lock & read or just read?

[Alex Sharkoff]

Hi all,

My assignment has the following comment on the lock(int) method: Locks a record so that it can only be updated or deleted by this client.. So what I am thinking is to only use the physical locking (ie locking on the database file) when reading a record. An additional record locking (along with physical locking) will be only used when updating/deleting a record.

DBClient class

public Contractor read(int recNo) throws RecordNotFoundException {
DBMain db = new Data(DataType.CONTRACTOR);

// No record locking !!!

String[] rec = db.read(recNo);

// No record unlocking !!!

....
}

Data class:

public String[] read(int recNo) throws RecordNotFoundException {
String[] record = null;

checkIfRecordExists(recNo); 

// there is only one instance of dbFile in JVM , therefore we 
// need to get its monitor to ensure that only one thread at a time can 
// access it (when updating/creating records we're synchronizing on it as well)
synchronized(dbFile) {
// the record could have been deleted while waiting for the monitor
// check again
checkIfRecordExists(recNo); 

record = dbFile.read(recNo);
}

return record;
}
 

Do you think it is an appropriate approach to the read method?


[ December 08, 2005: Message edited by: Alex Sharkoff ]

[Andrew Monkhouse]

Hi Alex,

I think that is suitable for the read method.

Regards, Andrew

[Alex Sharkoff]

thanks a lot, Andrew.