[Info-vax] Most popular application programming languages on VMS ?

[Chris Scheers]

Dave Froble wrote:
> On 1/10/2019 4:39 PM, John Reagan wrote:
>> I was discussing with Rob that the documentation for that DLM feature
>> is probably buried in some New Features manual or in some CRTL update
>> document.  It might not be written down anywhere (it probably
>> should).
>>
>> The CRTL uses the DLM with the range feature (don't think of them as
>> bytes in a file, but just a specialization of a normal named lock) to
>> be notified of multiple programs that are using the CRTL's
>> implementation of fcntl().
>>
>> http://pubs.opengroup.org/onlinepubs/9699919799/ and search for
>> "fcntl".
> 
> I'll take a look, but, I don't see how any resource name, being treated 
> solely as a resource name, could implement numeric range (better term 
> than byte range) locking.

Remember, the DLM doesn't actually lock anything.  It is a cooperative tool.

So, when you lock a range of a resource, you are locking the range of 
numbers from A to B for that resource.  If any other process tries to 
lock an overlapping range, the DLM will help to resolve the conflict.

If cooperative processes agree that a certain file is represented by a 
given resource name and that the lock ranges correspond to bytes in the 
file, you have file byte range locking for those cooperative processes.

If implemented in RMS, all processes that access the file through RMS 
will inherit this behavior.

BTW: I believe that range locking was added to the DLM for POSIX 
support.  So it goes back to at least whenever POSIX support was 
implemented.  (VMS 6?  VMS 5.5?)  I have NEVER seen it documented (New 
Features or otherwise) outside of the sources.

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Chris Scheers, Applied Synergy, Inc.

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