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

[Simon Clubley]

On 2021-05-24, Arne Vajhøj <arne at vajhoej.dk> wrote:
> On 5/24/2021 7:53 PM, Dave Froble wrote:
>> On 5/24/2021 2:12 PM, Simon Clubley wrote:
>>> On 2021-05-24, David Jones <osuvman50 at gmail.com> wrote:
>>>> I imagine read/time_out=... is using the timeout feature of the 
>>>> terminal driver
>>>> and not timer ASTs. The timeout is a feature of the wait for 
>>>> interrupt function
>>>> in the kernel, which is why it resets for every character entered (as 
>>>> well as
>>>> breakthru writes).
>>>
>>> _If_ that is the case, then the read timeout functionality is broken
>>> IMHO because that is _very_ unexpected behaviour.
>> 
>> I don't agree with what you wrote.  Yes, I'd prefer a bit different 
>> operation, but, I can understand and accept what's there.  Maybe could 
>> be better, but, not broken.

It's unexpected because most people are not going to find the one
paragraph deep in a low-level programmer's manual that documents this.

They are going to look at other documentation sources where this very
unexpected behaviour is not documented.

>
> I agree.
>
> Not only is it what's there.
>
> As it turned out then it is actually documented behavior.
>
> Actual behavior is expected to follow documented behavior.
>
> It is almost guaranteed that there will be some functionality
> where ones expectation without reading the documentation is
> different from actual behavior.
>

This is the documented behaviour that most people are going to read:

---------------------------------------------------------------------------
READ

  /TIME_OUT

        /TIME_OUT=n
        /NOTIME_OUT (default)

     Specifies the number of seconds after which the READ command is
     terminated if no input is received. If you enter the /TIME_OUT
     qualifier, you must specify a value from 0 to 255.

     If you enter both the /ERROR=label and /TIME_OUT qualifiers, and
     the time limit expires, the error branch is taken.
---------------------------------------------------------------------------

That text is simple, clear to understand, and completely wrong.

Simon.

-- 
Simon Clubley, clubley at remove_me.eisner.decus.org-Earth.UFP
Walking destinations on a map are further away than they appear.