1 /*******************************************************************************
2 * Copyright (c) 2007, 2010 Association for Decentralized Information Management
4 * All rights reserved. This program and the accompanying materials
5 * are made available under the terms of the Eclipse Public License v1.0
6 * which accompanies this distribution, and is available at
7 * http://www.eclipse.org/legal/epl-v10.html
10 * VTT Technical Research Centre of Finland - initial API and implementation
11 *******************************************************************************/
12 package org.simantics.db.request;
14 import org.simantics.db.AsyncReadGraph;
15 import org.simantics.db.Session;
16 import org.simantics.db.exception.CancelTransactionException;
17 import org.simantics.db.procedure.AsyncProcedure;
20 * TODO: fix this documentation, it is completely out-of-date!
22 * The <code>GraphRequest</code> interface is used to create transaction
23 * requests to Simantics database implementations. Both read and write
24 * transaction requests use the same interface.
27 * The actual work carried out by the implemented request should be done in the
28 * <code>perform</code> method. It receives a <code>Graph</code> instance as
29 * the only argument which is the interface for actually reading and writing the
33 * Transaction requests can be made to the database by creating your own
34 * <code>GraphRequest</code> instance and putting it in the request queue of
35 * the database session through the {@link Session} interface. The database
36 * session is responsible for executing the queued requests in a thread of its
37 * choice, or possibly/preferably multiple threads. The database session can
38 * allow multiple read-only requests to occur simultaneously, but read-write
39 * requests require exclusive database access. In other words only one
40 * read-write request can be in execution simultaneously.
43 * This interface also has two callbacks - <code>handleException</code> for
44 * allowing handling any exceptions thrown by <code>perform</code> and
45 * <code>requestCompleted</code> for performing actions after a request has
46 * been successfully completed.
48 * @author Antti Villberg
53 public interface AsyncRead<Result> {
56 * When a <code>GraphRequest</code> is serviced by the database session
57 * the method <code>perform</code> is invoked.
60 * Perform receives an object instance implementing the <code>Graph</code>
61 * interface which provides the only way to read/write the graph data model.
62 * The Graph instance must only be valid during the execution of the
63 * <code>perform</code> method and therefore should not be stored for use
64 * outside of its execution.
67 * The general contract of the method <code>perform</code> is that it may
68 * take any action whatsoever which involves reading or writing the data
69 * model through the received Graph instance.
71 * @param g an interface for reading and writing the data model
72 * @return the result status of the request which affects how the
73 * transaction proceeds, see GraphRequestStatus for more information
74 * @throws Exception when anything goes wrong inside the request thread
75 * @throws CancelTransactionException to indicate that the request needs to
76 * be cancelled and any changes rolled back
78 void perform(AsyncReadGraph graph, AsyncProcedure<Result> procedure);