Re: Structure of the multitasking server

[Brad Moore <brad.moore@shaw.ca>]

On 15-03-15 03:21 AM, Jacob Sparre Andersen wrote:
> J-P. Rosen wrote:
>
>> If you give the producer a lower priority than the workers, it will be
>> activated only when workers are done, and busy waiting is no more a
>> problem.

I use this approach in the Ravenscar Paraffin libraries.

Note though, that this approach only works on real-time systems, which implement the priority model.

Linux (and Windows) for example by default doesn't do this, so the spinning of the lower priority task can interfere
with the higher priority tasks running on the same core. If you are using a flavor of Linux that has been configured for
real-time then you should be able to rely on this behaviour.

   See
     https://rt.wiki.kernel.org/index.php/RT_PREEMPT_HOWTO#About_the_RT-Preempt_Patch

Otherwise, this approach doesn't really work (it works but inefficient because CPU is wasted on spinning),
so you should use blocking instead of spin waiting.
In Paraffin, I provide two versions of Ravenscar libraries (one blocking, and one spinning), so that you can use
whichever version best suits your OS.

Brad

>
> Nice solution. :-)
>
> Greetings,
>
> Jacob
>