unlock with delete

[Mika Tapanainen]

Hello,

I have in my DB interface

    
public void delete(int recNo, long lockCookie) throws RecordNotFoundException, SecurityException;
public long lock(int recNo) throws RecordNotFoundException;
public void unlock(int recNo, long cookie) throws RecordNotFoundException, SecurityException;

There is a little bit difficult situation:

if I run

   
long lockCookie = lock(1);
delete(1, lockCookie);
unlock(1, lockCookie);

RecordNotFoundException should be thrown for the unlock, because record 1 is already deleted.

I handled this situation so that delete unlocks the record and notifies all waiters, but I have started to think if I should change the implementation.

What you think, should there be unlock after delete? I think I can do the new implementation, where the RecordNotFoundException is not thrown from the unlock method if the record is deleted and the lockCookie is correct.

BR,

Mika

[Roel De Nijs]

Hi Mika,

Of course a deleted record should be unlocked, otherwise you end up having a deadlock. For example with this scenario:

 client1.lock(1);
 client2.lock(1); // waiting for record 1
 client1.delete(1);

client2 will now wait forever...

In my solution there is just 1 method (besides read and find) that throws a RNFE and that's the lock-method. Because if the lock-method has successfully locked a record, another client can't do anything with that record (so it certainly can't be deleted). If some other client can update/delete that record, there is something wrong with the locking mechanism. So I created my own custom interface (extending the required one) and i copied the delete, update and unlock method signatures but without the throws RecordNotFoundException clause. I was very pleased with this smart "work-around".

Kind regards,
Roel

[Mika Tapanainen]

Thanks Roel,

I read yesterday some discussions and removed RNFE from the delete, update and unlock methods as you wrote here also.

Mika

[Roel De Nijs]

Hi Mika,

I hope you didn't delete it from Sun's interface, because as far as I know it's forbidden to make changes in that interface.

Kind regards,
Roel

[Mika Tapanainen]

Hi Roel,

Thanks for the reminder! I didn't change Sun's interface.

Mika