2.3.3. Locking policy

Unlike many other systems, locks in TxCore are not special system types. Instead they are simply instances of other TxCore objects (the class Lock which is also derived from StateManager so that locks may be made persistent if required and can also be named in a simple fashion). Furthermore, LockManager deliberately has no knowledge of the semantics of the actual policy by which lock requests are granted. Such information is maintained by the actual Lock class instances which provide operations (the conflictsWith operation) by which LockManager can determine if two locks conflict or not. This separation is important in that it allows the programmer to derive new lock types from the basic Lock class and by providing appropriate definitions of the conflict operations enhanced levels of concurrency may be possible.
public class LockMode
    public static final int READ;
    public static final int WRITE;

public class LockStatus
    public static final int LOCKFREE;
    public static final int LOCKHELD;
    public static final int LOCKRETAINED;

public class Lock extends StateManager
    public Lock (int lockMode);
    public boolean conflictsWith  (Lock otherLock);
    public boolean modifiesObject ();
    public boolean restore_state (InputObjectState os, int ObjectType);
    public boolean save_state (OutputObjectState os, int ObjectType);
    public String type ();
    . . .
The Lock class provides a modifiesObject operation which LockManager uses to determine if granting this locking request requires a call on modified. This operation is provided so that locking modes other than simple read and write can be supported. The supplied Lock class supports the traditional multiple reader/single writer policy.