Path: utzoo!attcan!uunet!auspex!guy
From: guy@auspex.auspex.com (Guy Harris)
Newsgroups: comp.unix.wizards
Subject: Re: How do I know my Q-KEY is unique ?
Keywords: msg queue, queue, message queue, ID
Message-ID: <2492@auspex.auspex.com>
Date: 24 Sep 89 00:12:15 GMT
References: <1747@draken.nada.kth.se> <1196@virtech.UUCP>
Reply-To: guy@auspex.auspex.com (Guy Harris)
Organization: Auspex Systems, Santa Clara
Lines: 24

>There is no way to "register" or reserve an IPC key value.  Most software
>that I have seen using ipc's has used one of the following:
>
>	[methods 1, 2, 3, and 4]

5. Pick some file as a "rendezvous" point, and use "ftok".

To quote the SunOS 4.0 version of the "ftok" manual page:

     All interprocess communication facilities require  the  user
     to  supply a key to be used by the msgget(2), semget(2), and
     shmget(2) system calls to obtain interprocess  communication
     identifiers.   One  suggested method for forming a key is to
     use the ftok() subroutine described below.  Another  way  to
     compose keys is to include the project ID in the most signi-
     ficant byte and to use the remaining portion as  a  sequence
     number.   There  are many other ways to form keys, but it is
     necessary for each system to define  standards  for  forming
     them.  If some standard is not adhered to, it will be possi-
     ble for unrelated  processes  to  unintentionally  interfere
     with each other's operation.  Therefore, it is strongly sug-
     gested that the most significant byte of a key in some sense
     refer  to  a  project  so that keys do not conflict across a
     given system.