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From: BEB@UNO.BITNET
Newsgroups: comp.os.vms
Subject: Re: Re: interprocess communication without privs
Message-ID: <8709250952.AA07381@ucbvax.Berkeley.EDU>
Date: Wed, 23-Sep-87 16:50:00 EDT
Article-I.D.: ucbvax.8709250952.AA07381
Posted: Wed Sep 23 16:50:00 1987
Date-Received: Sat, 26-Sep-87 19:32:03 EDT
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<Mailers are mudders. This line is mudder fodder, brudder.>

>From:         Jamie Hanrahan <UCSDHUB!JACK!MAN!CRASH!JEH@SDCSVAX.UCSD.EDU>
>
>A previously-posted summary of the standard interproc. comm. techniques
>(can't seem to find the article, or I'd run this as a followup thereto)
>was quite good.  I can only add two things:  First, global sections
>alone are not enough -- you also need an interproc. synchronization
>technique to control access to the section.  This can be common event
>flags (limited to procs within a UIC group), hiber/wake, or the lock
>manager.  Which is more suitable depends on the function you want.

Or use the BBSSI inst to implement mutual exclusion routines. Example:

        .Entry  MUTEXON,^M<>            ; loop til MUTEX_FLAG cleared, then set
1$:     BBSSI   #0,@MUTEX_FLAG,1$       ; where MUTEX_FLAG is in global section
        MOVB    #1,@4(ap)               ; we have control
        RET

        .Entry  MUTEXOFF,^M<>           ; give up control of global section
        CLRB    @MUTEX_FLAG             ; clear flag in global section space
        CLRB    @4(AP)                  ; return "no control" status
        RET

Or for Macro haters, the LIB$BBSSI RTL routine allows a HLL access to the
BBSSI inst. Of course you immediately notice this turkey is a polling loop
gobbling CPUtime like there is no DD-MMM-YYYY +1. Well, for an (user
interactive) application that can hibernate and wake up, say, ten or more
times a second, it works very well, and isn't too expensive, depending on
how much you have to do every time it wakes up, how much contention for
mutex, etc... The big win here is that it is really simple to set up. Just
create your global section and bracket any code that munges on it with the
mutexon/mutexoff calls.
                                            Bruce

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<>Handle:   Bruce Bettis        <>USnail:   University of New Orleans <>
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