rate limit notification enqueues
This is distinct from and in addition to the limit on the number of
distinct notifications. This includes many updates to a single
notification.
Bug: 28693065
Change-Id: I5ec0911716cace91d3ad85435a5c6123b290b3a2
diff --git a/services/core/java/com/android/server/notification/RateEstimator.java b/services/core/java/com/android/server/notification/RateEstimator.java
new file mode 100644
index 0000000..4dc30a4
--- /dev/null
+++ b/services/core/java/com/android/server/notification/RateEstimator.java
@@ -0,0 +1,54 @@
+/*
+ * Copyright (C) 2016 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 com.android.server.notification;
+
+
+/**
+ * Exponentially weighted moving average estimator for event rate.
+ *
+ * {@hide}
+ */
+public class RateEstimator {
+ private static final double RATE_ALPHA = 0.8;
+ private static final double MINIMUM_DT = 0.0005;
+ private long mLastEventTime;
+ private float mInterarrivalTime;
+
+ public RateEstimator(long now) {
+ mLastEventTime = now;
+ }
+
+ /** Update the estimate to account for an event that jsut happened. */
+ public float update(long now) {
+ mInterarrivalTime = (float) getInterarrivalEstimate(now);
+ mLastEventTime = now;
+ return (float) (1.0 / mInterarrivalTime);
+ }
+
+ /** @return the estimated rate if there were a new event right now. */
+ public float getRate(long now) {
+ return (float) (1.0 / getInterarrivalEstimate(now));
+ }
+
+ /** @return the average inter-arrival time if there were a new event right now. */
+ private double getInterarrivalEstimate(long now) {
+ // a*iat_old + (1-a)*(t_now-t_last)
+ double dt = ((double) (now - mLastEventTime)) / 1000.0;
+ dt = Math.max(dt, MINIMUM_DT);
+ return (RATE_ALPHA * mInterarrivalTime + (1.0 - RATE_ALPHA) * dt);
+ }
+}