Attempts to promote all objects from generation zero into generation one, thereby clearing generation zero.
This is useful when passing from a phase of creating long-lived data to a phase of mostly ephemeral data, for example, the end of loading an application and the start of its use.
It may be more efficient to directly allocate the objects in a particular generation in the first place, using allocation-in-gen-num or set-default-generation.
allocation-in-gen-num collect-generation-2 collect-highest-generation expand-generation-1 set-promotion-count