1 //
2 // ========================================================================
3 // Copyright (c) 1995-2016 Mort Bay Consulting Pty. Ltd.
4 // ------------------------------------------------------------------------
5 // All rights reserved. This program and the accompanying materials
6 // are made available under the terms of the Eclipse Public License v1.0
7 // and Apache License v2.0 which accompanies this distribution.
8 //
9 // The Eclipse Public License is available at
10 // http://www.eclipse.org/legal/epl-v10.html
11 //
12 // The Apache License v2.0 is available at
13 // http://www.opensource.org/licenses/apache2.0.php
14 //
15 // You may elect to redistribute this code under either of these licenses.
16 // ========================================================================
17 //
18
19 package org.eclipse.jetty.util;
20
21 /**
22 * <p>A callback abstraction that handles completed/failed events of asynchronous operations.</p>
23 *
24 * <p>Semantically this is equivalent to an optimise Promise<Void>, but callback is a more meaningful
25 * name than EmptyPromise</p>
26 */
27 public interface Callback
28 {
29 /**
30 * Instance of Adapter that can be used when the callback methods need an empty
31 * implementation without incurring in the cost of allocating a new Adapter object.
32 */
33 static Callback NOOP = new Callback(){};
34
35
36 /**
37 * <p>Callback invoked when the operation completes.</p>
38 *
39 * @see #failed(Throwable)
40 */
41 default void succeeded()
42 {}
43
44 /**
45 * <p>Callback invoked when the operation fails.</p>
46 * @param x the reason for the operation failure
47 */
48 default void failed(Throwable x)
49 {}
50
51 /**
52 * @return True if the callback is known to never block the caller
53 */
54 default boolean isNonBlocking()
55 {
56 return false;
57 }
58
59
60 /**
61 * Callback interface that declares itself as non-blocking
62 */
63 interface NonBlocking extends Callback
64 {
65 @Override
66 public default boolean isNonBlocking()
67 {
68 return true;
69 }
70 }
71
72
73 /**
74 * <p>Empty implementation of {@link Callback}</p>
75 */
76 @Deprecated
77 static class Adapter implements Callback
78 {}
79 }