2 * Copyright (c) 2014 Cisco Systems, Inc. and others. All rights reserved.
4 * This program and the accompanying materials are made available under the
5 * terms of the Eclipse Public License v1.0 which accompanies this distribution,
6 * and is available at http://www.eclipse.org/legal/epl-v10.html
8 package org.opendaylight.controller.md.sal.common.api.data;
10 import org.opendaylight.yangtools.concepts.Path;
12 import com.google.common.base.Optional;
13 import com.google.common.util.concurrent.ListenableFuture;
17 * Provides a stateful read view of the data tree.
20 * View of the data tree is a stable point-in-time snapshot of the current data tree state when
21 * the transaction was created. It's state and underlying data tree
22 * is not affected by other concurrently running transactions.
25 * <b>Implementation Note:</b> This interface is not intended to be implemented
26 * by users of MD-SAL, but only to be consumed by them.
28 * <h2>Transaction isolation example</h2>
29 * Lets assume initial state of data tree for <code>PATH</code> is <code>A</code>.
32 * txRead = broker.newReadOnlyTransaction(); // read Transaction is snapshot of data
33 * txWrite = broker.newReadWriteTransactoin(); // concurrent write transaction
35 * txRead.read(OPERATIONAL,PATH).get(); // will return Optional containing A
36 * txWrite = broker.put(OPERATIONAL,PATH,B); // writes B to PATH
38 * txRead.read(OPERATIONAL,PATH).get(); // still returns Optional containing A
40 * txWrite.commit().get(); // data tree is updated, PATH contains B
41 * txRead.read(OPERATIONAL,PATH).get(); // still returns Optional containing A
43 * txAfterCommit = broker.newReadOnlyTransaction(); // read Transaction is snapshot of new state
44 * txAfterCommit.read(OPERATIONAL,PATH).get(); // returns Optional containing B;
48 * <b>Note:</b> example contains blocking calls on future only to illustrate
49 * that action happened after other asynchronous action. Use of blocking call
50 * {@link ListenableFuture#get()} is discouraged for most uses and you should
52 * {@link com.google.common.util.concurrent.Futures#addCallback(ListenableFuture, com.google.common.util.concurrent.FutureCallback)}
53 * or other functions from {@link com.google.common.util.concurrent.Futures} to
54 * register more specific listeners.
57 * Type of path (subtree identifier), which represents location in
60 * Type of data (payload), which represents data payload
62 public interface AsyncReadTransaction<P extends Path<P>, D> extends AsyncTransaction<P, D> {
66 * Reads data from provided logical data store located at the provided path.
68 * If the target is a subtree, then the whole subtree is read (and will be
69 * accessible from the returned data object).
72 * Logical data store from which read should occur.
74 * Path which uniquely identifies subtree which client want to
76 * @return Listenable Future which contains read result
78 * <li>If data at supplied path exists the
79 * {@link ListeblaFuture#get()} returns Optional object containing
80 * data once read is done.
81 * <li>If data at supplied path does not exists the
82 * {@link ListenbleFuture#get()} returns {@link Optional#absent()}.
85 ListenableFuture<Optional<D>> read(LogicalDatastoreType store, P path);