Thanks for clarification! I'll be able to test the patch in a couple of days.
- MB. Respectfully On Thu, Sep 27, 2018 at 01:49:23AM -0400, Mark H Weaver wrote: > Hi, > > Thanks for the additional details. I was able to reproduce the bug, and > I believe I now see the problem. > > 'atomic-box-compare-and-swap!' is implemented using > 'atomic_compare_exchange_weak' (if available), but neglects to handle > the case where 'atomic_compare_exchange_weak' may spuriously fail. In > that case, the box is left unchanged, although the observed value was > equal to the expected value. > > What's happening here is that the 'atomic-box-compare-and-swap!' in > 'sleep-loop' fails spuriously, leaving the box in state #:accepted > although it returns #:accepted as its result. When the main loop > discovers this, it changes the state to #:need-to-sleep, although the > thread has already ended. > > To confirm this hypothesis, I added a print statement to the main loop > showing the state of the box that it observed during the protocol > exchange, and indeed it sees #:accepted the first time it checks, and > #:need-to-sleep in all later iterations. > > I've attached a proposed patch that I hope will fix this problem. If > you'd be willing to test it, I'd be grateful, but otherwise I'll try to > test it in the next week or so. My access to armv7l boxes is somewhat > limited. > > Thanks for this report. > > Mark > >
