Ordinarily when getPooledConnection() is called it will lock the connections
map (0x00000000861e8e18) and then perform a Connections.get() on an
individual Connections object. Since Connections.get() is synchronised, this
Connections object is locked.
In parallel to this the PoolCleaner thread may call cleanup() which in turn
calls Pool.expire(). This call grabs a lock to the connections map
(0x00000000861e8e18) and then attempts to run Connections.expire() on an
individual Connections object.
Unfortunately in this instance the PoolCleaner thread is grabbing the
connections map (0x00000000861e8e18) before getPooledConnection() can lock
it, but *after* our thread has locked the Connections object
(0x000000008b0c96d0) in the previous recursive set of calls.
The situation is complicated by both the recursion and the fact that we
are locking on a different Connections object than we had been
previously in the stack.