[Tinyos Core WG] TOSThreads TEP

[Vlado Handziski]

Thanks for posting this Kevin. I think it is very important that we have a
high quality technical documentation to support us in discussing the
proposal. That's why I suggested that writing a proper TEP would be very
helpful. I like to congratulate you on the great effort. Please take my
comments below not as critique on the your design or implementation, but as
an attempt to start a more high level discussion on the direction we want to
see TinyOS go, before plunging in the technical details about the actual
proposal. I sounded most of my concerns directly with you after the
presentation here at TUB, but now that we have an official proposal, I would
like to voice some of them on this forum too.

I think that the name of the TEP is misleading. What is on the table here is
much more then a simple threading library. This is not a simple "add on",
but a fundamental redefinition of the basic premises of the OS. You are not
proposing a threading add on to TinyOS, you are proposing a new thread-based
OS that wants to run TinyOS as a kernel thread.

The component-based model combined with the even-driven nature and the two
concurrency classes have defined what TinyOS means ever since the "System
Architecture Directions" paper. TinyOS never tried to be everything to
everyone, it was designed based on a specific set of assumptions about what
is important in the (mote-class) networked embedded systems. We all know
that this simplicity has its price. The split-phase model, having to keep
eye on the duration of the tasks, etc. It is true that the TinyOS model is
sometimes very hard for the new users to grok. It is also true that in some
situations it is hard to naturally decompose the processing in short task
chunks (crypto routines, etc.).

I understand that threading is seen by many as the natural solution for
these problems, people coming from the PC world are used to them, they allow
programmers to forget about concurrency, etc. I think that they just give a
false sense of simplicity, but I can see how people might want to use them
with TinyOS also. Many papers have been written on this, yours is the latest
one, so clearly there is some push to go in this direction. But if we start
walking down that path, where do we stop? After matching the features of
Mantis OS and SOS, what's next? Making TinyOS a general purpose OS?

I for one, still believe in the basic soundness of the event-driven model
even for user/app code. In this sense, I personally have a problem with a
threading solution that is not completely optional. I don't want to have a
thread scheduler being run by default. I don't want to pay a price for
wakeupThread on every interrupt. With all of those things by default in, for
me this would not be TinyOS anymore.

Vlado


On Tue, May 20, 2008 at 9:34 AM, Kevin Klues <klueska at gmail.com> wrote:

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