Looking back at this patch, I think we can extract the thread-synchronization parts and the peek() method, as they're both valuable additions, especially the first one.

The very sched doc says:

> In multi-threaded environments, the scheduler class has limitations 
> with respect to thread-safety, inability to insert a new task before 
> the one currently pending in a running scheduler, and holding up the 
> main thread until the event queue is empty. Instead, the preferred 
> approach is to use the threading.Timer class instead.