XCLN: Synchronization of Offline Folders over RAS or Net Hangs

The information in this article applies to:

• Microsoft Exchange Server, version 5.0

SYMPTOMS

When you synchronize offline folders over RAS or the network, Microsoft Exchange Server 5.0 periodically stops responding. The progress dialog box on the screen is still animated, it but does not advance, leaving the network or RAS connection open. Moving the mouse causes synchronization to resume.

CAUSE

The problem is in the behavior of the Win32 API MsgWaitForMultipleObjects as it is used by the Windows NT notification engine in its ScMsgWaitForSignal call. MsgWaitForMultipleObjects does not notice a window message posted from the notification thread to the main thread, enabling it to deliver pending notifications. The reason is that the message was PeekMessage'd by code in the main thread (may have been OLE, but could be anywhere) and MsgWaitForMultipleObjects interprets peeked messages as intentionally left on the queue, and therefore does not return as it does with new, unpeeked messages. In our case the message is responsible for initiating delivery of notifications, but because the thread is waiting for notifications to be delivered, the process stops until a genuinely new message (such as a mouse move) is posted to the message queue.

STATUS

Microsoft has confirmed this to be a problem in Microsoft Exchange Server version 5.0. This problem was corrected in the latest Microsoft Exchange Server 5.0 U.S. Service Pack. For information on obtaining the service pack, query on the following word in the Microsoft Knowledge Base (without the spaces):