[cpp-threads] Asynchronous Execution Issues

[Peter Dimov]

Boehm, Hans:
> I'm starting to have second thoughts about non-trivial destructors for 
> thread_locals ...

Without destructors, we'll have to either leak the thread-local objects 
(such as free lists and per-thread extra state) or go back to using 
pthreads. It's OK to leak on process exit, but not on thread exit (which is 
why I think that the C++0x exit() order is wrong and the pthreads one is 
right).