Microsoft KB Archive/127905

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PRB: Messages Sent to Mailslot Are Duplicated

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Q127905

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The information in this article applies to:


 * Microsoft Win32 Application Programming Interface (API), included with:
 * the operating system: Microsoft Windows NT, versions 3.5, 3.51
 * Microsoft Windows 95

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SYMPTOMS
One application creates a mailslot using CreateMailSlot and reads from it using ReadFile. A second application opens the mailslot using CreateFile and writes to it using WriteFile. The second application writes one message to the mailslot, but the first application receives three duplicates of the message.

CAUSE
This is expected behavior if you have three network transports loaded. There is no way to know which transport should be used to deliver to a given mailslot on a remote machine, so all transports are used.

RESOLUTION
Send a unique ID at the beginning of each message. The listening end can detect duplicates and delete them. If you have multiple clients sending messages, their messages may be interleaved in the mailslot. You may need to track which client sent which message last, in order to successfully detect duplicates.

STATUS
This behavior is by design.

Additional query words:

Keywords : kbOSWinNT350 kbOSWinNT351 kbOSWin95

Issue type :

Technology : kbAudDeveloper kbWin32sSearch kbWin32API