Code to reuse PlatformAddress objects. Minimizing garbage creation on the framework...

2nd version: complete rewrite using 8 bit hash, up to 5 probes, cycle through probes cache replacement. (Thank you MichaelDt for your help.)
- 1st amend: applied requested modifications
- 2nd amend: comment openers, curly bracket

diff --git a/libcore/luni/src/main/java/org/apache/harmony/luni/platform/PlatformAddressFactory.java b/libcore/luni/src/main/java/org/apache/harmony/luni/platform/PlatformAddressFactory.java
index 5c31980..9ec0fcd 100644 (file)
--- a/libcore/luni/src/main/java/org/apache/harmony/luni/platform/PlatformAddressFactory.java
+++ b/libcore/luni/src/main/java/org/apache/harmony/luni/platform/PlatformAddressFactory.java
@@ -24,13 +24,61 @@ import java.io.IOException;
 
 public class PlatformAddressFactory {
 
-    public static PlatformAddress on(int value) {
-        return PlatformAddressFactory.on(value, PlatformAddress.UNKNOWN);
+    // BEGIN android-added
+    /**
+     * Defines the number of PlatformAddress objects to be cached. Must be a
+     * power of two. Caching PlatformAddress objects minimizes the creation
+     * of garbage and reduces the number of GC-hiccups in OpenGL animations.
+     */
+    private final static int CACHE_SIZE = 1<<8;
+
+    /**
+     * A mask with all bits set, matching the size of the cache.
+     */
+    private final static int CACHE_MASK = CACHE_SIZE - 1;
+
+    /**
+     * Defines the maximum number of probes taken per hash, used for looking
+     * up an empty cache slot or a previously stored PlatformAddress.
+     */
+    private final static int MAX_PROBES = 5;
+
+    /**
+     * A cycling index (0 to MAX_PROBES-1) used to replace elements in the cache.
+     */
+    private static int replacementIndex = 0;
+
+    /**
+     * Array of PlatformAddress references kept from garbage collection.
+     */
+    private static PlatformAddress[] cache = new PlatformAddress[CACHE_SIZE];
+    // END android-added
+
+
+    // BEGIN android-changed
+    public synchronized static PlatformAddress on(int value, long size) {
+        if (value == 0) {
+            return PlatformAddress.NULL;
+        }
+        int idx = value >> 5;
+        for (int probe = 0; probe < MAX_PROBES; probe++) {
+            PlatformAddress cachedObj = cache[(idx + probe) & CACHE_MASK];
+            if (cachedObj == null) {
+                return cache[(idx + probe) & CACHE_MASK] =
+                    new PlatformAddress(value, size);
+            }
+            if (cachedObj.osaddr == value && cachedObj.size == size) {
+                return cachedObj;
+            }
+        }
+        replacementIndex = (replacementIndex + 1) % MAX_PROBES;
+        return cache[(idx + replacementIndex) & CACHE_MASK] =
+            new PlatformAddress(value, size);
     }
+    // END android-changed
 
-    public static PlatformAddress on(int value, long size) {
-        PlatformAddress addr = (value == 0) ? PlatformAddress.NULL : new PlatformAddress(value, size);
-        return addr;
+    public static PlatformAddress on(int value) {
+        return PlatformAddressFactory.on(value, PlatformAddress.UNKNOWN);
     }
 
     public static MappedPlatformAddress mapOn(int value, long size) {