Preparations for issue #787:

* Moved call to SetEvent() from TBaseVirtualTree.ValidateCache() to TWorkerThread.AddTree() so that we can move WorkEvent variable to implementation section.
* Extracted private class procedures EnsureCreated() and Dispose() in TWorkerThread

Author: joachimmarder

Source/VirtualTrees.WorkerThread.pas

@@ -13,7 +13,9 @@   TWorkerThread = class(TThread)
     FCurrentTree: TBaseVirtualTree;
     FWaiterList: TThreadList;
     FRefCount: Cardinal;
-  protected
+    class procedure EnsureCreated();
+    class procedure Dispose();
+  strict protected
     procedure CancelValidation(Tree: TBaseVirtualTree);
     procedure Execute; override;
   public
@@ -33,7 +35,6 @@ procedure ReleaseThreadReference(Tree: TBaseVirtualTree);
 
 var
   WorkerThread: TWorkerThread = nil;
-  WorkEvent: THandle;
 
 
 implementation
@@ -47,11 +48,13 @@ implementation
   TBaseVirtualTreeCracker = class(TBaseVirtualTree)
   end;
 
+var
+  WorkEvent: THandle;
 //----------------- TWorkerThread --------------------------------------------------------------------------------------
 
-procedure AddThreadReference;
-begin
-  if not Assigned(WorkerThread) then
+class procedure TWorkerThread.EnsureCreated();
+begin
+  if not Assigned(WorkerThread) then
   begin
     // Create an event used to trigger our worker thread when something is to do.
     WorkEvent := CreateEvent(nil, False, False, nil);
@@ -61,6 +64,20 @@ procedure AddThreadReference;
     // Create worker thread, initialize it and send it to its wait loop.
     WorkerThread := TWorkerThread.Create();
   end;
+end;
+
+class procedure TWorkerThread.Dispose();
+begin
+  WorkerThread.Terminate();
+  SetEvent(WorkEvent);
+  WorkerThread := nil; //Will be freed usinf TThreaf.FreeOnTerminate
+  CloseHandle(WorkEvent);
+end;
+
+
+procedure AddThreadReference;
+begin
+  TWorkerThread.EnsureCreated();
   Inc(WorkerThread.FRefCount);
 end;
 
@@ -77,12 +94,7 @@ procedure ReleaseThreadReference(Tree: TBaseVirtualTree);
     TBaseVirtualTreeCracker(Tree).InterruptValidation;
 
     if WorkerThread.FRefCount = 0 then
-    begin
-      WorkerThread.Terminate();
-      SetEvent(WorkEvent);
-      WorkerThread := nil; //Will be freed usinf TThreaf.FreeOnTerminate
-      CloseHandle(WorkEvent);
-    end;
+      WorkerThread.Dispose();
   end;
 end;
 
@@ -202,6 +214,8 @@ procedure TWorkerThread.AddTree(Tree: TBaseVirtualTree);
   finally
     FWaiterList.UnlockList;
   end;
+
+  SetEvent(WorkEvent);
 end;
 
 //----------------------------------------------------------------------------------------------------------------------

Source/VirtualTrees.pas

@@ -25575,7 +25575,7 @@ procedure TBaseVirtualTree.UpdateWindowAndDragImage(const Tree: TBaseVirtualTree
 
 //----------------------------------------------------------------------------------------------------------------------
 
-procedure TBaseVirtualTree.ValidateCache;
+procedure TBaseVirtualTree.ValidateCache();
 
 // Starts cache validation if not already done by adding this instance to the worker thread's waiter list
 // (if not already there) and signalling the thread it can start validating.
@@ -25589,7 +25589,6 @@ procedure TBaseVirtualTree.ValidateCache;
   begin
     // Tell the thread this tree needs actually something to do.
     WorkerThread.AddTree(Self);
-    SetEvent(WorkEvent);
   end;
 end;