Re: Ada.Text_IO and protected objects

[Jacob Sparre Andersen <sparre@nbi.dk>]

Fabio de Francesco wrote:

> Thank you all for every insight on the subject. Anyway I don't yet
> understand whether you mean that potentially "blocking" subprograms
> should be put in a protected object or inversely they shouldn't.

"Potentially blocking" subprograms should not be called from
procedures, functions and entries of protected objects ("protected
actions").

> In this thread I've been suggested to put the IO in a protected
> object.  Is it needed to do so?

It is wrong to do so. - I apologise for the misleading advise.

IO has to be done from a task (optionally the main task), not from
inside a protected action.

I am not sure if the appropriate way of handling access to
Standard_Output is by using a protected object to manage a queue for
transferring data to the task doing the actual writing to
Standard_Output, or if the interaction should be through a direct
rendezvous with the task doing the actual writing to Standard_Output.

There is a "dining philosophers" example available somewhere on the
web (written by Feldman, I think), where you probably can find a good
example of how to solve the combination of tasking and IO.

> What do you mean by "blocking"? I suppose you mean that OS can put
> that process in a wait queue and switch to a new one, may be because
> the first is waiting for some event like device IO. Is it correct?

I think that is correct, but hopefully somebody more experienced in
tasking will answer the question.

Ciao,

Jacob
-- 
"If you think Tuck has said something that is completely
 wrong, you are almost certainly missing something :-)"