forced to lock and then read

[Bob Stone]

Hi Randchers,

I�ve finished my B&S coding, and now I am doing Data.class testing for updateRecord() and deleteRecord(), but found the lockRecord method is not thread�safe. Here are the codes:

    
    Public void lockRecord(long recNo) throws RecordNotFoundException {
        long lockCookie = -1
        
        if (data.readRecord(recNo) == null) {
            throw new RecordNotFoundException(...);
        } else {
            try {
                lockCookie = bookManager.lockRecord(recNo);
            } catch (InterrupedException) {
               ....
            }
        }
        return lockCookie;
    }
    

where data is an instance of Data.class and bookManager is to logically lock (place an entry in a WeakHashMap) a record which prior to deleting or updating.
When multiple threads, delete and update together, acquire same record, a delete thread can lock a record that has been deleted. Say:
a delete thread and a update thread both can find the same record, now the update thread go asleep and the delete record carries on and finally removes the record. Afterward, a update record wakes up and then successfully locks up an unexisting record.

To fix it, an alternative is to lock record first regardless of it's existence. Here is the method

   
   Public void lockRecord(long recNo) throws RecordNotFoundException {
        
        long lockCookie = bookManager.lockRecord(recNo);
        
        if (data.readRecord(recNo) == null) {
            throw new RecordNotFoundException(...);
        } else {
            try {
                bookManager.unlockRecord(recNo);
            } catch (SecurityException) {
               throws new RecordNotFoundException("Cookie held by another client....");
            }
        }
        return lockCookie;
    }

Is it odd to handle securityException exception by rethrow a RecordNotFoundException exception with "Cookie held by another..." ? Or other solutions can anyone draw my attention?

Thanks very much

[Bob Stone]

I made mistake, the alternative should be :

 Public void lockRecord(long recNo) throws RecordNotFoundException {
        
        long lockCookie = bookManager.lockRecord(recNo);
        
        if (data.readRecord(recNo) == null) {
            try {
                bookManager.unlockRecord(recNo);
            } catch (SecurityException) {
                throw new RecordNotFoundException("Cookie held by another client....");
            }
            throw new RecordNotFoundException(...);
        }
        return lockCookie;
    }