Re: RFC: Prototype for a user threading library in Ada

[Hadrien Grasland <hadrien.grasland@gmail.com>]

Le samedi 18 juin 2016 13:53:13 UTC+2, Dmitry A. Kazakov a écrit :
> On 2016-06-18 11:17, Hadrien Grasland wrote:
> 
> > But nonblocking IO is something I want to study more during the
> > evolution of this library, as I think it is something which stresses the
> > limits of the event model I propose. Single-shot events are a good fit
> > when a clear notion of task completion exists, but they are less
> > suitable when dealing with continuous processes such as streaming IO.
> 
> You could use a pulse event instead. The event is reset when all waiting 
> tasks are released. It is not difficult to implement with protected 
> objects using entry count attribute.

I am not very keen on this option because if is incompatible with state polling, which is useful for all kinds of non-waiting scenarios including component testing ("what is the state of my event after performing this operation?").

 
> > I do not want to go in the direction of reusable events, as the
> > amount  of ways these can go wrong is all but infinite, however there has to be
> a better synchronization primitive for this kind of progressive evolution.
> 
> One solution is to have more states than Reset/Signaled. An event can 
> traverse a larger set of states being a small state machine. As well as 
> transitions may be initiated not only explicitly but also through 
> scheduling events, e.g. task release in case of the pulse event.

Would you mean something like, for example, a discrete or floating-point progress counter that can be programmed to fire an event when going above any arbitrary level of progress?

That could be a very interesting avenue to explore indeed!