Re: Cyg_Mutex::check_this() fails

[jamescmaki <jamescmaki@gmail.com>]

Hi Rene,

At this point in the code the scheduler is not locked and the mutex is not
owned. This means that it is a bad idea to be looking at the internal state
of the mutex, i.e., calling CYG_ASSERTCLASS( mx, "Corrupt mutex").

I can reproduce this issue consistently now and I am testing a fix that
changes CYG_ASSERTCLASS to CYG_ASSERT. I am hoping that this will resolve
the problem instead of just moving the failed assert into Cyg_Mutex::lock().

However even if this does fix the problem, I am still wary. From what I can
see, locked and owner are never modified without locking the scheduler. This
means that they are both updated atomically. Because of this, when the
thread in  wait_inner() resumes it should see both of these variables in a
consistent state regardless of whether it holds a lock or not. I am
wondering if this can be explained by reordering and by delaying the check
until the scheduler is locked again it avoids this problem.

-James





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