Re: get_immediate echoe character--compiled error?

[Keith Thompson <Keith.S.Thompson+u@gmail.com>]

Niklas Holsti <niklas.holsti@tidorum.invalid> writes:
> On 2023-10-04 11:22, Simon Wright wrote:
>> Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:
>>> Simon Wright <simon@pushface.org> writes:
>>>> The low-level Get_Immediate implementation is in sysdep.c (probably
>>>> not in the adainclude/ directory in an installed compiler), in
>>>> getc_immediate() and getc_immediate_nowait(), both of which call
>>>> getc_immediate_common(), and I can't see any difference! ECHO gets
>>>> turned off in getc_immediate_common(), regardless of caller - see
>>>> link.
>>>>
>>>> https://github.com/gcc-mirror/gcc/blob/3ca09d684e496240a87c0327687e2898060c2363/gcc/ada/sysdep.c#L387
>>>
>>> I haven't really looked into this, but I *think* what's happening is
>>> that for the versions with the Available parameter, ECHO hasn't yet been
>>> turned off when the user types the character.  If you type 'x', it
>>> echoes immediately, because the program has no way of knowing that the
>>> character will later be consumed by a call to Get_Immediate.  Presumably
>>> if the user hasn't typed anything, causing Available to be set to false,
>>> Get_Immediate will turn echoing off and back on again very quickly.
>>> Echoing is disabled only for small fraction of a second it takes for
>>> Get_Immediate to be executed.
>>>
>>> The Get_Immediate functions without the Available parameter block
>>> until a character is entered.  They can disable echoing before the
>>> character is entered.  Echoing will typically be disabled for minutes
>>> or seconds, from the time Get_Immediate is called and the time the
>>> user types something.
>>>
>>> The only solution I can think of would be to disable echoing (in some
>>> non-portable manner; I don't think the standard library provides this)
>>> before the user starts typing.  (Perhaps you want to run the
>>> Get_Immediate without the Available parameter in a separate task?)
>> Great analysis! 
>
>
> Yes indeed.
>
> A possible solution in Text_IO would be for Get_Immediate with
> Available not to enable echo when it exits. Get_Immediate with
> Available is typically called repeatedly, with no other input from the
> terminal in between these calls, so it should be ok to keep echo
> disabled from one such call to another. Any non-immediate input
> operation on the terminal (that is, on this Text_IO file) should start
> by re-enabling echo if it was disabled. Possibly the same should apply
> also to Get_Immediate without Available, that is, it should leave echo
> disabled, until some non-immediate input operation re-enables echo.

The *first* character typed would still echo.

I suggest that what's needed is a way to turn echoing on and off.

Meanwhile, would calling Get_Immediate *without* the Available parameter
(which blocks and turns echoing off until after a character is typed) in
a separate task work?  I haven't tried it.  Of course you'd need to be
careful not to have I/O calls from separate tasks interfere with each
other.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Will write code for food.
void Void(void) { Void(); } /* The recursive call of the void */