Re: Interrupts handling in ADA

[Ada BRL <ada.brl.2011@gmail.com>]

On 10 Dic, 22:27, Simon Wright <si...@pushface.org> wrote:
> "Ada @ BRL" <ada.brl.2...@gmail.com> writes:
>
> > The environment of ADA applcation is:
>
> Ada, please!
>
>
>
> > I have 4 tasks that execute at the same time:
> > one is the main task,
> > the other three execute a "read" from network (socket) function inside
> > their bodies (on the other side there's the C/C++ application with 3
> > network sockets).
> [...]
> > I want that when new data is available on one or more socket threads,
> > this / these threads somehow notify the main thread that data is
> > arrived and then safely send the data to it.
>
> First off, I'd use a Queue.
>
> The new Ada2012 standard includes a synchronised Queue, which would be
> just what you want out of the box, but you won't find that in the
> current compilers, so you'll need to roll your own.
>
> Starting from Ada.Containers.Vectors[1], the Queue abstraction would
> come from using Append to put new mesages on the queue, Is_Empty to
> check whether there's something to get from the queue, and First_Element
> followed by Delete_First to fetch the front element.
>
> You then need to wrap this container in a protected object[2], so that
> the updates from the different input tasks don't corrupt each other, and
> so that the main task can block until there's something to read. Use a
> Put procedure to post messages onto the queue, and a Get entry to read
> the next message or block if there isn't one.
>
> The spec might look like
>
>    with Ada.Containers.Vectors;
>    package Queueing is
>       type Message is new Integer;
>       package Queue_Data
>       is new Ada.Containers.Vectors (Index_Type => Natural,
>                                      Element_Type => Message);
>       protected Queue is
>          procedure Put (M : Message);
>          entry Get (M : out Message);
>       private
>          Buffer : Queue_Data.Vector;
>       end Queue;
>    end Queueing;
>
> and (as a hint) the body of the Get entry might start like
>
>       entry Get (M : out Message) when not Buffer.Is_Empty is
>       begin
>
> If your input messages are not all the same type (in Ada-speak, type
> Message is indefinite), things get more complicated; but let's cross
> that bridge only if we need to.
>
> [1]http://www.adaic.org/resources/add_content/standards/05rm/html/RM-A-1...
> [2]http://en.wikibooks.org/wiki/Ada_Programming/Tasking#Protected_types

Thank you for the reply!

Please tell me if I'm wrong:

- inside the main task I must use an accept statement "Get": by doing
it, this means that the main task wait on this "barrier" until there
is something inside the protected object queue; when entry Get is
available (due to the incoming data), the main task is automatically
notified and it executes the Get function, isnt' it? So the entry /
accept paradigm is something like events in C?
So the main task doesn't has to constantly poll the queue; the entry /
accept statement do it by itself. Am I right?

Thank everyone for the help!!!