Delphi’s memory manager checks IsMultiThread and uses critical sections to protect the integrity of its internal data structures. Therefore, if you create a thread by calling the Windows API function CreateThread, you must explicitly set IsMultiThread to True.

Delphi also sets IsMultiThread to True for web servers and COM servers that don’t force single threading (tmSingle threading model).

If you write your own DLL that might be loaded by a multithreaded application, set IsMultiThread to True. If you use DllProc to learn when more than one thread attaches to the DLL, you must realize the application might start multiple threads before loading the DLL.