Bugfix: There is no thread safety mechanism in Zeos for the SQL log, so implement one in HeidiSQL. This should speed up async queries tremendously, as they no longer have to wait for the GUI to repaint before firing the actual query. Haven't bothered thinking about thread safety around the creation of the critical section protecting the TStringList, mainly because I'm infinitely annoyed by Delphi not providing a thread-safe list capable of holding lists OOTB..

source/childwin.pas

@@ -510,6 +510,7 @@ type
         Column: TColumnIndex; var LineBreakStyle: TVTTooltipLineBreakStyle; var
         HintText: WideString);
     procedure popupFilterPopup(Sender: TObject);
+    procedure ProcessSqlLog;
 
     private
       strHostRunning             : String;
@@ -534,6 +535,8 @@ type
       TablePropertiesForm        : Ttbl_properties_form;
       FileNameSessionLog         : String;
       FileHandleSessionLog       : Textfile;
+      SqlMessages                : TStringList;
+      SqlMessagesLock            : TRtlCriticalSection;
 
       function GetQueryRunning: Boolean;
       procedure SetQueryRunning(running: Boolean);
@@ -764,6 +767,10 @@ begin
   UserQueryFiring := False;
   TemporaryDatabase := '';
   CachedTableLists := TStringList.Create;
+  InitializeCriticalSection(SqlMessagesLock);
+  EnterCriticalSection(SqlMessagesLock);
+  SqlMessages := TStringList.Create;
+  LeaveCriticalSection(SqlMessagesLock);
 
   FConn := AConn^;
   FMysqlConn := AMysqlConn; // we're now responsible to free it
@@ -1087,6 +1094,9 @@ begin
   SetWindowConnected( false );
   SetWindowName( main.discname );
   Application.Title := APPNAME;
+  EnterCriticalSection(SqlMessagesLock);
+  FreeAndNil(SqlMessages);
+  LeaveCriticalSection(SqlMessagesLock);
 
   // Closing connection and saving some vars into registry
   case ( WindowState ) of
@@ -1173,7 +1183,30 @@ begin
     msg := '/* ' + msg + ' */';
   end;
 
-  SynMemoSQLLog.Lines.Add( msg );
+  EnterCriticalSection(SqlMessagesLock);
+  try
+    SqlMessages.Add(msg);
+  finally
+    LeaveCriticalSection(SqlMessagesLock);
+  end;
+  PostMessage(MainForm.Handle, WM_PROCESSLOG, 0, 0);
+end;
+
+procedure TMDIChild.ProcessSqlLog;
+var
+  msg: string;
+begin
+  EnterCriticalSection(SqlMessagesLock);
+  try
+    if SqlMessages = nil then Exit;
+    if SqlMessages.Count < 1 then Exit;
+    msg := SqlMessages[0];
+    SqlMessages.Delete(0);
+  finally
+    LeaveCriticalSection(SqlMessagesLock);
+  end;
+
+  SynMemoSQLLog.Lines.Add( String(msg) );
   SynMemoSQLLog.GotoLineAndCenter( SynMemoSQLLog.Lines.Count );
   SynMemoSQLLog.Repaint();
 
@@ -1834,7 +1867,7 @@ end;
 procedure TMDIChild.WaitForQueryCompletion(WaitForm: TForm);
 begin
   debug( 'Waiting for query to complete.' );
-  WaitForm.ShowModal();
+    WaitForm.ShowModal();
   debug( 'Query complete.' );
 end;
 

source/communication.pas

@@ -23,6 +23,7 @@ uses
 const
   // Our custom message types.
   WM_COMPLETED        = WM_APP + 1;
+  WM_PROCESSLOG       = WM_APP + 2;
   // Our message subtypes for WM_COPYDATA messages.
   CMD_EXECUTEQUERY_NORESULTS     = 1; { Slightly faster  - Fire-and-forget, no results }
   CMD_EXECUTEQUERY_RESULTS       = 2; { Normal           - Wait for completion, fetch results }

source/main.pas

@@ -195,6 +195,7 @@ type
     procedure ExecuteRemoteNonQuery(sender: THandle; query: string);
     procedure HandleWMComplete(var msg: TMessage); message WM_COMPLETED;
     procedure HandleWMCopyData(var msg: TWMCopyData); message WM_COPYDATA;
+    procedure HandleWMProcessLog(var msg: TMessage); message WM_PROCESSLOG;
   private
     function GetChildwin: TMDIChild;
   public
@@ -276,6 +277,11 @@ begin
   HandleWMCopyDataMessage(msg);
 end;
 
+procedure TMainForm.HandleWMProcessLog(var msg: TMessage);
+begin
+  ChildWin.ProcessSqlLog;
+end;
+
 procedure TMainForm.EnsureConnected;
 begin
   if ActiveMDIChild = nil then raise Exception.Create('Not connected.');