Memoize a variable that could change by a separate thread. (#1081)
Memoize a variable that could change by a separate thread. (#1081)

https://jira.mongodb.org/browse/RUBY-1507?filter=26037&jql=status%20%3D
mongodb/mongo-ruby-driver,mongodb/mongo-ruby-driver,mongodb/mongo-ruby-driver,jonhyman/mongo-ruby-driver,saghm/mongo-ruby-driver,jonhyman/mongo-ruby-driver,saghm/mongo-ruby-driver