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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 java.util.Random; |
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import uk.ac.ukc.iscream.util.*; |
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/** |
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*/ |
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public static final String REVISION = "$Revision$"; |
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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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//---STATIC METHODS--- |
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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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//---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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// get size before adding to the Queue |
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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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// 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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} |
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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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status += "queue"+i+"=\"[deleted]\" "; |
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} |
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} |
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status += "total=\""+_count+"\"></queue>"; |
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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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//---PRIVATE METHODS--- |
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/** |
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* This method removes an item from a Queue, using a method |
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* requested at construction. |
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* |
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* @param list The LinkedList from which to remove an item. |
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*/ |
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private void removeQueueItem(LinkedList list) { |
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// look at our algorithm |
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// remove a random item from the list |
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if(_removeAlgorithm==RANDOM) { |
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// new Random, with a good seed |
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Random rand = new Random(System.currentTimeMillis()); |
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int i = rand.nextInt(_maxSize); |
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synchronized(this) { |
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list.remove(i); |
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} |
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} |
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// remove the first item from the list |
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else if(_removeAlgorithm==FIRST) { |
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synchronized(this) { |
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list.removeFirst(); |
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} |
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} |
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// remove the last item from the list |
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else if(_removeAlgorithm==LAST) { |
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synchronized(this) { |
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list.removeLast(); |
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} |
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} |
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} |
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|
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//---ACCESSOR/MUTATOR METHODS--- |
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//---ATTRIBUTES--- |
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* A reference to our QueueMonitor, if we have one. |
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*/ |
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private QueueMonitor _queueMon = null; |
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|
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/** |
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* The maximum size of any Queue. |
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*/ |
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private int _maxSize = -1; |
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|
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/** |
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* The remove algorithm to use upon a Queue reaching |
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* it's maximum size. |
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*/ |
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private int _removeAlgorithm = -1; |
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|
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/** |
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* This is the friendly identifier of the |
