[Info-vax] VMS enhancement suggestion: Add a "read regardless" file open option.

[Hein RMS van den Heuvel]

On Monday, November 9, 2020 at 5:35:32 PM UTC-5, Tom Wade wrote:
> On 2020-11-09 13:30, Simon Clubley wrote: 
> > On RSTS/E, you can view the contents of a file opened for write by 
> > specifying mode 4096 as in: 
> > 
> > pip filename.dat/mo:4096 
> > 
> > What would be involved in adding a "read regardless" file open option 
> > to VMS which would allow the opening of files for read only even if 
> > they are already open for write, and then adding a qualifier to $ TYPE 
> > to use this new option ?
> If you want to read files that are locked by another process, check out 
> the Ralf utility at www.tomwade.eu/software 
> 
> Ralf is written as a callable utility, but has a command line PEEK 
> [/page] program that displays a locked file. We used it extensively to 
> examine PMDF message files that were being processed (and therefore locked). 
> 
> 
> Tom Wade 
> tom dot wade at tomwade dot eu

Well, it will only be partially useful as many such files write-no-share file are written by RMS or an RTL actively buffering data to be written in incomplete chucks.
RMS by default could have an 8KB or 16 KB  buffer only written when full. The most recent record will only exist in process memory. RMS has a minor backdoor to try an flush on exit, but I don't think there is a way to jiggle that conditions. So it could all be very disappointing.

You can verify with BACK/IGNORE=INTERLOCK whether it would or would not sufficiently solve a good part of the business needs.
I hope it is clear it will not at all be what folks expect and very hard to explain.

To properly solve this and similar problem you really need a system buffer.
 RMS/VMS engineering spend upwards of 2 manyears to define 'stream' file access back in the 90ies  but nothing practical transpired.
I believe most solution still ended up with the applications needing to 'do' something, which is the very thing that we all want to avoid.

As Brian says it may be easier hack the applications (Patch!) to initialize the fabs with sharing option and take the 'hit' of the locking overhead.

Cheers,
Hein