help class that simplifies effective handling of high rate events, that otherwise might flood the event queue

tools/cooja/java/se/sics/cooja/dialogs/UpdateAggregator.java

@@ -0,0 +1,137 @@
+/*
+ * Copyright (c) 2010, Swedish Institute of Computer Science. All rights
+ * reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * 1. Redistributions of source code must retain the above copyright notice,
+ * this list of conditions and the following disclaimer. 2. Redistributions in
+ * binary form must reproduce the above copyright notice, this list of
+ * conditions and the following disclaimer in the documentation and/or other
+ * materials provided with the distribution. 3. Neither the name of the
+ * Institute nor the names of its contributors may be used to endorse or promote
+ * products derived from this software without specific prior written
+ * permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * $Id: UpdateAggregator.java,v 1.1 2010/03/26 09:27:58 fros4943 Exp $
+ */
+
+package se.sics.cooja.dialogs;
+
+import java.awt.EventQueue;
+import java.awt.event.ActionEvent;
+import java.awt.event.ActionListener;
+import java.util.ArrayList;
+import java.util.List;
+
+import javax.swing.Timer;
+
+import se.sics.cooja.plugins.LogListener;
+
+/**
+ * Help class to avoid EventQueue flooding by aggregating several update events.
+ * 
+ * To be used by plugins et. al. that receive updates at a high rate 
+ * (such as new Log Output messages), and must handle them from the Event thread.
+ * 
+ * @author Fredrik Osterlind, Niclas Finne
+ *
+ * @param <A> Event whose update event are aggregated
+ * @see LogListener
+ */
+public abstract class UpdateAggregator<A> {
+  private static final int DEFAULT_MAX_PENDING = 256;
+  private int maxPending;
+  
+  private ArrayList<A> pending;
+  private Timer t;
+
+  /**
+   * @param interval Max interval (ms)
+   */
+  public UpdateAggregator(int interval) {
+    this(interval, DEFAULT_MAX_PENDING);
+  }
+  /**
+   * @param delay Max interval (ms)
+   * @param maxEvents Max pending events (default 256)
+   */
+  public UpdateAggregator(int interval, int maxEvents) {
+    this.maxPending = maxEvents;
+    pending = new ArrayList<A>();
+    t = new Timer(interval, new ActionListener() {
+      public void actionPerformed(ActionEvent e) {
+        consume.run();
+      }
+    });
+    t.setInitialDelay(0);
+    t.setCoalesce(true);
+    t.setRepeats(true);
+  }
+
+  /**
+   * Consumer: called from event queue
+   */
+  private Runnable consume = new Runnable() {
+    public void run() {
+      if (pending.isEmpty()) {
+        return;
+      };
+
+      List<A> q = getPending();
+      if (q != null) {
+        /* Handle objects */
+        handle(q);
+      }
+
+      synchronized (UpdateAggregator.this) {
+        UpdateAggregator.this.notifyAll();
+      }
+    }
+  };
+  
+  /**
+   * @param l All events since last update
+   */
+  protected abstract void handle(List<A> l);
+  
+  private synchronized List<A> getPending() {
+    /* Queue pending packets */
+    ArrayList<A> tmp = pending;
+    pending = new ArrayList<A>();
+    return tmp;
+  }
+
+  /**
+   * @param a Add new event (any thread). May block.
+   */
+  public synchronized void add(A a) {
+    try {
+      while (pending.size() > maxPending) {
+        /* Delay producer thread; events are coming in too fast */
+        EventQueue.invokeLater(consume); /* Request immediate consume */
+        wait();
+      }
+    } catch (InterruptedException e) {
+    }
+    pending.add(a);
+  }
+
+  public void start() {
+    t.start();
+  }
+  public void stop() {
+    t.stop();
+  }
+}