Pull cacheinvalidations code directory into chromium repo.

third_party/cacheinvalidation/src/java/com/google/ipc/invalidation/util/Smearer.java

+/*
+ * Copyright 2011 Google Inc.
+ *
+ * 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.google.ipc.invalidation.util;
+
+import java.util.Random;
+
+/**
+ * An abstraction to "smear" values by a given percent. Useful for randomizing delays a little bit
+ * so that (say) processes do not get synchronized on time inadvertently, e.g., a heartbeat task
+ * that sends a message every few minutes is smeared so that all clients do not end up sending a
+ * message at the same time. In particular, given a {@code delay}, returns a value that is randomly
+ * distributed between [delay - smearPercent * delay, delay + smearPercent * delay]
+ *
+ */
+public class Smearer {
+
+  private final Random random;
+
+  /** The percentage (0, 1.0] for smearing the delay. */
+  private double smearFraction;
+
+  /**
+   * Creates a smearer with the given random number generator. If {@code smearPercent} is 0, uses an
+   * internal default for smearing.
+   * <p>
+   * REQUIRES: 0 < smearPercent <= 100
+   */
+  public Smearer(Random random, final int smearPercent) {
+    Preconditions.checkState((smearPercent >= 0) && (smearPercent <= 100));
+    this.random = random;
+    this.smearFraction = smearPercent / 100.0;
+  }
+
+  /**
+   * Given a {@code delay}, returns a value that is randomly distributed between
+   * [delay - smearPercent * delay, delay + smearPercent * delay]
+   */
+  public int getSmearedDelay(int delay) {
+    // Get a random number between -1 and 1 and then multiply that by the smear
+    // fraction.
+    double smearFactor = (2 * random.nextDouble() - 1.0) * smearFraction;
+    return (int) Math.ceil(delay + delay * smearFactor);
+  }
+}