raid1_conf_t member meanings

Hi,

I'm reading the source codes of RAID1. In file 
'include/linux/raid/raid1.h',
in struct raid1_private_data, there are these members:

unsigned long start_active, start_ready, start_pending, start_future;
int cnt_done, cnt_active, cnt_ready, cnt_pending, cnt_future;

Could anybody tell me the meaning of 'active, ready, pending, future' 
and
'cnt_done'?

Thanks a lot.
Bin