[Info-vax] DCL "READ/TIME_OUT=n" from terminal; timer resets if message written to screen

[Dave Froble]

On 5/24/2021 8:39 AM, Simon Clubley wrote:
> On 2021-05-22, Volker Halle <volker_halle at hotmail.com> wrote:
>> Scott,
>>
>> this is expected and documented behaviour. It has nothing to do with DCL.
>>
>> https://vmssoftware.com/docs/VSI_IO_REF.pdf
>>
>> Table 5.6. Read QIO Function Modifiers for the Terminal Driver
>>
>> IO$M_TIMED ...
>> If a read operation is interrupted by either a broadcast write or a synchronous write request, the timer operation is restarted.
>>
>> Volker.
>
> What could the point of that behaviour possibly be ???
>
> This sounds to me like someone added timeout support to the terminal driver,
> found a bug where the timer gets reset on terminal writes, could not find
> a way to easily fix it, so they ended up documenting the bug as expected
> behaviour. :-)
>
> If that wasn't the case, and this was actually intended behaviour, then
> what could the reasoning for this behaviour possibly be ?
>
> And before everyone jumps on me, just remember that we talking about
> a driver that is apparently so convoluted internally that adding code
> to allow editing of lines longer than the terminal width is apparently
> not viable to do (even though you can do this just fine on other operating
> systems).
>
> Simon.
>

Well, Ok, perhaps time for some "devil's advocate" ...

There might be circumstances where if an AST on "something" is 
triggered, timer ASTs also get triggered/deleted.

Having written that, it's not something I'd want ...

Which might lead to the question of "how does a timer AST get triggered?"

No source code, so some speculation.  A timer AST using a delta time 
probably checks the current time, add the delta time, and sets an AST 
for the calculated actual time.  If so, then the absolute time for the 
timer AST to trigger is known (to something), and so I'd ask, why isn't 
the timer AST reset using the actual time to trigger?

Just wondering why it's implemented as it currently exists ...

-- 
David Froble                       Tel: 724-529-0450
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