1389
1369
data during reads, and allows a 'write_group' to be obtained. Write
1390
1370
groups must be used for actual data insertion.
1398
1372
:param token: if this is already locked, then lock_write will fail
1399
1373
unless the token matches the existing lock.
1400
1374
:returns: a token if this instance supports tokens, otherwise None.