Maps a block's parent to the threshold state for the following period.
Declared in <versionbits.h>
typedef std::map<CBlockIndex const*, ThresholdState> ThresholdConditionCache;The state applies to blocks whose height is a multiple of Period(). The map is indexed by the block's parent, however, so all keys will either be nullptr or a block with (height + 1) % Period() == 0.