Exclusive Table Lock

Hello!

How would I get a lock on an entire Postgres table, such that no other process can update any row in the table (but can still read rows with SELECT)?
I think the lock type I want is EXCLUSIVE, but I am not sure how do acquire such a lock for the entire table using an Ecto query.

Thanks!

I asked the question in Stack Overflow as well: https://stackoverflow.com/questions/54243741/how-to-get-an-exclusive-lock-on-a-postgres-table-using-ecto