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/* |
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* i-scream central monitoring system |
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* Copyright (C) 2000-2002 i-scream |
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* |
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* This program is free software; you can redistribute it and/or |
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* modify it under the terms of the GNU General Public License |
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* as published by the Free Software Foundation; either version 2 |
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* of the License, or (at your option) any later version. |
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* |
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* This program is distributed in the hope that it will be useful, |
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* but WITHOUT ANY WARRANTY; without even the implied warranty of |
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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* GNU General Public License for more details. |
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* |
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* You should have received a copy of the GNU General Public License |
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* along with this program; if not, write to the Free Software |
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. |
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*/ |
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|
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//---PACKAGE DECLARATION--- |
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package uk.ac.ukc.iscream.util; |
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package uk.org.iscream.cms.server.util; |
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|
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//---IMPORTS--- |
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import java.util.LinkedList; |
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import java.util.NoSuchElementException; |
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import uk.ac.ukc.iscream.util.*; |
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import java.util.Random; |
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import uk.org.iscream.cms.server.util.*; |
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|
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/** |
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* A Queue class designed to operate in a multi-threaded environment, with |
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*/ |
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public static final String REVISION = "$Revision$"; |
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|
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/** |
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* Pass to constructor to remove a RANDOM item from |
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* the Queue upon reaching the maximum limit. |
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*/ |
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public static final int RANDOM = 0; |
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|
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/** |
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* Pass to constructor to remove the FIRST item from |
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* the Queue upon reaching the maximum limit. |
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*/ |
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public static final int FIRST = 1; |
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|
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/** |
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* Pass to constructor to remove the LAST item from |
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* the Queue upon reaching the maximum limit. |
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*/ |
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public static final int LAST = 2; |
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|
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/** |
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* Pass to constructor to drop the new item upon reaching |
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* the maximum Queue limit. |
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*/ |
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public static final int DROP = 3; |
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|
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/** |
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* To allow opposite lookups. |
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*/ |
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public static final String[] algorithms = {"RANDOM", "FIRST", "LAST", "DROP"}; |
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|
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//---STATIC METHODS--- |
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|
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//---CONSTRUCTORS--- |
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|
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/** |
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* Constructs a new Queue with a maximum size limit on |
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* any individual queue. This should be used to stop |
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* conditions where the Queue cannot be guaranteed to |
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* be emptied as quick as it's filled. |
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* |
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* An algorithm will be used to remove data when new data |
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* arrives. There may be choices of algorithms later on. |
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* |
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* @param maxSize the upper limit for a queue |
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* @param removeAlgorithm the remove algorithm to use upon reaching the maxSize |
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*/ |
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public Queue(int maxSize, int removeAlgorithm) { |
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_maxSize = maxSize; |
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_removeAlgorithm = removeAlgorithm; |
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} |
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|
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/** |
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* Constructs a Queue with no maximum size. |
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*/ |
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public Queue() { |
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_maxSize = -1; |
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} |
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|
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//---PUBLIC METHODS--- |
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for(int i=0; i < _lists.size(); i++) { |
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// skip over any gaps left in the list |
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if(_lists.get(i) != null) { |
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int s = ((LinkedList) _lists.get(i)).size(); |
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synchronized(this) { |
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// add() does the same thing, but this ensures behaviour |
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((LinkedList) _lists.get(i)).addLast(o); |
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} |
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// if the queue was empty before the add it is possible |
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// that a consumer is waiting... so we notify them |
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if (s == 0) { |
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synchronized(((LinkedList) _lists.get(i))) { |
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((LinkedList) _lists.get(i)).notifyAll(); |
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synchronized(((LinkedList) _lists.get(i))) { |
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// get size before adding to the Queue |
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int s = ((LinkedList) _lists.get(i)).size(); |
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// check whether we need to remove an item from the current Queue |
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if(_maxSize!=-1 && s>=_maxSize && _removeAlgorithm!=DROP) { |
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// we need to remove an item |
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removeQueueItem((LinkedList) _lists.get(i)); |
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} |
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// check if we should add (not if Queue full, and using DROP algorithm) |
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if(!(s>=_maxSize && _removeAlgorithm==DROP)) { |
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// add the next item, ensuring we lock |
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synchronized(this) { |
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// LinkedList.add() does the same thing, but this ensures behaviour |
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((LinkedList) _lists.get(i)).addLast(o); |
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} |
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// if the queue was empty before the add it is possible |
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// that a consumer is waiting... so we notify them |
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//synchronized(((LinkedList) _lists.get(i))) { |
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((LinkedList) _lists.get(i)).notifyAll(); |
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//} |
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} |
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} |
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} |
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} |
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* This method returns an object from the front of a given queue. |
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* It will block until data exists in the queue if required. |
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* |
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* @param The queue to retrieve data from. |
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* @return The object from the front of the queue. |
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* @throws InvalidQueueException if the queue does not exist. |
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*/ |
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throw new InvalidQueueException("Requested queue "+queue+" does not exist"); |
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} |
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// block if the queue is empty |
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if (((LinkedList) _lists.get(queue)).size() == 0) { |
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synchronized(((LinkedList) _lists.get(queue))) { |
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synchronized(((LinkedList) _lists.get(queue))) { |
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if (((LinkedList) _lists.get(queue)).size() == 0) { |
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try { ((LinkedList) _lists.get(queue)).wait(); } catch(Exception e) {} |
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} |
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} |
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} |
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return o; |
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} |
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|
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/** |
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* This method returns a textual status of the queues. It |
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* is merely for observation, and would most likely be used |
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* by a larger "monitoring" component. Information returned |
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* includes the current size of each queue, and the total |
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* items passed through. |
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* This method releases a get() method that's currently |
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* waiting on an empty queue. This was designed for |
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* shutdown() type methods that may have problems closing |
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* if the thread of control is waiting on a queue. |
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* |
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* @return A String message containing status information. |
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* @param queue the queue to release. |
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*/ |
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public String status() { |
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String status = ""; |
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public void releaseQueue(int queue) { |
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synchronized(((LinkedList) _lists.get(queue))) { |
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((LinkedList) _lists.get(queue)).notifyAll(); |
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} |
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} |
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|
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/** |
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* This method erases the contents of a given queue. This |
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* method should be used with care. It can only empty one |
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* internal queue, not all of them. This must be called |
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* multiple times to empty all queues. |
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* |
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* @param queue the queue to empty. |
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*/ |
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public void clearQueue(int queue) { |
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synchronized(this) { |
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((LinkedList) _lists.get(queue)).clear(); |
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} |
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} |
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|
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/** |
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* This method returns an XML textual status of the queues. |
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* It is merely for observation, and would most likely be |
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* used by a larger "monitoring" component. Information |
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* returned includes the current size of each queue, and |
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* the total items passed through. |
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* |
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* @return A String message containing status information in XML format |
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*/ |
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public String xmlStatus() { |
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String status = "<queue "; |
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for(int i=0; i < _lists.size(); i++) { |
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// check for null entries |
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if(_lists.get(i) != null) { |
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status += "Queue number "+i+" contains "+((LinkedList) _lists.get(i)).size()+" elements"; |
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status += "\n"; |
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status += "queue"+i+"=\""+((LinkedList) _lists.get(i)).size()+"\" "; |
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} |
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else { |
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status += "Slot number "+i+" is currently empty"; |
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status += "\n"; |
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status += "queue"+i+"=\"[deleted]\" "; |
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} |
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} |
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status += "A total of "+_count+" elements have been added to the queues"; |
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status += "total=\""+_count+"\""; |
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if(_maxSize != -1) { |
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status += " maxSize=\""+_maxSize+"\""; |
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} |
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status += "></queue>"; |
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return status; |
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} |
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|
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/** |
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* Returns the size of a given queue. A consumer can use |
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* this to see how big their queue is at any given time. |
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* they should use their queue number as the parameter. |
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* |
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* @param queue The queue number to query. |
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* @return the current size of the queue. |
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* @throws InvalidQueueException if the queue does not exist. |
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*/ |
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public int queueSize(int queue) throws InvalidQueueException { |
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if (queue >= _lists.size() || _lists.get(queue) == null) { |
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throw new InvalidQueueException("Requested queue "+queue+" does not exist"); |
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} |
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return ((LinkedList) _lists.get(queue)).size(); |
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} |
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|
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/** |
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* Returns the total numer of elements to have passed |
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* through this queue. This is essentially a counter |
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* on the add method. |
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* |
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* @return the element-ometer. |
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*/ |
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public int elementCount() { |
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return _count; |
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} |
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|
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/** |
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* This method assigns a queue to a consumer. The idea behind |
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* this is to ensure that only 1 consumer can be associated with |
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* a given queue, otherwise the whole "blocking" thing fails |
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* |
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* @return An integer to be passed to the get() method. |
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*/ |
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public int getQueue() { |
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public synchronized int getQueue() { |
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int pos = -1; |
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for(int i=0; i < _lists.size(); i++) { |
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if(_lists.get(i) == null) { |
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* |
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* @param queue The integer identifier for the queue, given by getQueue(). |
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*/ |
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public void removeQueue(int queue) { |
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public synchronized void removeQueue(int queue) { |
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_lists.set(queue, null); |
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} |
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|
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/** |
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* Start a monitor on our own Queue. This will log XML |
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* statistics about our Queue to a given Queue (could be |
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* the one being monitored). |
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* |
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* @param interval The long interval, in milliseconds, at which to take samples |
304 |
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* @param destQueue The queue to monitor to |
305 |
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* @param name A name to identify this Queue with |
306 |
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* @return whether we succeeded |
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*/ |
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public boolean startMonitor(long interval, Queue destQueue, String name) { |
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if(_queueMon == null) { |
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// start a monitor |
311 |
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_queueMon = new QueueMonitor(this, destQueue, interval, name); |
312 |
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_queueMon.start(); |
313 |
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return true; |
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} |
315 |
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else { |
316 |
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// already have a monitor running |
317 |
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return false; |
318 |
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} |
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} |
320 |
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|
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/** |
322 |
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* Start a monitor on our own Queue. This will log XML |
323 |
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* statistics about our Queue to this Queue. |
324 |
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* |
325 |
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* @param interval The long interval, in milliseconds, at which to take samples |
326 |
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* @param name A name to identify this Queue with |
327 |
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* @return whether we succeeded |
328 |
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*/ |
329 |
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public boolean startMonitor(long interval, String name) { |
330 |
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return startMonitor(interval, this, name); |
331 |
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} |
332 |
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|
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/** |
334 |
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* Stop a monitor on our Queue if we have on running. |
335 |
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* |
336 |
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* @return whether we succeeded |
337 |
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*/ |
338 |
+ |
public boolean stopMonitor() { |
339 |
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if(_queueMon != null) { |
340 |
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// stop a monitor |
341 |
+ |
_queueMon.shutdown(); |
342 |
+ |
_queueMon = null; |
343 |
+ |
return true; |
344 |
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} |
345 |
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else { |
346 |
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// no monitor running |
347 |
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return false; |
348 |
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} |
349 |
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} |
350 |
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|
351 |
+ |
/** |
352 |
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* Overrides the {@link java.lang.Object#toString() Object.toString()} |
353 |
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* method to provide clean logging (every class should have this). |
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* |
355 |
< |
* This uses the uk.ac.ukc.iscream.util.FormatName class |
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* This uses the uk.org.iscream.cms.server.util.FormatName class |
356 |
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* to format the toString() |
357 |
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* |
358 |
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* @return the name of this class and its CVS revision |
358 |
> |
* @return the name of this class and its CVS revision. |
359 |
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*/ |
360 |
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public String toString() { |
361 |
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return FormatName.getName( |
365 |
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} |
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|
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//---PRIVATE METHODS--- |
368 |
< |
|
368 |
> |
|
369 |
> |
/** |
370 |
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* This method removes an item from a Queue, using a method |
371 |
> |
* requested at construction. |
372 |
> |
* |
373 |
> |
* @param list The LinkedList from which to remove an item. |
374 |
> |
*/ |
375 |
> |
private void removeQueueItem(LinkedList list) { |
376 |
> |
// look at our algorithm |
377 |
> |
// remove a random item from the list |
378 |
> |
if(_removeAlgorithm==RANDOM) { |
379 |
> |
// new Random, with a good seed |
380 |
> |
Random rand = new Random(System.currentTimeMillis()); |
381 |
> |
int i = rand.nextInt(_maxSize); |
382 |
> |
synchronized(this) { |
383 |
> |
list.remove(i); |
384 |
> |
} |
385 |
> |
} |
386 |
> |
// remove the first item from the list |
387 |
> |
else if(_removeAlgorithm==FIRST) { |
388 |
> |
synchronized(this) { |
389 |
> |
list.removeFirst(); |
390 |
> |
} |
391 |
> |
} |
392 |
> |
// remove the last item from the list |
393 |
> |
else if(_removeAlgorithm==LAST) { |
394 |
> |
synchronized(this) { |
395 |
> |
list.removeLast(); |
396 |
> |
} |
397 |
> |
} |
398 |
> |
} |
399 |
> |
|
400 |
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//---ACCESSOR/MUTATOR METHODS--- |
401 |
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|
402 |
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//---ATTRIBUTES--- |
411 |
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* passed through, for statistical purposes. |
412 |
|
*/ |
413 |
|
private int _count = 0; |
414 |
+ |
|
415 |
+ |
/** |
416 |
+ |
* A reference to our QueueMonitor, if we have one. |
417 |
+ |
*/ |
418 |
+ |
private QueueMonitor _queueMon = null; |
419 |
+ |
|
420 |
+ |
/** |
421 |
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* The maximum size of any Queue. |
422 |
+ |
*/ |
423 |
+ |
private int _maxSize = -1; |
424 |
+ |
|
425 |
+ |
/** |
426 |
+ |
* The remove algorithm to use upon a Queue reaching |
427 |
+ |
* it's maximum size. |
428 |
+ |
*/ |
429 |
+ |
private int _removeAlgorithm = -1; |
430 |
|
|
431 |
|
/** |
432 |
|
* This is the friendly identifier of the |