[Info-vax] VMS process communication

[Richard Maher]

On 14/09/2022 9:14 am, Arne Vajhøj wrote:
> On 9/13/2022 8:56 PM, Dave Froble wrote:
>> On 9/13/2022 8:38 PM, Arne Vajhøj wrote:
>>> On 9/13/2022 12:08 PM, Lee Gleason wrote:
>>>> On 9/12/2022 10:23 PM, Dave Froble wrote:
>>>>> On 9/12/2022 6:58 PM, Arne Vajhøj wrote:
>>>>>> I did a little writeup:
>>>>>> 
>>>>>> https://www.vajhoej.dk/arne/articles/vmsipc.html
>>> 
>>>>> Why no mention of mailboxs ?
>>>> 
>>>> And event flags and locks?
>>> 
>>> To me those are synchronization techniques not communication 
>>> techniques - or at least not general communication techniques.
>> 
>> As Rob pointed out, one can do a lot with the DLM.
>> 
>> Isn't synchronization itself a form of communication?
> 
> Yes.
> 
> But not what I would call general communication.
> 
> It is not intended to send arbitrary messages - it is intended to
> synchronize flows.
> 
> Arne
> 
> 
> 

Example: Trade Matching and Clearing system

Half-trades would come in as they happen.
Supplier process simply cannot be write to an ISAM file quick enough to 
keep up.
If Consumer process reads past eof of matching sequential queue file it 
will have to close the SEQ file, open it again and re-read the many 
thousands of already processed trades to get back up to dat.

Solution: Lock Value Block

The ID of the last txn written is stored in the LVBLK.
When the Consumer obtains the lock and discovers the last txn available 
is the same as the last it just processed it goes to sleep and waits for 
a BLAST from the producer.

Summary: I call that interprocess communication