Re: [LAD] memory allocation for the real time thread, opinions wanted

On Mon, 27 Feb 2012 20:01:18 -0500
Paul Coccoli <pcoccoli@email-addr-hidden> wrote:

> On Mon, Feb 27, 2012 at 8:04 AM, Fons Adriaensen
> <fons@email-addr-hidden> wrote:
> > On Mon, Feb 27, 2012 at 09:59:19AM +0100, Nick Copeland wrote:
> >
> >> Both of these methods are affectively the same, what you are
> >> trying to do is provide a method that the low prio thread is
> >> responsible for both malloc and free.
> >
> > That's a nice method, it effectively uses the LFQ to 'send back' an
> > item after use by the recipient. It depends on the particular
> > implementation of the queue, you need one that allows to read one
> > (or more if necessary) items without moving the read pointer - that
> > should be done only after the data has been used since it signals
> > that the data can be freed.
> >
> > The alternative is to make this explicit, by having two pairs of
> > indices operate on the same buffer:
> [SNIP]
>
> Why not just use 2 ringbuffers: one to send pointers to the RT thread,
> and a second to send them back to the low prio thread (so it can free
> them). You probably need a semaphore for the return ringbuffer, but
> that should be RT-safe.

That's what I thought... would be better for someone who is new to real
time threads and memory allocation... and is what I decided on... minus
the semaphore.

So why is a semaphore needed? If the RT thread only sends an item back
when it absolutely no longer will use it?

James.

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