Re: Launching background job from Ada.Real_Time.Timing_Events

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 24/05/2016 16:22, Alejandro R. Mosteo wrote:

> I'm stuck with something not that strange, so I guess I need another
> viewpoint on it.
>
> I want to trigger, in the future, a possibly long computation in the
> background. For that I had thought of using the built-in Real_Time events.
>
> My idea was to queue the job when the event is triggered, and to have a
> worker thread waiting for jobs in the queue. However, I've just realized
> that the event handler is itself a protected action, so I can't call
> another potentially blocking enqueue from there.

Neither is protected action. To enqueue anything into FIFO you need no 
locking. This is lock-free. To dequeue, provided single consumer there 
is no need to lock anything either. If there are several consumers, you 
use a protected object to dequeue only.

1-to-n: The dequeue is a waitable entry. Once you have got the packet 
out of the queue you process it outside any protected actions.

1-to-1: You use a reset-event implemented using protected object to wake 
up the consumer, which dequeues the packet. Reset event is 
race-condition free to query if the queue is empty and if so, to wait 
for the event.

> Any ideas? Basically, how to trigger another task (without creating it)
> from within a protected handler?

Always by waiting for an entry. E.g. as described above.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de