1 package org.eclipse.aether.named.support;
2
3 /*
4 * Licensed to the Apache Software Foundation (ASF) under one
5 * or more contributor license agreements. See the NOTICE file
6 * distributed with this work for additional information
7 * regarding copyright ownership. The ASF licenses this file
8 * to you under the Apache License, Version 2.0 (the
9 * "License"); you may not use this file except in compliance
10 * with the License. You may obtain a copy of the License at
11 *
12 * http://www.apache.org/licenses/LICENSE-2.0
13 *
14 * Unless required by applicable law or agreed to in writing,
15 * software distributed under the License is distributed on an
16 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
17 * KIND, either express or implied. See the License for the
18 * specific language governing permissions and limitations
19 * under the License.
20 */
21
22 import java.util.concurrent.Callable;
23 import java.util.concurrent.TimeUnit;
24 import java.util.function.Predicate;
25
26 import org.slf4j.Logger;
27 import org.slf4j.LoggerFactory;
28
29 /**
30 * Retry helper: retries given {@code Callable} as long as it returns {@code null} (interpreted
31 * as "no answer yet") or given time passes. This helper implements similar semantics regarding
32 * caller threads as {@link java.util.concurrent.locks.Lock#tryLock(long, TimeUnit)} method does:
33 * blocks the caller thread until operation return non-{@code null} value within the given waiting
34 * time and the current thread has not been {@linkplain Thread#interrupt interrupted}.
35 *
36 * @since 1.7.3
37 */
38 public final class Retry
39 {
40 private static final Logger LOGGER = LoggerFactory.getLogger( Retry.class );
41
42 private Retry()
43 {
44 // no instances
45 }
46
47 /**
48 * Retries for given amount of time (time, unit) the passed in operation, sleeping given
49 * {@code sleepMills} between retries. In case operation returns {@code null}, it is assumed
50 * "is not done yet" state, so retry will happen (if time barrier allows). If time barrier
51 * passes, and still {@code null} ("is not done yet") is returned from operation, the
52 * {@code defaultResult} is returned.
53 */
54 public static <R> R retry( final long time,
55 final TimeUnit unit,
56 final long sleepMillis,
57 final Callable<R> operation,
58 final Predicate<Exception> retryPredicate,
59 final R defaultResult ) throws InterruptedException
60 {
61 long now = System.nanoTime();
62 final long barrier = now + unit.toNanos( time );
63 int attempt = 1;
64 R result = null;
65 while ( now < barrier && result == null )
66 {
67 try
68 {
69 result = operation.call();
70 if ( result == null )
71 {
72 LOGGER.trace( "Retry attempt {}: no result", attempt );
73 Thread.sleep( sleepMillis );
74 }
75 }
76 catch ( InterruptedException e )
77 {
78 throw e;
79 }
80 catch ( Exception e )
81 {
82 LOGGER.trace( "Retry attempt {}: operation failure", attempt, e );
83 if ( retryPredicate != null && !retryPredicate.test( e ) )
84 {
85 throw new IllegalStateException( e );
86 }
87 }
88 now = System.nanoTime();
89 attempt++;
90 }
91 return result == null ? defaultResult : result;
92 }
93
94 /**
95 * Retries attempting max given times the passed in operation, sleeping given
96 * {@code sleepMills} between retries. In case operation returns {@code null}, it is assumed
97 * "is not done yet" state, so retry will happen (if attempt count allows). If all attempts
98 * used, and still {@code null} ("is not done yet") is returned from operation, the
99 * {@code defaultResult} is returned.
100 * <p>
101 * Just to clear things up: 5 attempts is really 4 retries (once do it and retry 4 times). 0 attempts means
102 * "do not even try it", and this method returns without doing anything.
103 */
104 public static <R> R retry( final int attempts,
105 final long sleepMillis,
106 final Callable<R> operation,
107 final Predicate<Exception> retryPredicate,
108 final R defaultResult ) throws InterruptedException
109 {
110 int attempt = 1;
111 R result = null;
112 while ( attempt <= attempts && result == null )
113 {
114 try
115 {
116 result = operation.call();
117 if ( result == null )
118 {
119 LOGGER.trace( "Retry attempt {}: no result", attempt );
120 Thread.sleep( sleepMillis );
121 }
122 }
123 catch ( InterruptedException e )
124 {
125 throw e;
126 }
127 catch ( Exception e )
128 {
129 LOGGER.trace( "Retry attempt {}: operation failure", attempt, e );
130 if ( retryPredicate != null && !retryPredicate.test( e ) )
131 {
132 throw new IllegalStateException( e );
133 }
134 }
135 attempt++;
136 }
137 return result == null ? defaultResult : result;
138 }
139 }