001/* 002 * Copyright (c) 2007-2017 Xplenty, Inc. All Rights Reserved. 003 * 004 * Project and contact information: http://www.cascading.org/ 005 * 006 * This file is part of the Cascading project. 007 * 008 * Licensed under the Apache License, Version 2.0 (the "License"); 009 * you may not use this file except in compliance with the License. 010 * You may obtain a copy of the License at 011 * 012 * http://www.apache.org/licenses/LICENSE-2.0 013 * 014 * Unless required by applicable law or agreed to in writing, software 015 * distributed under the License is distributed on an "AS IS" BASIS, 016 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 017 * See the License for the specific language governing permissions and 018 * limitations under the License. 019 */ 020 021package cascading.util; 022 023import java.util.Comparator; 024import java.util.Queue; 025import java.util.concurrent.PriorityBlockingQueue; 026 027import org.slf4j.Logger; 028import org.slf4j.LoggerFactory; 029 030/** 031 * ShutdownUtil is a private helper class for registering dependent shutdown hooks to maintain internal state 032 * information reliably when a jvm is shutting down. 033 * <p/> 034 * This api is not intended for public use. 035 */ 036public class ShutdownUtil 037 { 038 /** 039 * System property set to true when we have entered shutdown 040 */ 041 public static final String SHUTDOWN_EXECUTING = "cascading.jvm.shutdown.executing"; 042 public static final String SHUTDOWN_FORCE_NON_DAEMON = "cascading.jvm.shutdown.non-daemon"; 043 044 private static final Logger LOG = LoggerFactory.getLogger( ShutdownUtil.class ); 045 046 public static abstract class Hook 047 { 048 public enum Priority 049 { 050 FIRST, WORK_PARENT, WORK_CHILD, SERVICE_CONSUMER, SERVICE_PROVIDER, LAST 051 } 052 053 public abstract Priority priority(); 054 055 public abstract void execute(); 056 } 057 058 private static Queue<Hook> queue = new PriorityBlockingQueue<>( 20, new Comparator<Hook>() 059 { 060 @Override 061 public int compare( Hook lhs, Hook rhs ) 062 { 063 if( lhs == rhs ) 064 return 0; 065 066 if( lhs == null ) 067 return -1; 068 else if( rhs == null ) 069 return 1; 070 071 return lhs.priority().compareTo( rhs.priority() ); 072 } 073 } 074 ); 075 076 private static Thread shutdownHook; 077 078 public static void addHook( Hook hook ) 079 { 080 if( hook == null ) 081 throw new IllegalArgumentException( "hook may not be null" ); 082 083 registerShutdownHook(); 084 085 queue.add( hook ); 086 } 087 088 public static boolean removeHook( Hook hook ) 089 { 090 return queue.remove( hook ); 091 } 092 093 public static synchronized void registerShutdownHook() 094 { 095 if( shutdownHook != null ) 096 return; 097 098 final boolean isForceNonDaemon = Boolean.getBoolean( SHUTDOWN_FORCE_NON_DAEMON ); 099 100 shutdownHook = new Thread( "cascading shutdown hooks" ) 101 { 102 103 { 104 if( isForceNonDaemon ) 105 this.setDaemon( false ); 106 } 107 108 @Override 109 public void run() 110 { 111 System.setProperty( SHUTDOWN_EXECUTING, "true" ); 112 113 try 114 { 115 // These are not threads, so each one will be run in priority order 116 // blocking until the previous is complete 117 while( !queue.isEmpty() ) 118 { 119 Hook hook = null; 120 121 try 122 { 123 hook = queue.poll(); 124 125 // may get removed while shutdown is executing 126 if( hook == null ) 127 continue; 128 129 hook.execute(); 130 } 131 catch( Exception exception ) 132 { 133 LOG.error( "failed executing hook: {}, with exception: {}", hook, exception.getMessage() ); 134 LOG.debug( "with exception trace", exception ); 135 } 136 } 137 } 138 finally 139 { 140 System.setProperty( SHUTDOWN_EXECUTING, "false" ); 141 } 142 } 143 }; 144 145 Runtime.getRuntime().addShutdownHook( shutdownHook ); 146 } 147 148 public static void deregisterShutdownHook() 149 { 150 Runtime.getRuntime().removeShutdownHook( shutdownHook ); 151 } 152 }