sos.db
Interface TransactionPolicy

All Known Implementing Classes:

AbstractTransactionPolicy, DefaultReadWriteTransactionPolicy, DefaultTransactionPolicy

public interface TransactionPolicy

A policy that determines the behavior of database transactions. Specifically, a class that implements this interface is in charge of

• Locking database objects accessed during a transaction
• Detecting, avoiding, or eliminating transaction deadlocks
• Propagating an invocation on a database proxy object to the underlying database object

A requirement of a database is that its transactions must appear to be atomic and sequential. Typically, an implementation of this class will use a locking scheme to prevent two transactions from accessing the same object in a conflicting manner. In order to resolve deadlock, the implementation might use lock timeouts or a waits-for graph.

Since:

1.0

See Also:

AbstractTransactionPolicy, DefaultTransactionPolicy, DefaultReadWriteTransactionPolicy

Method Summary

java.lang.Object	invoke(TransactionSupport support, java.lang.reflect.Method method, java.lang.Object[] args) Invokes the specified method on the object referred to by support.
void	registerObject(TransactionSupport support, java.lang.Object object) Notifies this policy that there is a new database object.
void	startTransaction(TransactionSupport support) Notifies this policy that a top-level transaction is starting for the executing thread.
void	unregisterObjects(Database db, java.util.Set<java.lang.Object> oldKeys) Notifies this policy that objects have been removed from the database.

Method Detail

invoke

java.lang.Object invoke(TransactionSupport support,
                        java.lang.reflect.Method method,
                        java.lang.Object[] args)
                        throws java.lang.IllegalAccessException,
                               java.lang.reflect.InvocationTargetException,
                               java.io.IOException

Invokes the specified method on the object referred to by support. The database calls this method to invoke a method on a database object.

If the object can potentially be modified by the execution of method, the implementation should fetch the receiver using getObjectForWrite; otherwise, it should use getObjectForRead.

If the object needs to be locked during the execution of method, the implementation can use the object returned by getKey to identify the lock.

If this method throws a DatabaseException, the current transaction will be aborted and rolled back.

Parameters:

support - object to assist in transaction management

method - method to invoke on the object referred to by support

args - arguments to the method

Returns:

the result of the invocation of method

Throws:

java.lang.IllegalAccessException - if method is not accessible

java.lang.reflect.InvocationTargetException - if the invocation of method throws an exception. The exception returned by getCause is the method's exception.

java.io.IOException - if an I/O error occurs

See Also:

TransactionSupport.getKey(), TransactionSupport.getObjectForRead(), TransactionSupport.getObjectForWrite()

registerObject

void registerObject(TransactionSupport support,
                    java.lang.Object object)
                    throws java.io.IOException

Notifies this policy that there is a new database object. The database calls this method when an object is added to the database.

Parameters:

support - object to assist in transaction management

object - the object added to the database

Throws:

java.io.IOException - if an I/O error occurs

startTransaction

void startTransaction(TransactionSupport support)
                      throws java.io.IOException

Notifies this policy that a top-level transaction is starting for the executing thread. The database calls this method when a top-level transaction is starting.

Parameters:

support - object to assist in transaction management

Throws:

java.io.IOException - if an I/O error occurs

Since:

2.0

unregisterObjects

void unregisterObjects(Database db,
                       java.util.Set<java.lang.Object> oldKeys)

Notifies this policy that objects have been removed from the database. The database calls this method when objects are being removed from the database.

Parameters:

db - database for which the objects have been removed

oldKeys - set of objects that identify the objects being removed from the database