A Future_PG is an instance which represents a promise of information
at some point in the future. Any use of the accessors of a Future_PG
will block until the properties are actually available.
An LDM plugin may initially supply a Future_PG of the appropriate class
rather than a real PG in order to back-fill later.
Method Summary
void
finalize(PropertyGroup realPG) Indicate to anyone blocked on the accessors of the Future
that the real values are available.