batch mode...
-   project->SetShowId3Dialog(prevShowMode);
-
-   return rc;
+   return ApplyCommand( command, params );
 }
 
 // ApplyChain returns true on success, false otherwise.
@@ -670,29 +664,31 @@ bool BatchCommands::ApplyCommandInBatchMode(const wxString & command, const wxSt
 bool BatchCommands::ApplyChain(const wxString & filename)
 {
    mFileName = filename;
-   unsigned int i;
-   bool res = true;
+
+   AudacityProject *proj = GetActiveProject();
+   bool res = false;
+   auto cleanup = finally( [&] {
+      if (!res) {
+         if(proj) {
+            // Chain failed or was cancelled; revert to the previous state
+            proj->RollbackState();
+         }
+      }
+   } );
 
    mAbort = false;
 
-   for (i = 0; i < mCommandChain.GetCount(); i++) {
-      if (!ApplyCommandInBatchMode(mCommandChain[i], mParamsChain[i]) || mAbort) {
-         res = false;
+   size_t i = 0;
+   for (; i < mCommandChain.GetCount(); i++) {
+      if (!ApplyCommandInBatchMode(mCommandChain[i], mParamsChain[i]) || mAbort)
          break;
-      }
    }
 
+   res = (i == mCommandChain.GetCount());
+   if (!res)
+      return false;
+
    mFileName.Empty();
-   AudacityProject *proj = GetActiveProject();
-
-   if (!res)
-   {
-      if(proj) {
-         // Chain failed or was cancelled; revert to the previous state
-         proj->RollbackState();
-      }
-      return false;
-   }
 
    // Chain was successfully applied; save the NEW project state
    wxString longDesc, shortDesc;

src/effects/EffectManager.h

@@ -91,7 +91,22 @@ public:
    bool HasPresets(const PluginID & ID);
    wxString GetPreset(const PluginID & ID, const wxString & params, wxWindow * parent);
    wxString GetDefaultPreset(const PluginID & ID);
+
+private:
    void SetBatchProcessing(const PluginID & ID, bool start);
+   struct UnsetBatchProcessing {
+      PluginID mID;
+      void operator () (EffectManager *p) const
+         { if(p) p->SetBatchProcessing(mID, false); }
+   };
+   using BatchProcessingScope =
+      std::unique_ptr< EffectManager, UnsetBatchProcessing >;
+public:
+   // RAII for the function above
+   BatchProcessingScope SetBatchProcessing(const PluginID &ID)
+   {
+      SetBatchProcessing(ID, true); return BatchProcessingScope{ this, {ID} };
+   }
 
    /** Allow effects to disable saving the state at run time */
    void SetSkipStateFlag(bool flag);