1 files changed, 94 insertions, 0 deletions
diff --git a/core/java/android/os/LatencyTimer.java b/core/java/android/os/LatencyTimer.java
new file mode 100644
index 0000000..ed2f0f9e
--- /dev/null
+++ b/core/java/android/os/LatencyTimer.java
@@ -0,0 +1,94 @@
+/*
+ * Copyright (C) 2009 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.os;
+
+import android.util.Log;
+
+import java.util.HashMap;
+
+/**
+ * A class to help with measuring latency in your code.
+ * 
+ * Suggested usage:
+ * 1) Instanciate a LatencyTimer as a class field.
+ *      private [static] LatencyTimer mLt = new LatencyTimer(100, 1000);
+ * 2) At various points in the code call sample with a string and the time delta to some fixed time.
+ *    The string should be unique at each point of the code you are measuring.
+ *      mLt.sample("before processing event", System.nanoTime() - event.getEventTimeNano());
+ *      processEvent(event);
+ *      mLt.sample("after processing event ", System.nanoTime() - event.getEventTimeNano());
+ *
+ * @hide
+ */
+public final class LatencyTimer
+{
+    final String TAG = "LatencyTimer";
+    final int mSampleSize;
+    final int mScaleFactor;
+    volatile HashMap<String, long[]> store = new HashMap<String, long[]>();
+
+    /**
+    * Creates a LatencyTimer object
+    * @param sampleSize number of samples to collect before printing out the average
+    * @param scaleFactor divisor used to make each sample smaller to prevent overflow when
+    *        (sampleSize * average sample value)/scaleFactor > Long.MAX_VALUE
+    */
+    public LatencyTimer(int sampleSize, int scaleFactor) {
+        if (scaleFactor == 0) {
+            scaleFactor = 1;
+        }
+        mScaleFactor = scaleFactor;
+        mSampleSize = sampleSize;
+    }
+
+    /**
+     * Add a sample delay for averaging.
+     * @param tag string used for printing out the result. This should be unique at each point of
+     *  this called.
+     * @param delta time difference from an unique point of reference for a particular iteration
+     */
+    public void sample(String tag, long delta) {
+        long[] array = getArray(tag);
+
+        // array[mSampleSize] holds the number of used entries
+        final int index = (int) array[mSampleSize]++;
+        array[index] = delta;
+        if (array[mSampleSize] == mSampleSize) {
+            long totalDelta = 0;
+            for (long d : array) {
+                totalDelta += d/mScaleFactor;
+            }
+            array[mSampleSize] = 0;
+            Log.i(TAG, tag + " average = " + totalDelta / mSampleSize);
+        }
+    }
+
+    private long[] getArray(String tag) {
+        long[] data = store.get(tag);
+        if (data == null) {
+            synchronized(store) {
+                data = store.get(tag);
+                if (data == null) {
+                    data = new long[mSampleSize + 1];
+                    store.put(tag, data);
+                    data[mSampleSize] = 0;
+                }
+            }
+        }
+        return data;
+    }
+}