lep: request all the things

I thought it was an implementation detail, but maybe it's worth mentioning. The loop keeps track of active requests using a queue, so we cannot really insert anything there from another thread. My idea was to have a separate queue for callback requests which are sent from a different thread, then, as part of the loop processing, those requests are fully initialized and added to the normal queue. This other queue would need to be thread safe, using locking, atomic ops or whatever.