[ECOS] MLQ scheduler policy question

[Grant Edwards <grant dot b dot edwards at gmail dot com>]

Assume we're using the MLQ scheduler and there are a set of
threads all running at the same priority.  The eCos docs
specify that the running thread won't be pre-empted by another
thread of the same priority unless the running thread
explicitly yields/blocks.

What isn't specified is what happens when a higher priority
thread becomes runnable, preempts one of our set-of-equals,
then blocks.  Since the documentation doesn't specify that the
original thread will be resumed, I assume the scheduler is free
to choose any of the ready threads?

In practice is there a way to predict which of multiple ready,
equal-priority threads will be scheduled?  [No, I'm not going
to depend on it, but I'm curious.]

The real-world case is a thread that calls send() on a TCP
socket.  Some code was written under the assumption that the
thread that called send() would continue to run (after network
threads were finished) until it explicitly yeilded or blocked.

I don't think that assumption is valid, and calling send() may
cause a context switch (indirectly) to another equal-priority
task.

-- 
Grant Edwards                   grante             Yow! We just joined the
                                  at               civil hair patrol!
                               visi.com            


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