1 /* 2 * Copyright (c) 2000, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 package sun.jvm.hotspot.utilities; 26 27 /** The backend for the message queue abstraction. This class is 28 instantiated first and queried to provide the two "sides" of the 29 message queue. */ 30 31 import java.util.LinkedList; 32 33 public class MessageQueueBackend { 34 // The two queues 35 private MessageQueueImpl leftRightQueue; 36 private MessageQueueImpl rightLeftQueue; 37 MessageQueueBackend()38 public MessageQueueBackend() { 39 LinkedList leftRightPipe = new LinkedList(); 40 LinkedList rightLeftPipe = new LinkedList(); 41 leftRightQueue = new MessageQueueImpl(rightLeftPipe, leftRightPipe); 42 rightLeftQueue = new MessageQueueImpl(leftRightPipe, rightLeftPipe); 43 } 44 45 /** Get one of the two symmetric sides of this message queue. */ getFirstQueue()46 public MessageQueue getFirstQueue() { 47 return leftRightQueue; 48 } 49 50 /** Get second of the two symmetric sides of this message queue. */ getSecondQueue()51 public MessageQueue getSecondQueue() { 52 return rightLeftQueue; 53 } 54 55 private class MessageQueueImpl implements MessageQueue { 56 private LinkedList readList; 57 private LinkedList writeList; 58 MessageQueueImpl(LinkedList listToReadFrom, LinkedList listToWriteTo)59 public MessageQueueImpl(LinkedList listToReadFrom, LinkedList listToWriteTo) { 60 readList = listToReadFrom; 61 writeList = listToWriteTo; 62 } 63 readMessage()64 public Object readMessage() { 65 synchronized(readList) { 66 while (readList.isEmpty()) { 67 try { 68 readList.wait(); 69 } 70 catch (InterruptedException e) { 71 } 72 } 73 return readList.removeFirst(); 74 } 75 } 76 readMessageWithTimeout(long millis)77 public Object readMessageWithTimeout(long millis) { 78 synchronized(readList) { 79 if (readList.isEmpty()) { 80 if (millis == 0) { 81 return null; 82 } 83 try { 84 readList.wait(millis); 85 } 86 catch (InterruptedException e) { 87 } 88 } 89 // If list is still empty after wait, return null 90 if (readList.isEmpty()) { 91 return null; 92 } 93 return readList.removeFirst(); 94 } 95 } 96 writeMessage(Object obj)97 public void writeMessage(Object obj) { 98 synchronized(writeList) { 99 writeList.addLast(obj); 100 writeList.notify(); 101 } 102 } 103 } 104 } 105