Unit ThreadSyncTest;

{ This unit is aimed at tracking down a very specific bug.  Sometimes
  Thread.Synchronize does not do what it is supposed to to.  It calls the
  method in the current thread, not the main GUI thread.

  It turns out that Delphi's Thread.Syncrhonize works exactly as it should.
  The bug was in my code.  I wasn't calling Thread.Synchronize when I thought
  I was.  D'oh!
}

Interface

  Procedure DoThreadSyncTest;

Implementation

  Uses
    Windows, Classes, SysUtils;

  Type
    TTestThread =
      Class(TThread)
      Protected
        Procedure Execute;  Override;
        Procedure InGuiThread;
      End;

  Procedure TTestThread.Execute;
    Var
      OtherThread : TTestThread;
    Begin
      Try
        Assert(GetCurrentThreadId <> MainThreadId, 'Problem before Sync.');
        OtherThread := TTestThread.Create(True);
        OtherThread.
        Synchronize(InGuiThread);
        Assert(GetCurrentThreadId <> MainThreadId, 'Problem after Sync.');
      Except
        On Ex : Exception Do
          Begin
            { Past experience shows that Delphi is very bad about reporting
              exceptions in any thread but the GUI thread. }
            MessageBox(0, PChar(Ex.Message), PChar(Ex.ClassName+''), 0);
            Halt
          End
      End
    End;

  Procedure TTestThread.InGuiThread;
    Begin
      Assert(GetCurrentThreadId = MainThreadId, 'Problem in Sync.')
    End;

  Procedure DoThreadSyncTest;
    Var
      TestThread : TTestThread;
    Begin
      TestThread := TTestThread.Create(True);
      TestThread.FreeOnTerminate := True;
      TestThread.Resume
    End;


End.