Tracked objects. Now to set about to figuring out what to track.

git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@3075 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/java/com/threerings/util/TrackedObject.java

@@ -0,0 +1,75 @@
+//
+// $Id: TrackedObject.java,v 1.1 2004/08/13 23:44:16 mdb Exp $
+
+package com.threerings.util;
+
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.Map;
+
+import com.samskivert.util.Tuple;
+
+/**
+ * Used to perform rudimentary memory profiling on large, running systems
+ * where it is impractical to operate a real profiler. Instances of {@link
+ * TrackedObject} record their existence when constructed and their
+ * destruction when finalized which, combined with periodic queries of the
+ * current total object count (by class) logged and graphed (gnuplot is
+ * your friend), can provide an indication of systems that are improperly
+ * retaining references.
+ */
+public class TrackedObject
+{
+    /** Records that this object came into existence. */
+    public TrackedObject ()
+    {
+        Class clazz = getClass();
+        synchronized (_map) {
+            int[] count = (int[])_map.get(clazz);
+            if (count == null) {
+                _map.put(clazz, count = new int[1]);
+            }
+            count[0]++;
+        }
+    }
+
+    /** Records that this object was collected. */
+    protected void finalize ()
+    {
+        Class clazz = getClass();
+        synchronized (_map) {
+            int[] count = (int[])_map.get(clazz);
+            if (count != null) {
+                count[0]--;
+            } else {
+                Log.warning("Finalized TrackedObject missing counter! " +
+                            "[class=" + clazz + "].");
+            }
+        }
+    }
+
+    /**
+     * Returns a {@link Tuple} containing an array of {@link Class}
+     * instances and an <code>int[]</code> array that represent the number
+     * of outstanding instance of all {@link TrackedObject}s in the VM.
+     */
+    public static Tuple getSnapshot ()
+    {
+        Class[] classes = null;
+        int[] counts = null;
+        synchronized (_map) {
+            classes = new Class[_map.size()];
+            counts = new int[_map.size()];
+            Iterator iter = _map.entrySet().iterator();
+            for (int ii = 0; iter.hasNext(); ii++) {
+                Map.Entry entry = (Map.Entry)iter.next();
+                classes[ii] = (Class)entry.getKey();
+                counts[ii] = ((int[])entry.getValue())[0];
+            }
+        }
+        return new Tuple(classes, counts);
+    }
+
+    /** Tracks a mapping from {@link Class} object to active count. */
+    protected static HashMap _map = new HashMap();
+}