DB Interface implementation

[anthony chan]

Dear all,

In the DB interface that provided by the instruction. The explaination of method "lock" said "Locks a record so that it can only be updated or deleted by this client." Does the record mean one record in the data file or it means the data file. Since I know how to lock the data file, but I don't have any idea to lock one record inside the data file.

Thanks
anthony chan

[Roel De Nijs]

Hi Anthony,

I guess you should just lock that record, not the complete data file. So your program should deal with following sequence without any problems:

client1.lock(1);
client2.lock(2);
client2.update(2, newData);
client1.update(1, newData);
client2.unlock(2);
client3.lock(3);
client3.update(3, newData);
client3.unlock(3);
client1.unlock(1);

So while client1 holds the lock on record1, client2 is able to update the record on which it owns the lock.

Kind regards,
Roel