fix cond_race... was RE: src/winsup/cygwin ChangeLog thread.h ...

Jason Tishler
Sun Oct 21 19:15:00 GMT 2001


On Mon, Oct 22, 2001 at 11:54:39AM +1000, Robert Collins wrote:
> Of course, if python doesn't set thread priority then 3 is unlikely.

I don't know, but I found the following tidbit while grep-ing the Python
code for "priority":

        // Using Sleep(0) can cause a priority inversion.
        // Sleep(0) only yields the processor if there's
        // another thread of the same priority that's
        // ready to run.  If a high-priority thread is
        // trying to acquire the lock, which is held by
        // a low-priority thread, then the low-priority
        // thread may never get scheduled and hence never
        // free the lock.  NT attempts to avoid priority
        // inversions by temporarily boosting the priority
        // of low-priority runnable threads, but the problem
        // can still occur if there's a medium-priority
        // thread that's always runnable.  If Sleep(1) is used,
        // then the thread unconditionally yields the CPU.  We
        // only do this for the second and subsequent even
        // iterations, since a millisecond is a long time to wait
        // if the thread can be scheduled in again sooner
        // (~100,000 instructions).
        // Avoid priority inversion: 0, 1, 0, 1,...

The above seems to resonant with your possibility #3.


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