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 Callback NOOP = new Callback()
34 {
35 };
36
37 /**
38 * <p>Callback invoked when the operation completes.</p>
39 *
40 * @see #failed(Throwable)
41 */
42 default void succeeded()
43 {
44 }
45
46 /**
47 * <p>Callback invoked when the operation fails.</p>
48 * @param x the reason for the operation failure
49 */
50 default void failed(Throwable x)
51 {
52 }
53
54 /**
55 * @return True if the callback is known to never block the caller
56 */
57 default boolean isNonBlocking()
58 {
59 return false;
60 }
61
62 /**
63 * Callback interface that declares itself as non-blocking
64 */
65 interface NonBlocking extends Callback
66 {
67 @Override
68 default boolean isNonBlocking()
69 {
70 return true;
71 }
72 }
73
74 class Nested implements Callback
75 {
76 private final Callback callback;
77
78 public Nested(Callback callback)
79 {
80 this.callback = callback;
81 }
82
83 public Nested(Nested nested)
84 {
85 this.callback = nested.callback;
86 }
87
88 @Override
89 public void succeeded()
90 {
91 callback.succeeded();
92 }
93
94 @Override
95 public void failed(Throwable x)
96 {
97 callback.failed(x);
98 }
99
100 @Override
101 public boolean isNonBlocking()
102 {
103 return callback.isNonBlocking();
104 }
105 }
106
107 /**
108 * <p>Empty implementation of {@link Callback}</p>
109 */
110 @Deprecated
111 class Adapter implements Callback
112 {
113 }
114 }