[Mono-dev] mono crash on exits when using COM.

[tom hindle]

Bill,

Change (121114) cominterop_release_all_rcws is still in and functioning
ok.

However the problem I am seeing seems to happen before
cominterop_release_all_rcws is called from mini_cleanup.

the ccws are being freed from the finalize_domain_objects function:

#2 0x00000000004dcf2e in mono_marshal_free_ccw (object=0x7ffff4450700)
at cominterop.c:2067 
#3 0x00000000004da310 in mono_gc_run_finalize (obj=<value optimized
out>, data=<value optimized out>) at gc.c:197 
#4 0x00000000004da4c7 in finalize_domain_objects (unused=<value
optimized out>) at gc.c:984 
#5 finalizer_thread (unused=<value optimized out>) at gc.c:1039 
#6 0x0000000000500c46 in start_wrapper (data=<value optimized out>) at
threads.c:721 
#7 0x000000000059afb3 in thread_start_routine (args=0x987a50) at
wthreads.c:286 
#8 0x00000000005c0d0f in GC_start_routine (arg=0x7ffff7e88e70)

before cominterop_release_all_rcws is called.

Also I can only seem to reproduce the fault in a NUnit test. The
identical code in a main block doesn't seem to show the error.

I'm wondering if it has anything to do with Application domain's? 

Thanks,
Tom

On Sat, 2010-01-23 at 12:48 -0500, Bill Holmes wrote:
> Tom,
> 
> I beleive that we had a problem with this before and I applied a fix.
> http://anonsvn.mono-project.com/viewvc?view=revision&revision=121114
> 
> IIRC this code/fix should release all outstanding rcws before the
> final collect of other mono objects, including ccws.
> 
> Can you investigate if this change (121114) has been broken, or needs enhanced?
> 
> -bill
> 
> On Fri, Jan 22, 2010 at 8:26 PM, tom hindle <tom_hindle at sil.org> wrote:
> >
> > I have added a check in mono_gc_run_finalize (void *obj, void *data)
> > (gc.c):
> >
> > ---
> >
> > if (suspend_finalizers)
> >                return;
> >
> > + if (mono_marshal_ccw_refcount(o) > 0)
> > + {
> > +  return;
> > + }
> >
> > domain = o->vtable->domain;
> >
> > ----
> >
> > This seems to solve the problem. The ccw isn't freed, which means when
> > the rcw releases its reference to the ccw, so it no longer segv's.
> >
> > Does this seem like an valid approach? I'm not sure If this means that
> > finalize_domain_objects needs to make multiple passes at freeing the
> > ccw's? I guess this change would also mean the badly written native COM
> > objects would prevent ccw from being freed. Is this a problem?
> >
> > Thanks
> > Tom
> >
> >
> > On Fri, 2010-01-22 at 16:16 -0700, tom hindle wrote:
> > > Hi all,
> > >
> > > I have been investigating some seemingly random crash on exit problems
> > > that our application has been having.
> > >
> > > I have managed mostly reliably to reproduce the issue by following this
> > > set of steps:
> > >
> > > 1. Create a managed object ManagedObj
> > > 2. Create a COM object COMObj for which its rcw is likely to be Garbage
> > > collected after ManagedObj and during mono shutdown.
> > > 3. Make COMObj contain a ref to ManagedObj's ccw
> > > 4. Set ManagedObj ref to null
> > > 5. Call GC.Collect() to encourage GC.
> > >
> > > If Garbage Collection of COMObj's rcw happens after the Garbage
> > > Collection of ManagedObj's ccw, then when COMObj calls Release on its
> > > ref to ManagedObj's ccw a segv is produced.
> > >
> > > Normally it seems that ref counts for the wrappers are respected,
> > > however this doesn't seem to be the case on program shutdown.
> > >
> > > Some pseudo code which reproduces the problem:
> > >
> > > public class TestComRelease
> > > {
> > > static COMObj cObj;
> > >
> > > [Test]
> > > public void Test()
> > > {
> > >    ManagedObj mObj = new ManagedObj()
> > >    cObj = new COMObj();
> > >    cObj.SetManagedRef(mObj);
> > >    mObj = null;
> > >    GC.Collect();
> > > }
> > >
> > > }
> > >
> > > I am attempting to find the cause of this in mono. Any pointers would be
> > > grateful received.
> > >
> > > Thanks
> > > Tom
> > >
> > > _______________________________________________
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> > > Mono-devel-list at lists.ximian.com
> > > http://lists.ximian.com/mailman/listinfo/mono-devel-list
> >
> >
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