(gdb) thread apply all bt
Thread 2 (process 76664):
WT-3  0x000000010f3f6512 in __wt_abort (session=0x7feee7816000) at os_abort.c:21
WT-4  0x000000010f423bf4 in __wt_assert (session=0x7feee7816000, error=0, file_name=0x10f43fed2 "../src/session/session_api.c", line_number=838, fmt=0x10f436528 "%s") at err.c:452
WT-5  0x000000010f41f693 in __wt_open_session (conn=0x7feee7802000, event_handler=0x0, config=0x0, sessionp=0x10f900e40) at session_api.c:838
WT-6  0x000000010f41f4bb in __wt_open_internal_session (conn=0x7feee7802000, name=0x10f43c771 "cache-pool", uses_dhandles=0, open_metadata=0, sessionp=0x7feee3654b78) at session_api.c:758
WT-7  0x000000010f3a65d2 in __cache_pool_balance () at conn_cache_pool.c:353
WT-8  0x000000010f3a6ecc in __wt_cache_pool_server (arg=0x0) at conn_cache_pool.c:542

Thread 1 (process 76664):
#0  0x00007fff8d3aa122 in __psynch_mutexwait ()
WT-1  0x00007fff8e2dcdfd in pthread_mutex_lock ()
WT-2  0x000000010f41aefc in __wt_spin_lock (session=0x7feee7816280, t=0x7feee7802300) at mutex.i:172
WT-3  0x000000010f41abbd in __session_close (wt_session=0x7feee7816280, config=0x0) at session_api.c:119
WT-4  0x000000010f351605 in __wt_evict_destroy (conn=0x7feee7802000) at bt_evict.c:329
WT-5  0x000000010f3aba58 in __wt_connection_close (conn=0x7feee7802000) at conn_open.c:151
WT-6  0x000000010f3a18d3 in __conn_close (wt_conn=0x7feee7802000, config=0x0) at conn_api.c:614
WT-7  0x000000010f30ed9d in _wrap_Connection_close (self=<value temporarily unavailable, due to optimizations>, args=<value temporarily unavailable, due to optimizations>) at ../../../lang/python/wiredtiger_wrap.c:7148

        /*
         * Make sure we don't try to open a new session after the application
         * closes the connection.  This is particularly intended to catch
         * cases where server threads open sessions.
         */
        WT_ASSERT(session, F_ISSET(conn, WT_CONN_SERVER_RUN));