Re: Ichbiah 2022 compiler mode

[Niklas Holsti <niklas.holsti@tidorum.invalid>]

On 2024-09-12 7:46, Randy Brukardt wrote:
> "Niklas Holsti" <niklas.holsti@tidorum.invalid> wrote in message
> news:lk3fsvF7aaaU1@mid.individual.net...
> ...
>> I disagree with Randy's view that tasks and "parallel" are much
>> overlapping. Tasks are able to communicate with each other, but AIUI
>> parallel tasklets are not meant to do that, and may not be able to do
>> that. Tasks can have different priorities; tasklets cannot.
> 
> I was (of course) presuming that "tasklets" would get those capabilities if
> they were to replace tasks. That's what I meant about "suspension", which is
> not currently allowed for threads in Ada (parallel code is not allowed to
> call potentially blocking operations). If that was changed, then all forms
> of existing task communication would be allowed.


Ok, I understand. In that case, what "parallel" adds to the current 
tasking feature is an easy way to create a largish and perhaps 
dynamically defined number of concurrent threads from a "parallel" loop, 
where the threads are automatically created when the loop is started and 
automatically "joined" and destroyed when the loop completes.

I don't mind at all if a future Ada evolution merges tasks and 
"parallel", although it might defeat the easier access to multi-core 
true parallelism that is the goal of the "parallel" extension, AIUI.


> I'm less certain about the value of priorities, most of the time, they don't
> help writing correct Ada code. (You still need all of the protections
> against race conditions and the like.) I do realize that they are a natural
> way to express constraints on a program. So I admit I don't know in this
> area, in particular if there are things that priorities are truly required
> for.


Priorities (or the equivalent, such as deadlines) are absolutely 
required for real-time systems where there are fewer cores than 
concurrent/parallel activities so that the system has to schedule more 
than one such activity on one core.

If Ada did not have tasks with priorities, most of the Ada applications 
I have worked on in my life would have had to avoid Ada tasking and 
retreat to using some other real-time kernel, with ad-hoc mapping of the 
kernels's threads to Ada procedures.

Despite the transition to multi-core processors, I think that there will 
continue to be systems where scheduling is required, because the number 
of concurrent/parallel activities will increase too.