[En-Nut-Discussion] Feature Request 1572837: mutex API nesting level info

[Nathan Moore]

On Tue, Jul 22, 2008 at 12:58 PM, Bernard Fouché <bernard.fouche at kuantic.com>
wrote:

> Nathan Moore wrote:
> > Well that's exactly what they are good for.  You have not told me why
> they
> > are bad, only
> > that I'm doing stuff wrong.  I don't see anything wrong with using a
> > recursive mutex.
> >
>
> That's exactly the point: they are bad because they encourage you to do
> wrong stuff! Without recursive mutexes you would have reconsidered your
> design and discovered that you can live without them. However for quick
> prototyping they may be handy but then you have to work twice on the
> same code, once for writing the prototype, once to finalize the design.


I can live without lots of things.  I can live without a compiler if I have
to.
I can live without a text editor and just do
   $ cat > source.c
   #include ...

but that's not something I do very regularly.



>
> > Ok, implement a splice with your method.
> > I want to take stuff from Uart1 and output it to Uart2 up until an IO
> line
> > goes low.
> > When that happens I want Uart1 to be used by other threads to output any
> > status
>
CORRECTION -- ... I want Uart2 to be used by other threads to ...

>
> > messages that they may have until that IO line goes high again (which
> will
> > likely
> > cause an interrupt which will post an event).
> >
> >
>
> I think that unless real code is written like you did in your first
> example, it's difficult to provide a good answer:  in this second
> problem description, there is no specification forbidding to always
> allow threads to output to UART1, even if UART1's input is to be output
> on UART2 according to the IO line (there is also nothing in your
> description about what to do with UART1's input when the IO line changes
> of state and threads are outputing to UART1). Maybe no mutex is needed
> at all.

Sorry about the mistake in my example.

>
>
> Note that such a splice can be difficult: if the IO line drives the
> application behavior regarding UART's, you may reach a situation where
> the IO line changes of state but there is already a character placed in
> a UART register (rx and/or tx). So you may send/receive unexpected
> characters on a UART, just after the IO line state change. (This problem
> is not mutex related at all)

It doesn't have to be perfect, just keep messages together.  If a status
message
is being output it should be output completely and contiguously.


>
>
> Maybe multiplexing would be a better solution? This would allow you to
> specify what is the final usage of a character and helps the remote
> party not to badly mix received characters.

I do not understand this.  The second sentence doesn't make sense.

Nathan