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;
022
023import javax.xml.bind.annotation.XmlEnum;
024import javax.xml.bind.annotation.XmlType;
025
026/**
027 * Represent the kinds of options for rejection handlers for thread pools.
028 * <p/>
029 * These options are used for fine grained thread pool settings, where you
030 * want to control which handler to use when a thread pool cannot execute
031 * a new task.
032 * <p/>
033 * Camel will by default use <tt>CallerRuns</tt>.
034 */
035@XmlType
036@XmlEnum
037public enum ThreadPoolRejectedPolicy {
038
039    Abort, CallerRuns, DiscardOldest, Discard;
040
041    public RejectedExecutionHandler asRejectedExecutionHandler() {
042        if (this == Abort) {
043            return new RejectedExecutionHandler() {
044                @Override
045                public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
046                    if (r instanceof Rejectable) {
047                        ((Rejectable)r).reject();
048                    } else {
049                        throw new RejectedExecutionException("Task " + r.toString() + " rejected from " + executor.toString());
050                    }
051                }
052
053                @Override
054                public String toString() {
055                    return "Abort";
056                }
057            };
058        } else if (this == CallerRuns) {
059            return new ThreadPoolExecutor.CallerRunsPolicy() {
060                @Override
061                public String toString() {
062                    return "CallerRuns";
063                }
064            };
065        } else if (this == DiscardOldest) {
066            return new RejectedExecutionHandler() {
067                @Override
068                public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
069                    if (!executor.isShutdown()) {
070                        Runnable rejected = executor.getQueue().poll();
071                        if (rejected instanceof Rejectable) {
072                            ((Rejectable) rejected).reject();
073                        }
074                        executor.execute(r);
075                    }
076                }
077
078                @Override
079                public String toString() {
080                    return "DiscardOldest";
081                }
082            };
083        } else if (this == Discard) {
084            return new RejectedExecutionHandler() {
085                @Override
086                public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
087                    if (r instanceof Rejectable) {
088                        ((Rejectable) r).reject();
089                    }
090                }
091
092                @Override
093                public String toString() {
094                    return "Discard";
095                }
096            };
097        }
098        throw new IllegalArgumentException("Unknown ThreadPoolRejectedPolicy: " + this);
099    }
100
101}