1 package org.eclipse.aether.util.concurrency;
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 static java.util.Objects.requireNonNull;
23
24 import java.util.concurrent.atomic.AtomicInteger;
25 import java.util.concurrent.atomic.AtomicReference;
26 import java.util.concurrent.locks.LockSupport;
27
28 /**
29 * A utility class to forward any uncaught {@link Error} or {@link RuntimeException} from a {@link Runnable} executed in
30 * a worker thread back to the parent thread. The simplified usage pattern looks like this:
31 *
32 * <pre>
33 * RunnableErrorForwarder errorForwarder = new RunnableErrorForwarder();
34 * for ( Runnable task : tasks )
35 * {
36 * executor.execute( errorForwarder.wrap( task ) );
37 * }
38 * errorForwarder.await();
39 * </pre>
40 */
41 public final class RunnableErrorForwarder
42 {
43
44 private final Thread thread = Thread.currentThread();
45
46 private final AtomicInteger counter = new AtomicInteger();
47
48 private final AtomicReference<Throwable> error = new AtomicReference<>();
49
50 /**
51 * Creates a new error forwarder for worker threads spawned by the current thread.
52 */
53 public RunnableErrorForwarder()
54 {
55 }
56
57 /**
58 * Wraps the specified runnable into an equivalent runnable that will allow forwarding of uncaught errors.
59 *
60 * @param runnable The runnable from which to forward errors, must not be {@code null}.
61 * @return The error-forwarding runnable to eventually execute, never {@code null}.
62 */
63 public Runnable wrap( final Runnable runnable )
64 {
65 requireNonNull( runnable, "runnable cannot be null" );
66
67 counter.incrementAndGet();
68
69 return new Runnable()
70 {
71 public void run()
72 {
73 try
74 {
75 runnable.run();
76 }
77 catch ( RuntimeException | Error e )
78 {
79 error.compareAndSet( null, e );
80 throw e;
81 }
82 finally
83 {
84 counter.decrementAndGet();
85 LockSupport.unpark( thread );
86 }
87 }
88 };
89 }
90
91 /**
92 * Causes the current thread to wait until all previously {@link #wrap(Runnable) wrapped} runnables have terminated
93 * and potentially re-throws an uncaught {@link RuntimeException} or {@link Error} from any of the runnables. In
94 * case multiple runnables encountered uncaught errors, one error is arbitrarily selected. <em>Note:</em> This
95 * method must be called from the same thread that created this error forwarder instance.
96 */
97 public void await()
98 {
99 awaitTerminationOfAllRunnables();
100
101 Throwable error = this.error.get();
102 if ( error != null )
103 {
104 if ( error instanceof RuntimeException )
105 {
106 throw (RuntimeException) error;
107 }
108 else if ( error instanceof ThreadDeath )
109 {
110 throw new IllegalStateException( error );
111 }
112 else if ( error instanceof Error )
113 {
114 throw (Error) error;
115 }
116 throw new IllegalStateException( error );
117 }
118 }
119
120 private void awaitTerminationOfAllRunnables()
121 {
122 if ( !thread.equals( Thread.currentThread() ) )
123 {
124 throw new IllegalStateException( "wrong caller thread, expected " + thread + " and not "
125 + Thread.currentThread() );
126 }
127
128 boolean interrupted = false;
129
130 while ( counter.get() > 0 )
131 {
132 LockSupport.park();
133
134 if ( Thread.interrupted() )
135 {
136 interrupted = true;
137 }
138 }
139
140 if ( interrupted )
141 {
142 Thread.currentThread().interrupt();
143 }
144 }
145
146 }