boost::shared_mutex vs boost::mutex for multiple threads writing?

boost::shared_mutex vs boost::mutex for multiple threads writing?

I have a scenario where multiple threads are writing to a common buffer (a
map), each thread could or could not have the same key. Can someone please
advise on whether i should use boost::shared_mutex or just boost::mutex?
My understanding is that boost::shared_mutex is for a single writer and
multiple reads which is not what i want. Does this make boost::mutex more
appropriate for this scenario?
thanks in advance