When using pyro4 with more than 15 threads, python 2.7.12 cores frequently (>60% time)

Note "v" (op in frame 1) in frame 2 is NULL which has some value in frame 3. So some other thread cleans it.

=== gdb ===
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Core was generated by `python /etc/remoting/remoting_agent.zip run --system'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  PyDict_SetItem (op=op@entry=0x0, key=key@entry=0x7f0aa11cd420, value=value@entry=0x920ce0 <_PyExc_AttributeError.12478>) at ../Objects/dictobject.c:832

warning: Source file is more recent than executable.
832    if (!PyDict_Check(op)) {
(gdb) bt
#0  PyDict_SetItem (op=op@entry=0x0, key=key@entry='exc_type', value=value@entry=<type at remote 0x920ce0>) at ../Objects/dictobject.c:832
#1  0x0000000000529e86 in PyDict_SetItemString (item=<type at remote 0x920ce0>, key=0x61d02a "exc_type", v=0x0) at ../Objects/dictobject.c:2469
#2  PySys_SetObject (name=name@entry=0x61d02a "exc_type", v=v@entry=<type at remote 0x920ce0>) at ../Python/sysmodule.c:83
#3  0x000000000055acc0 in set_exc_info (tb=<traceback at remote 0x7f0aa1232878>, value=exceptions.AttributeError("'NoneType' object has no attribute 'SHUT_RDWR'",),
    type=<type at remote 0x920ce0>, tstate=0x95ad10) at ../Python/ceval.c:3736
#4  PyEval_EvalFrameEx (f=f@entry=Frame 0x7f0a9e929b60, for file /etc/remoting/remoting_agent.zip/Pyro4/socketutil.py, line 463, in close (self=<SocketConnection at remote 0x7f0a9e924510>),
    throwflag=throwflag@entry=0) at ../Python/ceval.c:3251
#5  0x0000000000559c27 in fast_function (nk=<optimized out>, na=<optimized out>, n=1, pp_stack=0x7ffce435ab00, func=<function at remote 0x7f0a9f6c0230>) at ../Python/ceval.c:4435
#6  call_function (oparg=<optimized out>, pp_stack=0x7ffce435ab00) at ../Python/ceval.c:4370
#7  PyEval_EvalFrameEx (f=f@entry=Frame 0x7f0a40000b50, for file /etc/remoting/remoting_agent.zip/Pyro4/socketutil.py, line 453, in __del__ (self=<SocketConnection at remote 0x7f0a9e924510>),
    throwflag=throwflag@entry=0) at ../Python/ceval.c:2987
#8  0x000000000056aa8a in PyEval_EvalCodeEx (closure=<optimized out>, defcount=<optimized out>, defs=0x0, kwcount=<optimized out>, kws=<optimized out>, argcount=1073744720, args=<optimized out>,
    locals=0x0, globals=<optimized out>, co=<optimized out>) at ../Python/ceval.c:3582
#9  function_call (func=func@entry=<function at remote 0x7f0a9f6c00c8>, arg=arg@entry=(<SocketConnection at remote 0x7f0a9e924510>,), kw=kw@entry=0x0) at ../Objects/funcobject.c:523
#10 0x00000000004be724 in PyObject_Call (kw=0x0, arg=(<SocketConnection at remote 0x7f0a9e924510>,), func=<function at remote 0x7f0a9f6c00c8>) at ../Objects/abstract.c:2546
#11 instancemethod_call.8803 (func=<function at remote 0x7f0a9f6c00c8>, arg=(<SocketConnection at remote 0x7f0a9e924510>,), kw=0x0) at ../Objects/classobject.c:2602
#12 0x00000000004c4683 in PyObject_Call (kw=0x0, arg=(), func=<instancemethod at remote 0x7f0a9f7b5b90>) at ../Objects/abstract.c:2546
#13 PyEval_CallObjectWithKeywords (kw=0x0, arg=(), func=<instancemethod at remote 0x7f0a9f7b5b90>) at ../Python/ceval.c:4219
#14 slot_tp_del.25647 (self=self@entry=<SocketConnection at remote 0x7f0a9e924510>) at ../Objects/typeobject.c:5844
#15 0x00000000004c5880 in subtype_dealloc.25650 (self=<SocketConnection at remote 0x7f0a9e924510>) at ../Objects/typeobject.c:1002
#16 0x00000000005336cf in dict_dealloc.18423 (mp=0x7f0a9e93c398) at ../Objects/dictobject.c:1040
#17 0x00000000004c56e7 in subtype_dealloc.25650 (
    self=<ClientConnectionJob(daemon=<Daemon(_Daemon__mustshutdown=<_Event(_Verbose__verbose=False, _Event__flag=True, _Event__cond=<_Condition(_Verbose__verbose=False, _Condition__lock=<thread.lock at remote 0x7f0a9f759790>, acquire=<built-in method acquire of thread.lock object at remote 0x7f0a9f759790>, _Condition__waiters=[], release=<built-in method release of thread.lock object at remote 0x7f0a9f759790>) at remote 0x7f0a9e9241d0>) at remote 0x7f0a9e924190>, objectsById={'root': <RootService(_scheduler=<Scheduler(_lock=<thread.lock at remote 0x7f0aa1211d50>, _operations={'cookie_9de0e8d93ed84452a1ce8cc92268979e': <Operation(_exception=None, _result='obj_450f0972022e41b2b7c1f29f49bdca83', _action=<function at remote 0x7f0a9f7b89b0>, _lock=<_RLock(_Verbose__verbose=False, _RLock__owner=None, _RLock__block=<thread.lock at remote 0x7f0a9f759370>, _RLock__count=0) at remote 0x7f0a9e936190>, _started_at=<float at remote 0xab90f8>, cookie='cookie_9de0e8d93ed84452a1ce8cc92268979e', _complete=<_Condition(_Condition__lock=...(truncated)) at ../Objects/typeobject.c:1035
#18 0x0000000000534b93 in frame_dealloc.14921 (f=Frame 0x7f0a9f6d49d8, for file /etc/remoting/remoting_agent.zip/Pyro4/socketserver/threadpool.py, line 39, in run ())
    at ../Objects/frameobject.c:458
#19 0x00000000004d86c6 in tb_dealloc.46270 (tb=0x7f0aa1278f38) at ../Python/traceback.c:28
#20 0x00000000004d87e1 in tb_dealloc.46270 (tb=0x7f0aa1278ea8) at ../Python/traceback.c:27
#21 0x00000000005336cf in dict_dealloc.18423 (mp=0x7f0aa1277280) at ../Objects/dictobject.c:1040
#22 0x00000000005a52db in PyInterpreterState_Clear (interp=0x95ac80) at ../Python/pystate.c:111
#23 0x0000000000423aea in Py_Finalize () at ../Python/pythonrun.c:500
#24 0x00000000004672c5 in Py_Main (argc=<optimized out>, argv=0x7ffce435b2d8) at ../Modules/main.c:665
#25 0x00007f0aa0aa7f45 in __libc_start_main (main=0x4672f4 <main>, argc=4, argv=0x7ffce435b2d8, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7ffce435b2c8)
    at libc-start.c:287
#26 0x000000000057c581 in _start ()
====


Google shows similar trace has been reported back in 2009 for python 2.6
https://bugs.launchpad.net/ubuntu/+source/system-config-printer/+bug/478071