Re: confusion about message passing between the tasks

[Brad Moore <brad.moore@shaw.ca>]

On 2014-10-26 2:42 PM, Dmitry A. Kazakov wrote:
> An extreme scenario (unfortunately not Ada's annex E), a distributed system
> could be decomposed around rendezvous between tasks running on physically
> distributed nodes. This cannot be done with PO.
>


Why not with Ada's annex E? For instance, you can have a remote access 
to class-wide type that is an interfaces, including protected interfaces 
and task interfaces.

I have some examples of Remote buffers that have task interfaces in the 
dequesterity project.

For instance calling the Read or Write interface primitives can result 
in a rendezvous with a remote task object.

The same can be done with remote protected interfaces, and I have 
working examples of that as well.

eg.


generic
    type Element_Type is private;
    pragma Preelaborable_Initialization (Element_Type);

...

package Buffers is

    pragma Pure;

    ...

    type Remote_Buffer_Interface is limited interface;

    function Read
      (From : Remote_Buffer_Interface)
       return Element_Type is abstract;

    procedure Write
      (To   : in out Remote_Buffer_Interface;
       Item : Element_Type) is abstract;

...
end Buffers;


...
package Buffers.Active is

    pragma Pure;
    pragma Remote_Types;  -- Not needed since implied by pragma Pure

    task type Buffer
      (Maximum_Capacity : Count_Type;
       Task_Priority : System.Priority;
       Maximum_Read_Block : Timeout_In_Milliseconds_Type;
       Maximum_Write_Block : Timeout_In_Milliseconds_Type;
       Maximum_Exclusive_Lock_Time : Timeout_In_Microseconds_Type)
    is new Vectored_Buffer_Interface with

       pragma Priority (Task_Priority);

       overriding entry Read (Item : out Element_Type);

       overriding entry Write (Item : Element_Type);
       ...

    end Buffer;

    ....
end Buffers.Active;

Brad