Scheduler - Abstract base class for schedulers.
Abstract base class for schedulers. Should not be instantiated directly.
Should never be called; subclasses should override.
get_next_unique should return the next scheduled item, according to whatever scheduling scheme the subclass implements. The same item should *not* be returned more than once between calls to reset_available.
If there are items in the scheduler that have not already been dispensed since the last call to 'reset_available', next_available should return the minimum amount of time (in floating seconds) until one of them might become available.
If there will never be any such items available, it should return -1.
In Geo::Coder::Many, next_available is used to tell the result-picker whether it is worth waiting for more results.
This is called in order to indicate that all items should once more be made available.
This is called to provide information about the performance of a geocoder. Does nothing by default.