将来完成时用来表示在将来某一时间以前已经完成或一直持续的动作。经常与before+将来时间或by+将来时间连用，也可与before或by the time引导的现在时的从句连用。
过去完成进行时由“will / shall have been+现在分词(doing)”构成，通常还会有其他状语成分表示时间长短。
She will have been having treatment all her life.
By the end of next month he will have been here for ten years.
By this time next year, we will have been doing business with each other for 20 years.
By the end of this year he’ll have been acting for thirty years.
By the end of this month he will have been training horses for twenty years.
By the end of this month he will have been climbing mountains for twenty years.
Before turning into 42, Tom will have been jogging for 10 years.