BRPOPLPUSH is the blocking variant of RPOPLPUSH.
When source contains elements, this command behaves exactly like RPOPLPUSH.
When used inside a MULTI/EXEC block, this command behaves exactly like RPOPLPUSH.
When source is empty, Redis will block the connection until another client
pushes to it or until timeout is reached.
A timeout of zero can be used to block indefinitely.
See RPOPLPUSH for more information.
*Return value
Bulk string reply: the element being popped from source and pushed to destination.
If timeout is reached, a Null reply is returned.
*Pattern: Reliable queue
Please see the pattern description in the RPOPLPUSH documentation.
*Pattern: Circular list
Please see the pattern description in the RPOPLPUSH documentation.