10.3. Lock Management and Concurrency Control

Concurrency control information within JBoss Transaction Service is maintained by locks. Some of these locks need to be used by multiple objects in different processes. They can be held in a lock store, similar to the object store used for state information. The lock store used with JBoss Transaction Service has a restricted interface which allows flexibility with regard to implementation. Lock stores can be implemented in shared memory, on the Unix file system in several different formats, or as a remotely accessible store.

Note

As with all JBoss Transaction Service classes, the default lock stores are pure Java implementations. If you want to use more complex lock implementations, you must use native methods.

Example 10.8. Example LockStore Class

public class LockStore
{
    public abstract InputObjectState read_state (Uid u, String tName)
	throws LockStoreException;
    
    public abstract boolean remove_state (Uid u, String tname);
    public abstract boolean write_committed (Uid u, String tName,
					     OutputObjectState state);
};

10.3.1. Selecting a Lock Store Implementation

JBoss Transaction Service supports several different object store implementations. If the object model being used is Single, no lock store is required for maintaining locks, because the information about the object is not exported from it. However, if you use the Multiple model, different run-time environments may need to share concurrency control information. You can specify the implementation type of the lock store to use for all objects within a given execution environment using the com.arjuna.ats.txoj.lockstore.lockStoreType property. This variable can be either:
BasicLockStore
This is an in-memory implementation which does not include support for sharing of stored information between execution environments. You can extend it to include this functionality, if needed.
BasicPersistentLockStore
This is the default implementation. It stores locking information within the local file system. Execution environments that share the same file store can share concurrency control information. The root of the file system into which locking information is written is the LockStore/ directory within the JBoss Transaction Service installation directory. To override this location, set the com.arjuna.ats.txoj.lockstore.lockStoreDir property accordingly, or include the location in the CLASSPATH:

How to Override the lockStoreDir Property

  • java -D com.arjuna.ats.txoj.lockstore.lockStoreDir=/var/tmp/LockStore myprogram
  • java –classpath $CLASSPATH;/var/tmp/LockStore myprogram