--- projects/cms/source/util/uk/org/iscream/cms/util/Queue.java	2001/01/30 02:12:23	1.8
+++ projects/cms/source/util/uk/org/iscream/cms/util/Queue.java	2001/03/01 01:05:49	1.14
@@ -4,6 +4,7 @@ package uk.ac.ukc.iscream.util;
 //---IMPORTS---
 import java.util.LinkedList;
 import java.util.NoSuchElementException;
+import java.util.Random;
 import uk.ac.ukc.iscream.util.*;
 
 /**
@@ -13,7 +14,7 @@ import uk.ac.ukc.iscream.util.*;
  * actually contains some elements.
  *
  * @author  $Author: tdb $
- * @version $Id: Queue.java,v 1.8 2001/01/30 02:12:23 tdb Exp $
+ * @version $Id: Queue.java,v 1.14 2001/03/01 01:05:49 tdb Exp $
  */
 public class Queue {
 
@@ -22,11 +23,59 @@ public class Queue {
     /**
      * The current CVS revision of this class
      */
-    public static final String REVISION = "$Revision: 1.8 $";
+    public static final String REVISION = "$Revision: 1.14 $";
     
+    /**
+     * Pass to constructor to remove a RANDOM item from
+     * the Queue upon reaching the maximum limit.
+     */
+    public static final int RANDOM = 0;
+    
+    /**
+     * Pass to constructor to remove the FIRST item from
+     * the Queue upon reaching the maximum limit.
+     */
+    public static final int FIRST = 1;
+    
+    /**
+     * Pass to constructor to remove the LAST item from
+     * the Queue upon reaching the maximum limit.
+     */
+    public static final int LAST = 2;
+    
+    /**
+     * Pass to constructor to drop the new item upon reaching
+     * the maximum Queue limit.
+     */
+    public static final int DROP = 3;
+    
 //---STATIC METHODS---
 
 //---CONSTRUCTORS---  
+    
+    /**
+     * Constructs a new Queue with a maximum size limit on
+     * any individual queue. This should be used to stop
+     * conditions where the Queue cannot be guaranteed to
+     * be emptied as quick as it's filled.
+     *
+     * An algorithm will be used to remove data when new data
+     * arrives. There may be choices of algorithms later on.
+     *
+     * @param maxSize the upper limit for a queue
+     * @param removeAlgorithm the remove algorithm to use upon reaching the maxSize
+     */
+    public Queue(int maxSize, int removeAlgorithm) {
+        _maxSize = maxSize;
+        _removeAlgorithm = removeAlgorithm;
+    }
+    
+    /**
+     * Constructs a Queue with no maximum size.
+     */
+    public Queue() {
+        _maxSize = -1;
+    }
 
 //---PUBLIC METHODS---
     
@@ -40,11 +89,21 @@ public class Queue {
         for(int i=0; i < _lists.size(); i++) {
             // skip over any gaps left in the list
             if(_lists.get(i) != null) {
+                // get size before adding to the Queue
                 int s = ((LinkedList) _lists.get(i)).size();
-                synchronized(this) {
-                    // add() does the same thing, but this ensures behaviour
-                    ((LinkedList) _lists.get(i)).addLast(o);
+                // check whether we need to remove an item from the current Queue
+                if(_maxSize!=-1 && s==_maxSize && _removeAlgorithm!=DROP) {
+                    // we need to remove an item
+                    removeQueueItem((LinkedList) _lists.get(i));
                 }
+                // check if we should add (not if Queue full, and using DROP algorithm)
+                if(!(s==_maxSize && _removeAlgorithm==DROP)) {
+                    // add the next item, ensuring we lock
+                    synchronized(this) {
+                        // LinkedList.add() does the same thing, but this ensures behaviour
+                        ((LinkedList) _lists.get(i)).addLast(o);
+                    }
+                }
                 // if the queue was empty before the add it is possible
                 // that a consumer is waiting... so we notify them
                 if (s == 0) {
@@ -119,28 +178,30 @@ public class Queue {
     }
     
     /**
-     * This method returns a textual status of the queues. It
-     * is merely for observation, and would most likely be used
-     * by a larger "monitoring" component. Information returned
-     * includes the current size of each queue, and the total
-     * items passed through.
+     * This method returns an XML textual status of the queues.
+     * It is merely for observation, and would most likely be
+     * used by a larger "monitoring" component. Information
+     * returned includes the current size of each queue, and
+     * the total items passed through.
      *
-     * @return A String message containing status information.
+     * @return A String message containing status information in XML format
      */
-    public String status() {
-        String status = "";
+    public String xmlStatus() {
+        String status = "<queue ";
         for(int i=0; i < _lists.size(); i++) {
             // check for null entries
             if(_lists.get(i) != null) {
-                status += "Queue number "+i+" contains "+((LinkedList) _lists.get(i)).size()+" elements";
-                status += "\n";
+                status += "queue"+i+"=\""+((LinkedList) _lists.get(i)).size()+"\" ";
             }
             else {
-                status += "Slot number "+i+" is currently empty";
-                status += "\n";
+                status += "queue"+i+"=\"[deleted]\" ";
             }
         }
-        status += "A total of "+_count+" elements have been added to the queues";
+        status += "total=\""+_count+"\"";
+        if(_maxSize != -1) {
+            status += " maxSize=\""+_maxSize+"\"";
+        }
+        status += "</queue>";
         return status;
     }
     
@@ -210,6 +271,59 @@ public class Queue {
     }
     
     /**
+     * Start a monitor on our own Queue. This will log XML
+     * statistics about our Queue to a given Queue (could be
+     * the one being monitored).
+     *
+     * @param interval The long interval, in milliseconds, at which to take samples
+     * @param destQueue The queue to monitor to
+     * @param name A name to identify this Queue with
+     * @return whether we succeeded
+     */
+    public boolean startMonitor(long interval, Queue destQueue, String name) {
+        if(_queueMon == null) {
+            // start a monitor
+            _queueMon = new QueueMonitor(this, destQueue, interval, name);
+            _queueMon.start();
+            return true;
+        }
+        else {
+            // already have a monitor running
+            return false;
+        }
+    }
+    
+    /**
+     * Start a monitor on our own Queue. This will log XML
+     * statistics about our Queue to this Queue.
+     *
+     * @param interval The long interval, in milliseconds, at which to take samples
+     * @param name A name to identify this Queue with
+     * @return whether we succeeded
+     */
+    public boolean startMonitor(long interval, String name) {
+        return startMonitor(interval, this, name);
+    }
+    
+    /**
+     * Stop a monitor on our Queue if we have on running.
+     *
+     * @return whether we succeeded
+     */
+    public boolean stopMonitor() {
+        if(_queueMon != null) {
+            // stop a monitor
+            _queueMon.shutdown();
+            _queueMon = null;
+            return true;
+        }
+        else {
+            // no monitor running
+            return false;
+        }
+    }
+    
+    /**
      * Overrides the {@link java.lang.Object#toString() Object.toString()}
      * method to provide clean logging (every class should have this).
      *
@@ -226,7 +340,38 @@ public class Queue {
     }
 
 //---PRIVATE METHODS---
-
+    
+    /**
+     * This method removes an item from a Queue, using a method
+     * requested at construction.
+     *
+     * @param list The LinkedList from which to remove an item.
+     */
+    private void removeQueueItem(LinkedList list) {
+        // look at our algorithm
+        // remove a random item from the list
+        if(_removeAlgorithm==RANDOM) {
+            // new Random, with a good seed
+            Random rand = new Random(System.currentTimeMillis());
+            int i = rand.nextInt(_maxSize);
+            synchronized(this) {
+                list.remove(i);
+            }
+        }
+        // remove the first item from the list
+        else if(_removeAlgorithm==FIRST) {
+            synchronized(this) {
+                list.removeFirst();
+            }
+        }
+        // remove the last item from the list
+        else if(_removeAlgorithm==LAST) {
+            synchronized(this) {
+                list.removeLast();
+            }
+        }
+    }
+    
 //---ACCESSOR/MUTATOR METHODS---
 
 //---ATTRIBUTES---
@@ -241,6 +386,22 @@ public class Queue {
      * passed through, for statistical purposes.
      */
     private int _count = 0;
+    
+    /**
+     * A reference to our QueueMonitor, if we have one.
+     */
+    private QueueMonitor _queueMon = null;
+    
+    /**
+     * The maximum size of any Queue.
+     */
+    private int _maxSize = -1;
+    
+    /**
+     * The remove algorithm to use upon a Queue reaching
+     * it's maximum size.
+     */
+    private int _removeAlgorithm = -1;
     
     /**
      * This is the friendly identifier of the