BUG: DdeConnect Never Returns

A 32-bit application calls DdeConnect when all previous DDEML initialization has been performed. DdeConnect never returns.

Any thread that creates a top-level window and doesn't have a message loop will cause DdeConnect to block. This is because DdeConnect calls SendMessage(HWND_BROADCAST...). In this call, SendMessage will put the message in the target thread's message queue and block the calling thread. If the target thread doesn't have a message loop, it will never process this message and therefore never return.

One complication is that some things create windows without the knowledge of the calling thread. It is known that some SQL, RPC, and DDEML function calls will do this. Any top-level window that is created by a thread that has no message loop will cause this to happen.

The only current solution is to add a message loop to the thread that created the window.

Microsoft has confirmed this to be a problem in the Microsoft products listed at the beginning of this article.