From:	CSBVAX::MRGATE!RELAY-INFO-VAX@CRVAX.SRI.COM@SMTP  8-AUG-1988 12:49
To:	ARISIA::EVERHART
Subj:	Re: Multiple-access files in VMS


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Date:      Mon,  8 Aug 88 08:23:44 CDT
To:        <INFO-VAX@KL.SRI.COM>
From:      "John Hascall" <GG.SPY%ISUMVS.BITNET@CUNYVM.CUNY.EDU>
Subject:   Re: Multiple-access files in VMS

> Date:         Mon, 1 Aug 88 14:12:09 EST
> From:         "Richard B. Gilbert" <dragon@NSCVAX.PRINCETON.EDU>
> Subject:      Multiple-access files in VMS
> Comments: To: Mike Temkin <cs.utexas.edu!sm.unisys.com!csun!mst@RUTGERS.EDU>
>
>    Mike Temkin writes:
>>Does anyone out there know how to make a file multi-accessible (readwise)
>>in VMS?  There must be a way since I would think that the help file is
>>that way.  Any help is appreciated.
>
>    Sharability is not an attribute of a VMS file.  File sharing is
> controlled by the bits in FAB$B_SHR in the File Access Block (FAB) which
> are set when a program opens the file.  As soon as a program opens a file
> for exclusive access, it is no longer shareable.

  You can, however, set the flag FAB$V_RRL (Read Regardless of Lock) in
FAB$L_FOP (at least in MACRO, I don't know if any of the high-level
languages provide a way to do this).

>    Any program that opens a file to write to it will almost certainly open
> it for exclusive access.  Programs written in high level languages
> sometimes default to exclusive access.  From VAX Fortran, for example, the
> OPEN statement must include the keyword SHARED, else the file is opened for
> exclusive access, (FAB$B_SHR=FAB$V_NIL).
>

John Hascall
ISU Comp Center