1) The Entry's state was published after making the record avaiable,
so a thread flushing the records could see an unitialized record.
2) data_ and write_pointer_ could become out of sync. write_pointer_
could be indexing into another buffer than what data_ was pointing
to.
3) GetEntry could get a nullptr free_buffer_ because multiple threads
could acquire the work_mutex_ before the work_thread_ could wake up,
or between allocate_worker's loop iterations.
Change-Id: I6f0a015557888eeeaa75a8bce7fde8de276d11dd
Laurent Morichetti
046df32729