Passed 360/400

[Mat Banik]

Hi to all,

I got my results today:

General Considerations (maximum = 100): 95
Documentation (maximum = 70): 70
O-O Design (maximum = 30): 29
GUI (maximum = 40): 28
Locking (maximum = 80): 58
Data store (maximum = 40): 40
Network server (maximum = 40): 40

360 - 90%

Did anybody get 58 on locking?? I did quick search and I didn�t find any post containing 58 on locking. It is just very odd to me. I�m thinking that I got it because of the �overcomplicated� orphaned deadlock prevention.

If someone is interested in details of my project go ahead and ask.

[Jeff Bosch]

Congratulations on passing. Yes, that seems to be a unique score for locking!

[Ken Boyd]

Did you provide all locking in Data.java (class name might be different in your assignment but must implement DB interface) and provide wrapper class for client to access methods of Data.java

Thanks

[Ken Boyd]

Congratulations!!

[Olena Golub]

Hello Matej,

Congratulations!! It's a very good score!!

What did you mean with

"overcomplicated" orphaned deadlock prevention.

? What was your strategy on deadlock prevention?
Thanks a lot for your answer!
Olena

[Mat Banik]

I used LockManager Singleton in my project.
Here follows the pseudo code:

  
private ReentrantLock recordsLock;
private Condition recordsCondition;
private Map<Integer, Long> lockMap;
 
    LockManager() {
        recordsLock = new ReentrantLock();
        recordsCondition = recordsLock.newCondition();
        lockMap = new HashMap<Integer, Long>(30);
    }
 
    long lockRecord(int recNo) throws RecordNotFoundException {
        recordsLock.lock();
        try {
            while (lockMap.containsKey(recNo)) {
   
                    recordsCondition.await();
            }
            retVal = getNextCookie();
 
            //store recNo and generated cookie in lockMap
 
        } finally {
            recordsLock.unlock();
        }
        return retVal; // cookie
    }

In the data class I have implemented above methods in Data's lock and unlock methods and also have design a way where the Data remembers last locked record and cookie.

Meaning if the client who is operating on the Data instance will loose connection the remote garbage collector will call
-RemoteDataImplementation.unreferenced()
this in turn calls
-Data. unlockOrphanedClient()
Where the Data instance has variable containing last accessed recNo and cookie and passes them to
-LockMangaer.unlock()

Hopefully this will give you and idea of what I have done.

[Andrew: Removed the unlock method - refer to "What is the policy on posting questions I saw on the exam / details of how to do the assignment?" in the JavaRanch SCJD FAQ for an explanation why.]
[ June 01, 2005: Message edited by: Andrew Monkhouse ]

[Darya Akbari]

Congratulations

You only need to change your signature

Regards,
Darya

[Mat Banik]

Thanks for notice, Darya. Good luck with your progress.

[Darya Akbari]

Thanks Matej,

I hope to change my signature also in near future

Regards,
Darya

[Andrew Monkhouse]

Congratulations Matej

[Mat Banik]

I want to thank you all for your congratulations.

Also I want to point out that the archives and javarach.com community helped me to boost-start my assignment. I found here many answers just by simple search.

When I was finished, I visited softlearn-systems.com and purchased softSCJD. It helped me greatly with my documentation.
Indrajeet and his team members helped me with their quality assurance, reviews and testing.
I avoided some serious assignment failures through their help. If you don�t have person to review your GUI and give you feedback these people are the ones you should turn to.

[Mat Banik]

Hi Andrew,

I'm sorry for the unlock method. I thought it was enough pseudo coded

[Andrew Monkhouse]

Hi Matej,

I'm sorry for the unlock method. I thought it was enough pseudo coded

Since the code was pretty much compilable as posted, I didn't take it as psuedo code, which is why I removed the unlock method.

I noticed that the lock method you presented does not throw the RecordNotFoundException (although the unlock method called another method that might have thrown this exception). I don't know if this was deliberatly removed from your posted code, or if you did leave it out of your submission - if so, it might account for some loss of marks.

Regards, Andrew

[Mat Banik]

Hi Andrew,

I noticed that the lock method you presented does not throw the RecordNotFoundException (although the unlock method called another method that might have thrown this exception)

It was intentional. It was intentional. I was counting on people to ask your question.

Anyway thanks for explanation of your reasons for removing the unlock method.

[Reza Rahman]

Matej:

Did you employ a deadlock detection technique? That does not appear to the case from the posted code? Could that be a potential suspect for the loss of the (minor) points?

In any case, congratulations on the great result!

Reza

[Mat Banik]

Did you employ a deadlock detection technique?

I started to implement the deadlock detection but I figured that I would have to do deep nesting if multiple client situations would occur. So I just mentioned in my choices and removed the deadlock prevention and restricted clients only to one lock at the time. If client has already one lock and requests another OneLockPerClientException is thrown.

It might be that they reduced my points because of that but the chances that the deadlock would occur are almost the same. At least that is what I�m thinking.

[DANNY JI]

i also get 58 on locking.

[Mat Banik]

i also get 58 on locking.

And why do you thing you got it?
Thanks for interest.

[John Smith]

  
private ReentrantLock recordsLock;
private Condition recordsCondition;
private Map<Integer, Long> lockMap;
 
    LockManager() {
        recordsLock = new ReentrantLock();
        recordsCondition = recordsLock.newCondition();
        lockMap = new HashMap<Integer, Long>(30);
    }
 
    long lockRecord(int recNo) throws RecordNotFoundException {
        recordsLock.lock();
        try {
            while (lockMap.containsKey(recNo)) {
   
                    recordsCondition.await();
            }
            retVal = getNextCookie();
 
            //store recNo and generated cookie in lockMap
 
        } finally {
            recordsLock.unlock();
        }
        return retVal; // cookie
    }

[/qb]<hr></blockquote>

Can you explain your reasons for having recordsLock and recordsCondition objects. I mean, why not simply this?

    synchronized long lockRecord(int recNo) {
        while (lockMap.containsKey(recNo))
        wait();
 //store recNo and generated cookie in lockMap
        return cookie;
    }

[ June 08, 2005: Message edited by: John Smith ]

[Mat Banik]

Reason is simple. I just wanted to exercise the tiger (1.5) locking functionality.

[Vishwa Kumba]

Congrats!

[Andrew Monkhouse]

Originally posted by Matej Banik:
Reason is simple. I just wanted to exercise the tiger (1.5) locking functionality.

[Mat Banik]

Congrats!

Kind thank you for your congrats. I would like to point out the beauty and newness of your expression, too all who like the English language as I do.

[Andrew Monkhouse]

I have moved this topic to the Sun Certification Results forum. You can now find it here.

Regards, Andrew
[ June 08, 2005: Message edited by: Andrew Monkhouse ]