Re: [Sbcl-devel] Can make (get-universal-time) to hang

[Max M. <ma...@op...>]

At Tue, 28 May 2013 18:23:54 -0400,
Max Mikhanosha wrote:
> 
> I have a test case, where by killing lots of threads, that use
> %without-interrupts/with-interrupts to try to manage their cleanup, I
> can somehow get SBCL into the state where
> 
> 1. (decode-universal-time (get-universal-time))
>    ;; hangs the calling thread, interrupting
>    ;; shows single "bogus frame"
> 
> 2. (decode-universal-time (get-universal-time) 0)
>    ;; works fine
> 

I have traced it to localtime_r() hanging.. My understanding of this is as follows:

localtime_r() uses locking on some mutex, that checks if tzset() been called since
last time it cached the timezone info

If a Lisp thread gets killed while its doing localtime_r() in the
foreign code, that mutex or whatever its using is stuck, and any
farther localtime_r() from the same process hang.. This actually has
very devastating consequences for SBCL, as it shuts down the compiler,
because it uses decode-universal-time.

The test case to reproduce it, would be to repeatedly start and stop
many threads, that call (decode-universal-time) without time-zone
argument.

The fix would be to block signals around calls to localtime_r and gmtime_r

Regards,
  Max