001    /**
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements.  See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache License, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License.  You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the License for the specific language governing permissions and
015     * limitations under the License.
016     */
017    package org.apache.camel;
018    
019    import java.util.concurrent.RejectedExecutionHandler;
020    import java.util.concurrent.ThreadPoolExecutor;
021    import javax.xml.bind.annotation.XmlEnum;
022    import javax.xml.bind.annotation.XmlType;
023    
024    /**
025     * Represent the kinds of options for rejection handlers for thread pools.
026     * <p/>
027     * These options are used for fine grained thread pool settings, where you
028     * want to control which handler to use when a thread pool cannot execute
029     * a new task.
030     * <p/>
031     * Camel will by default use <tt>CallerRuns</tt>.
032     */
033    @XmlType
034    @XmlEnum(String.class)
035    public enum ThreadPoolRejectedPolicy {
036    
037        Abort, CallerRuns, DiscardOldest, Discard;
038    
039        public RejectedExecutionHandler asRejectedExecutionHandler() {
040            if (this == Abort) {
041                return new RejectedExecutionHandler() {
042                    @Override
043                    public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
044                        if (r instanceof Rejectable) {
045                            ((Rejectable) r).reject();
046                        }
047                    }
048    
049                    @Override
050                    public String toString() {
051                        return "Abort";
052                    }
053                };
054            } else if (this == CallerRuns) {
055                return new ThreadPoolExecutor.CallerRunsPolicy() {
056                    @Override
057                    public String toString() {
058                        return "CallerRuns";
059                    }
060                };
061            } else if (this == DiscardOldest) {
062                return new RejectedExecutionHandler() {
063                    @Override
064                    public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
065                        if (!executor.isShutdown()) {
066                            Runnable rejected = executor.getQueue().poll();
067                            if (rejected instanceof Rejectable) {
068                                ((Rejectable) rejected).reject();
069                            }
070                            executor.execute(r);
071                        }
072                    }
073    
074                    @Override
075                    public String toString() {
076                        return "DiscardOldest";
077                    }
078                };
079            } else if (this == Discard) {
080                return new RejectedExecutionHandler() {
081                    @Override
082                    public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
083                        if (r instanceof Rejectable) {
084                            ((Rejectable) r).reject();
085                        }
086                    }
087    
088                    @Override
089                    public String toString() {
090                        return "Discard";
091                    }
092                };
093            }
094            throw new IllegalArgumentException("Unknown ThreadPoolRejectedPolicy: " + this);
095        }
096    
097    }