[Gc] Race condition between thread termination and garbage collection under Solaris 10/x86

Boehm, Hans hans.boehm at hp.com
Fri Mar 5 18:16:36 PST 2010


Thanks.

I'm nervous about applying something along these lines.  We would end up with a bunch of duplicated code.  And I think this introduces some more races, e.g. between threads accessing the thread table while holding the allocation lock, and those accessing it while holding the "solaris threads lock".  I also don't think the allocation lock is a pthread_mutex in all configurations.  (Check USE_SPIN_LOCK)  And I don't think it handles the case of a thread acquiring the allocation lock in a cleanup handler for other reasons.

If we want to do something like this, I'd intercept pthread_exit() and pthread_cancel() like the other pthread primitives, have them set a flag in the appropriate thread structure (with the allocation lock held), and have a stop_world attempt loop until it sees a thread table with none of those bits set.  (In the case of pthread_exit() we don't need to do anything if the thread structure is already gone, I think.)

I wish I understood the problem completely.  I looked a little more on Linux.  Although the deadlock actually seems similar, I didn't seen any blocked signals.  I think that avoids further correctness issues, though it may have performance or even termination problems.

I'll bet at the C++ standards meeting next week, where I should at least be able to find a Posix expert ...

Hans

> -----Original Message-----
> From: gc-bounces at napali.hpl.hp.com 
> [mailto:gc-bounces at napali.hpl.hp.com] On Behalf Of Burkhard Linke
> Sent: Thursday, March 04, 2010 11:41 AM
> To: gc at napali.hpl.hp.com
> Subject: Re: [Gc] Race condition between thread termination 
> and garbage collection under Solaris 10/x86
> 
> Hi,
> 
> the former patch introduces a race condition if several 
> threads are terminating at the same time (Acquring allocator 
> lock while holding thread lock). Revised patch is attached.
> 
> Burkhard
> 


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