timerfd deadlock

Ken Brown kbrown@cornell.edu
Mon Jun 24 20:16:00 GMT 2019

On 6/11/2019 4:52 AM, Corinna Vinschen wrote:
> On Jun  7 12:10, Ken Brown wrote:
>> While testing some new pipe code, I'm occasionally seeing a timerfd deadlock:
>> The main thread is stuck in timerfd_tracker::dtor at timerfd.cc:354, waiting for
>> the timerfd thread to close; and the timerfd thread is stuck at timerfd.cc:140,
>> waiting to acquire a mutex that's held by timerfd_tracker::dtor.
> Hmm, I had hoped my current code does not have a deadlock situation
> anymore, but I was wrong, apparently.
> Is there any chance to create an STC?

I haven't been able to create an STC.  The deadlock seems to depend on a rare 
timing fluke, and I've only seen it when running a parallel make on a clean 
emacs tree, with my new pipe code installed.

On the other hand, I think I have a simple fix, which I'll send to 
cygwin-patches.  With this patch, I ran the parallel make 15 times without 
getting the deadlock.  After reverting the patch, I got the deadlock on the 4th run.


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