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 */
017package org.apache.camel;
018
019import java.util.concurrent.RejectedExecutionException;
020import java.util.concurrent.RejectedExecutionHandler;
021import java.util.concurrent.ThreadPoolExecutor;
022import javax.xml.bind.annotation.XmlEnum;
023import javax.xml.bind.annotation.XmlType;
024
025/**
026 * Represent the kinds of options for rejection handlers for thread pools.
027 * <p/>
028 * These options are used for fine grained thread pool settings, where you
029 * want to control which handler to use when a thread pool cannot execute
030 * a new task.
031 * <p/>
032 * Camel will by default use <tt>CallerRuns</tt>.
033 */
034@XmlType
035@XmlEnum
036public enum ThreadPoolRejectedPolicy {
037
038    Abort, CallerRuns, DiscardOldest, Discard;
039
040    public RejectedExecutionHandler asRejectedExecutionHandler() {
041        if (this == Abort) {
042            return new RejectedExecutionHandler() {
043                @Override
044                public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
045                    if (r instanceof Rejectable) {
046                        ((Rejectable)r).reject();
047                    } else {
048                        throw new RejectedExecutionException("Task " + r.toString() + " rejected from " + executor.toString());
049                    }
050                }
051
052                @Override
053                public String toString() {
054                    return "Abort";
055                }
056            };
057        } else if (this == CallerRuns) {
058            return new ThreadPoolExecutor.CallerRunsPolicy() {
059                @Override
060                public String toString() {
061                    return "CallerRuns";
062                }
063            };
064        } else if (this == DiscardOldest) {
065            return new RejectedExecutionHandler() {
066                @Override
067                public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
068                    if (!executor.isShutdown()) {
069                        Runnable rejected = executor.getQueue().poll();
070                        if (rejected instanceof Rejectable) {
071                            ((Rejectable) rejected).reject();
072                        }
073                        executor.execute(r);
074                    }
075                }
076
077                @Override
078                public String toString() {
079                    return "DiscardOldest";
080                }
081            };
082        } else if (this == Discard) {
083            return new RejectedExecutionHandler() {
084                @Override
085                public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
086                    if (r instanceof Rejectable) {
087                        ((Rejectable) r).reject();
088                    }
089                }
090
091                @Override
092                public String toString() {
093                    return "Discard";
094                }
095            };
096        }
097        throw new IllegalArgumentException("Unknown ThreadPoolRejectedPolicy: " + this);
098    }
099
100}