Re: AW: [ECOS] Blocking restricted in DSRs

[Nick Garnett <nickg at ecoscentric dot com>]

"Neundorf, Alexander" <Alexander.Neundorf@jenoptik.com> writes:

> ...
> > Threads can call blocking functions with the scheduler locked. The
> > lock is essentially a per-thread variable so when the thread is
> > resumed the lock is returned to its former value.
> 
> IOW cyg_scheduler_lock() ensures that the scheduler doesn't run as
> long as the thread which called cyg_scheduler_lock() doesn't call a
> synchronization function which calls itself the scheduler, right ?
>

Correct.

> But still I don't understand the code.  cyg_scheduler_lock() calls
> Cyg_Scheduler::lock() in sched.inl, which calls
> inc_sched_lock(). This I find in smp.hxx. I don't see any thread
> specific data there, so how can this act thread-specific ?

The next lock value is passed as an argument to unlock_inner() and is
therefore saved across the context switch on the stack and set when
then thread is rescheduled. That is why I said "essentially", since it
is not stored explicitly in the thread object.

-- 
Nick Garnett                    eCos Kernel Architect
http://www.ecoscentric.com/     The eCos and RedBoot experts


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