downloads: Improve download rate estimation.

content/browser/download/rate_estimator.h

+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CONTENT_BROWSER_DOWNLOAD_RATE_ESTIMATOR_H_
+#define CONTENT_BROWSER_DOWNLOAD_RATE_ESTIMATOR_H_
+
+#include <string>
+#include <vector>
+
+#include "base/basictypes.h"
+#include "base/time.h"
+#include "content/common/content_export.h"
+
+namespace content {
+
+// RateEstimator generates rate estimates based on recent activity.
+//
+// Internally it uses a fixed-size ring buffer, and develops estimates
+// based on a small sliding window of activity.
+class CONTENT_EXPORT RateEstimator {
+ public:
+  RateEstimator();
+  RateEstimator(base::TimeDelta bucket_time,
+                size_t num_buckets,
+                base::TimeTicks now);
+  ~RateEstimator();
+
+  // Increment the counter by |count|. The first variant uses the current time,
+  // the second variant provides the time that |count| is observed.
+  void Increment(uint32 count);
+  void Increment(uint32 count, base::TimeTicks now);
+
+  // Get a rate estimate, in terms of counts/second. The first variant uses the
+  // current time, the second variant provides the time.
+  uint64 GetCountPerSecond() const;
+  uint64 GetCountPerSecond(base::TimeTicks now) const;
+
+ private:
+  void ClearOldBuckets(base::TimeTicks now);
+  void ResetBuckets(base::TimeTicks now);
+
+  std::vector<uint32> history_;
+  base::TimeDelta bucket_time_;
+  size_t oldest_index_;
+  size_t bucket_count_;
+  base::TimeTicks oldest_time_;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_DOWNLOAD_RATE_ESTIMATOR_H_