--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/ShenandoahVisualizer.java	Wed Dec 14 16:34:10 2016 +0100
@@ -0,0 +1,203 @@
+/*
+ * Copyright (c) 2016, Red Hat, Inc. and/or its affiliates.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+import java.awt.*;
+import java.awt.event.*;
+import java.awt.image.*;
+import javax.swing.*;
+import java.util.*;
+import sun.jvmstat.monitor.*;
+
+class ShenandoahVisualizer {
+
+    private static final int USED_MASK = 0x3fffffff;
+    private static final int USED_SHIFT = 0;
+    private static final int LIVE_MASK = 0x3fffffff;
+    private static final int LIVE_SHIFT = 30;
+    private static final int FLAGS_MASK = 0xf;
+    private static final int FLAGS_SHIFT = 60;
+
+    private static final int WIDTH = 1000;
+    private static final int HEIGHT = 800;
+    static BufferedImage img;
+    static boolean isMarking;
+    static boolean isEvacuating;
+
+    static boolean doRepaint = true;
+
+    static class VisPanel extends JPanel {
+        public void paint(Graphics g) {
+            if (img != null) {
+                synchronized (ShenandoahVisualizer.class) {
+                    g.drawImage(img, 0, 0, this);
+                }
+            }
+        }
+    }
+
+    static class StatusPanel extends JPanel {
+        public void paint(Graphics g) {
+            g.setColor(Color.BLACK);
+            g.drawString("marking:", 0, 15);
+            if (isMarking) {
+                g.setColor(Color.RED);
+            } else {
+                g.setColor(Color.GREEN);
+            }
+            g.fillRect(60, 0, 40, 20);
+
+            g.setColor(Color.BLACK);
+            g.drawString("evacuating:", 120, 15);
+            if (isEvacuating) {
+                g.setColor(Color.RED);
+            } else {
+                g.setColor(Color.GREEN);
+            }
+            g.fillRect(220, 0, 40, 20);
+            
+        }
+    }
+
+    static class VisPanelListener extends ComponentAdapter {
+        public void componentResized(ComponentEvent ev) {
+            // System.out.println("resizing to: " + ev.getComponent().getWidth() + "x" + ev.getComponent().getHeight());
+            img = new BufferedImage(ev.getComponent().getWidth(), ev.getComponent().getHeight(), BufferedImage.TYPE_INT_RGB);
+        }
+    }
+
+    public static void main(String[] args) throws Exception {
+        if (args.length < 1) {
+            System.err.println("missing VM identifier");
+            System.exit(-1);
+        }
+        MonitoredHost host = MonitoredHost.getMonitoredHost(args[0]);
+        MonitoredVm vm = host.getMonitoredVm(new VmIdentifier(args[0]));
+        LongMonitor max_regions_mon = (LongMonitor) vm.findByName("sun.gc.shenandoah.regions.max_regions");
+        int max_regions = (int) max_regions_mon.longValue();
+        LongMonitor max_size_mon = (LongMonitor) vm.findByName("sun.gc.shenandoah.regions.region_size");
+        long max_size = max_size_mon.longValue();
+        LongMonitor status_mon = (LongMonitor) vm.findByName("sun.gc.shenandoah.regions.status");
+
+        System.out.println("max_regions: " + max_regions);
+        LongMonitor[] mons_data = new LongMonitor[max_regions];
+        for (int i = 0; i < max_regions; i++) {
+            mons_data[i] = (LongMonitor) vm.findByName("sun.gc.shenandoah.regions.region." + i + ".data");
+            //System.out.println("region " + i + " used: " + mons[i].longValue());
+        }
+
+        img = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
+        VisPanel p = new VisPanel();
+        p.addComponentListener(new VisPanelListener());
+
+        StatusPanel statusPanel = new StatusPanel();
+        statusPanel.setPreferredSize(new Dimension(220, 20));
+
+        JFrame frame = new JFrame();
+        frame.getContentPane().add(p, BorderLayout.CENTER);
+        frame.getContentPane().add(statusPanel, BorderLayout.SOUTH);
+        frame.setSize(WIDTH, HEIGHT);
+        frame.setVisible(true);
+        frame.addWindowListener(new WindowAdapter() {
+                public void windowClosing(WindowEvent e) {
+                    doRepaint = false;
+                }
+            });
+        int cols = (int) Math.floor(Math.sqrt(max_regions));
+        int rows = (int) Math.floor(max_regions / cols);
+        while (doRepaint) {
+            long start = System.currentTimeMillis();
+            synchronized (ShenandoahVisualizer.class) {
+                isMarking = (status_mon.longValue() & 0x1) > 0;
+                isEvacuating = (status_mon.longValue() & 0x2) > 0;
+
+                int rectWidth = img.getWidth() / cols;
+                int rectHeight = img.getHeight() / rows;
+                Graphics g = img.getGraphics();
+                for (int i = 0; i < max_regions; i++) {
+                    int rectx = (i % cols) * rectWidth;
+                    int recty = (i / rows) * rectHeight;
+
+                    if (mons_data[i] == null) {
+                        System.err.println("Insufficient shared memory for all region counters. Try -XX:PerfDataMemorySize=512K or higher when running the monitored program.");
+                        System.exit(-1);
+                    }
+
+                    long data = mons_data[i].longValue();
+                    long used = (data >>> USED_SHIFT) & USED_MASK;
+                    int usedLvl = Math.min(255, (int) (used * 255 / max_size));
+
+                    long live = (data >>> LIVE_SHIFT) & LIVE_MASK;
+                    int liveLvl = Math.min(255, (int) (live * 255 / max_size));
+
+                    long stat = (data >>> FLAGS_SHIFT) & FLAGS_MASK;
+                    boolean inCset = (stat & 0x1) > 0;
+                    boolean humongous = (stat & 0x2) > 0;
+                    boolean unused = (stat & 0x4) > 0;
+
+                    g.setColor(Color.WHITE);
+                    g.fillRect(rectx, recty, rectWidth, rectHeight);
+
+                    g.setColor(new Color(150, 150, 150));
+                    g.fillRect(rectx, recty, rectWidth * usedLvl / 255, rectHeight);
+
+                    g.setColor(new Color(0, 200, 0));
+                    g.fillRect(rectx, recty, rectWidth * liveLvl / 255, rectHeight);
+
+                    g.setColor(new Color(0, 100, 0));
+                    g.drawLine(rectx + rectWidth * liveLvl / 255, recty, rectx + rectWidth * liveLvl / 255, recty + rectHeight);
+
+                    if (inCset) {
+			g.setColor(new Color(255, 255, 0));
+			g.fillRect(rectx, recty, rectWidth, rectHeight / 3);
+                	g.setColor(Color.BLACK);
+			g.drawRect(rectx, recty, rectWidth, rectHeight / 3);
+                    }
+
+                    if (humongous) {
+			g.setColor(new Color(255, 0, 0));
+			g.fillRect(rectx, recty, rectWidth, rectHeight / 3);
+                	g.setColor(Color.BLACK);
+			g.drawRect(rectx, recty, rectWidth, rectHeight / 3);
+                    }
+
+                    if (unused) {
+			g.setColor(new Color(0, 0, 0));
+                        g.drawLine(rectx, recty, rectx + rectWidth, recty + rectHeight);
+                        g.drawLine(rectx, recty + rectHeight, rectx + rectWidth, recty);
+                    }
+                    g.setColor(Color.BLACK);
+                    g.drawRect(rectx, recty, rectWidth, rectHeight);
+                }
+                g.dispose();
+            }
+            long duration = System.currentTimeMillis() - start;
+            long sleep = 100 - duration;
+            if (sleep > 0) {
+                Thread.sleep(sleep);
+            }
+            frame.repaint();
+        }
+        frame.dispose();
+    }
+}
+