[Gc] segfault with CACAO on OpenSolaris

Christian Thalinger twisti at complang.tuwien.ac.at
Wed Aug 27 14:20:41 PDT 2008

On Tue, 2008-08-19 at 23:03 +0200, Christian Thalinger wrote:
> On Tue, 2008-08-19 at 20:19 +0000, Boehm, Hans wrote:
> > The CVS version contains a recent bug fix to call GC_init_thread_local
> > from GC_register_my_thread.  (See
> > http://bdwgc.cvs.sourceforge.net/bdwgc/bdwgc/pthread_support.c?r1=1.13&r2=1.14 around line 1036.)  Might this be the problem here?
> Right, that seems to fix it.  I'll test further.  Thanks so far.

I got another problem.  I think the problem is that an object is
collected although it's still in use.  I try to explain it.

When an object's lock is contended we allocate a lock record for this
object.  To clean these lock records up when the corresponding object is
collected, we register a special finalizer which is calling the Java
finalizer (if any) and freeing the lock record.

The crash I'm now seeing is like this:

LOG: [0x0000000000000003] [finalizer lockrecord: o=5d7020 p=0 class=Harness$TimeoutWatcher SYNCHRONIZED]
LOG: [0x0000000000000003] [lock_record_free  : lr=e658e0]

The object at 0x5d7020 gets collected and the lock record at 0xe658e0 is
freed.  But later another threads wakes up which is waiting on 0x5d7020
(or is trying to enter the lock, I'm not completely sure yet) and
segfaults because the lock record is not around any more:

  ---- called from signal handler with signal 11 (SIGSEGV) ------
  [16] mutex_lock_impl(0xa5a5a5a5a5a5a5a5, 0x0, 0x5d7028, 0x200, 0x2, 0x14), at 0xfffffd7fff03d580 
  [17] mutex_lock(0x0, 0x0, 0x0, 0x0, 0x0, 0x0), at 0xfffffd7fff03d70c 
  [18] Mutex::lock(this = 0xa5a5a5a5a5a5a5a5), line 127 in "mutex-posix.hpp"
  [19] Mutex_lock(mutex = 0xa5a5a5a5a5a5a5a5), line 36 in "removeme.cpp"
  [20] lock_record_enter(t = 0x462f00, lr = 0xe658e0), line 744 in "lock.c"
  [21] lock_monitor_enter(o = 0x5d7020), line 1028 in "lock.c"

So my question is, is it possible that there is a bug somewhere in the
Solaris marking code?

- twisti

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