libpthread patch

Daniel Eischen eischen at pcnet1.pcnet.com
Wed Apr 16 16:46:05 PDT 2003


On Thu, 17 Apr 2003, David Xu wrote:

> 
> ----- Original Message ----- 
> From: "Daniel Eischen" <eischen at pcnet1.pcnet.com>
> To: "David Xu" <davidxu at freebsd.org>
> Cc: <freebsd-threads at freebsd.org>
> Sent: Thursday, April 17, 2003 5:05 AM
> Subject: Re: libpthread patch
> 
> 
> > There's a new patch available at:
> > 
> >     http://people.freebsd.org/~deischen/kse/libpthread.diffs
> > 
> > This passes all the ACE tests that libc_r passes, with the
> > exception of Cached_Conn_Test.
> > 
> > It also seems to work with KDE, konqueror, kwrite, kmail, etc.
> > I don't have mozilla built (and am dreading trying to), but
> > it would be interesting to see if it works with that.
> > 
> 
> Cool!
> 
> > If no-one has any objections, I'd like to commit this
> > soon.  I'll let David review and comment to it first.
> > 
> > David, I didn't add critical regions to _thr_alloc() and
> > _thr_free().  I think that whenever they are used, we
> > are already in a critical region or operating on an upcall.
> > 
> 
> Hmm,  I don't like to put malloc calling under critical section,
> it is better to put it under a lock, otherwise this would cause dead 
> lock. suppose that an user thread is calling malloc(), and heap manager
> got malloc spinlock, then it does somethings and the thread is preempted
> by upcall from kernel,  now UTS switches to another thread, that thread
> starts to call  pthread_create,  so UTS kernel enters a critical region first,
> and calls malloc, this would cause dead lock, because UTS is under critical
> region and no context switch could happen.

Hmm, I see what you mean.  We could put spinlock in critical region
and that may solve the problem, but I eventually want to see spinlocks
go away and replace the very few that we have in libc with mutexes.

> Also I don't like thr_free under critical region, I think a GC thread is still
> needed to recycle zombie thread and free extra memory, UTS kernel 
> should't be blocked by user thread. Despite this,  I think the patch should
> be committed. 

I'll work on adding the GC thread back in.  I really wanted to
get rid of it so that the KSE can exit when threadcount == 0,
but now we've got to make allowances for the extra thread
in the main KSEG.

Keep looking at the patch for anything else you might see.
We still need a way to deliver signals and look for async
cancel points in CPU-bound threads.  The attempt to add a
signal frame with signalcontext() doesn't seem to work
which is why it is commented out.

-- 
Dan Eischen



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