PRB: Messages Sent to Mailslot Are Duplicated

• Microsoft Win32 Application Programming Interface (API) included with:

      - Microsoft Windows NT versions 3.5 and 3.51
      - Microsoft Windows 95 version 4.0
  

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.