When the first task is queued, I trigger a callback so the UI can start
processing when idle. I return the size of the queue from both
run_task() and queue_task() so the UI knows when to stop processing
callbacks.
I don't actually perform a library update at this point, but I do create
a new task and add it to the update queue. When the run_task() function
is called, the task is removed from the queue and deleted.
