PostgreSQL listen/notify and the method stack

[Nick Renders]

Hi Doug,

I don't think the call to a $notify method is just added to the method stack. In my test, it interrupts the current method. I can send you a little demo library, if you like.

Thanks for the tip on keeping a list of notifications. I was thinking about having the $notify schedule a timer in order to queue the action, but this might be a more elegant solution.


Nick Renders


On 23 Nov 2023, at 14:29, Doug Easterbrook wrote:

> The other thing you can do if you are concerned is make a listen notify handler.  I have an example in the pgsqldam object in the sample code from  euromis
>
> If you get a notify,  then add it to a list of pending calls.   When you’d stack has diminished. Call a routine to process the pending notifies in the list and clean the list out
>
> That make notify nothing more than add line to pending list so it pretty much eliminates potential interaction with other code
>
> I don’t think you should worry about, but then I don’t know how much work you are doing in the notify
>
> ------------
> Doug Easterbrook
> Arts Management Systems Ltd.
> doug at artsman.com
>
>> On Nov 23, 2023, at 6:38 AM, Doug Easterbrook <doug at artsman.com> wrote:
>>
>> As far as I understand the timer is popped on the stack
>>
>> It’s the same as background workers
>>
>> So it eventually gets executed as the omnis stack winds down
>>
>> Just make sure your variable scope is right and you won’t have problems
>>
>>
>> All Timers act the same way
>>
>> ------------
>> Doug Easterbrook
>> Arts Management Systems Ltd.
>> doug at artsman.com
>>
>>> On Nov 23, 2023, at 2:48 AM, Nick Renders via omnisdev-en <omnisdev-en at lists.omnis-dev.com> wrote:
>>>
>>> Hello fellow Omnis-Potents,
>>>
>>> I have noticed that when implementing the $listen and $notify methods of the PostgreSQL DAM, the $notify method actually interrupts the current method stack. So when Omnis is executing a certain method, the notification will cut in, execute the $notify method, and return to the previous method where it left off. At least that is what I've come to understand after doing some tests.
>>>
>>> I'm not very comfortable with the $notify method interrupting any possible method at any possible time. Has anyone encountered this before? Does anyone have any good tips and/or tricks on managing listeners/notifiers?
>>>
>>> Best regards,
>>>
>>> Nick Renders
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