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

[Dave Froble]

On 11/10/2020 6:16 PM, Craig A. Berry wrote:
>
> On 11/10/20 3:48 PM, Jim wrote:
>> On Tuesday, November 10, 2020 at 10:06:29 AM UTC-5, Craig A. Berry wrote:
>>> On 11/10/20 7:25 AM, Simon Clubley wrote:
>>>> On 2020-11-09, Dave Froble <da... at tsoft-inc.com> wrote:
>>>
>>>>> Seems like VAX Basic has a "read regardless" lock qualifier ...
>>>>>
>>>>
>>>> I wasn't aware of that. Does it allow you to open a sequential file for
>>>> reading while the file is also in the process of being created by
>>>> another
>>>> program ? You can clearly do it for batch log files but what about
>>>> programs
>>>> that don't specify that writing mode when creating a sequential file ?
>>>>
>>>>> Might that be helpful?
>>>>>
>>>>> And of course RMS would have the capability.
>>>>>
>>>>
>>>> Interesting. One of the issues that was raised when I moved from RSTS/E
>>>> to VMS in the early 1990s was that a VMS version of mode 4096 didn't
>>>> exist and I wasn't aware it had been added in the meantime.
>
>>> Search for "OpenVMS RMS RAB$V_RRL" and see how it works. That's
>>> record-level, though, not file-level.
>>
>> For file level access - search for fib$v_nolock or fib$m_nolock
>
>
> Ah, yes, I either forgot or didn't know about that.  But it looks like
> that's ACP-level only and doesn't fit Dave Froble's statement that I was
> responding to, i.e., that whatever BASIC does, "RMS would have the
> capability" because with FIB$M_NOLOCK you have to do a $QIO to open the
> file.  Hein has a nice write-up here:

http://h30266.www3.hpe.com/odl/vax/progtool/cpqbasic39/bas_ref_021.htm#index_x_1706

Read about the USEROPEN in a file OPEN statement.  Basically (sic) the 
FAB and RAB (I believe) are populated, then the USEROPEN routine, 
provided by the programmer, can set or clear FAB and RAB fields, and 
then do the actual file open.

http://h30266.www3.hpe.com/odl/vax/progtool/cpqbasic39/bas_ref_015.htm#index_x_1228

Read about the GET statement, and the REGARDLESS lock clause.

Basic(ally) (sic), it's in there ....

-- 
David Froble                       Tel: 724-529-0450
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