lock a group of keys
int tdb_chainlock(TDB_CONTEXT *tdb, TDB_DATA key);void tdb_chainunlock(TDB_CONTEXT *tdb, TDB_DATA key);
is a low-level function used to lock a particular key (and a number of
other keys) without any checking: any other process attempting to
perform tdb operations on those keys will block until
It is the user's responsibility to ensure that they do not deadlock
the database using these functions: something which is impossible
using the other access functions.
A return value of 0 indicates success and -1 indicates failure.