Re: Advice, tasking and hardware

[Shark8 <onewingedshark@gmail.com>]

On Friday, May 27, 2016 at 1:50:50 AM UTC-6, Dmitry A. Kazakov wrote:
> 5. Tasks entries have parameter passing problems. If you don't handle 
> everything in the rendezvous in order to release the caller as soon as 
> possible, you need to copy parameters and store them locally. The design 
> of the select statement prevents doing this in a structured way. E.g.
> 
>     select
>        accept String_Call (Text : String) do
>           Local_Text := Text; -- Accept scope
>        end;
>        declare -- Handler's scope
>           Local_Text : String -- This does not work!
>        begin
>           -- Process Local_Text
>        end;
>     or accept ...

Pretty much a non-problem in Ada 2012:

    package Example is
	
	Task Text_IO is
	    Entry Get( Data : String );
	    Entry Put;
	    Entry Done;
	End Text_IO;
	
    end Example;
    
    package body Example is
	
	Task Body Text_IO is
	    Package String_Holder is new Ada.Containers.Indefinite_Holders(
	      Element_Type => String );

	    Internal_Data : String_Holder.Holder:= String_Holder.To_Holder("");
	    Finished      : Boolean := False;
	begin
	    loop
		select
		    accept Done do
			Finished:= True;
		    end Done;
		or
		    accept Get (Data : in String) do
			Internal_Data:= String_Holder.To_Holder( Data );
		    end Get;
		or
		    accept Put do
			Ada.Text_IO.Put_Line( "DATA: "& Internal_Data.Element );
		    end Put;
		end select;
		
		Exit when Finished;
	    end loop;
		
	End Text_IO;
	
    end Example;

and used via:
    Example.Text_IO.Put;
    Example.Text_IO.Get( "Test Data" );
    Example.Text_IO.Put;
    Example.Text_IO.Get( "Something Else" );
    Example.Text_IO.Put;

    Example.Text_IO.Done;

> 6. Task entries cannot return unconstrained objects.

This can be worked around:
   We can add to the previous task the following:
	    Entry Data( Item : out Natural );
	    Entry Data( Item : out String );
   Where the one returns the constraints needed for the other... it would be used something like this:
    declare
	Length : Natural renames Example.Text_IO.Data;
	Test   : constant String(1..Length):= Example.Text_IO.Data;
    begin
	Put_Line ( "----- " & Test & " -----" );
    end;