[Boost-users] [Lockfree] spsc example query

Hi, I'm just about to start using the spsc queue in a project and whilst reading the example at: https://www.boost.org/doc/libs/1_74_0/doc/html/lockfree/examples.html#lockfr... looking at the consumer function, there appears to be two while loops retrieving items from the queue inside the outer loop that checks whether the done variable is true. Can somebody please explain why this is, or, is it a bug in the example? I would have thought one inner while loop would be enough. Thanks, Sean.