Re: Private or public task ?

["Alex R. Mosteo" <alejandro@mosteo.com>]

Maciej Sobczak wrote:

> On 5 Lut, 22:53, Hibou57 (Yannick Duchêne) <yannick_duch...@yahoo.fr>
> wrote:
> 
>> I did not ever suspected such a requirement. Transitive blocking is
>> not allowed ?
> 
> As far as I understand, there is a careful wording around this subject
> so that formally speaking protected operations (except for entries)
> are not themselves "blocking". So, for example, you can call protected
> operations from other protected operations.

And this makes sense: if you don't allow anything blocking inside a 
protected procedure, it follows that the procedure is itself non-blocking :)

Entries, on the other hand, are blocking... because you don't know if you'll 
be blocked on the entry conditional. This is true even for non-conditional 
entries, I think, because of possible requeues.

Alex.

> The operations that are considered to be blocking in this context are
> delay statements, entry calls, select statements and... I/O
> operations. These cannot be called from protected operations.
> 
> (I'm sure somebody will correct me if I'm off tracks)
> 
>> So, if blocking operation are not allowed from a protected type,
>> clients of a given operation have to know it weither or not it's
>> potentially blocking,
> 
> That would be nice, yes. But be careful, this approach might blow up
> the language. What about exception specifications? And so on.
> 
> But: see RavenSPARK.
> 
> The problem with blocking in particular is that there is no way to
> verify whether imported subprograms (from C libraries, for example)
> are blocking. You can import I/O operations from C libraries and there
> is no way to verify what they do.
> 
> --
> Maciej Sobczak * www.msobczak.com * www.inspirel.com
> 
> Database Access Library for Ada: www.inspirel.com/soci-ada