Amortize data usage using TrafficStats on Android.

components/data_usage/android/traffic_stats_amortizer.h

Index: components/data_usage/android/traffic_stats_amortizer.h
diff --git a/components/data_usage/android/traffic_stats_amortizer.h b/components/data_usage/android/traffic_stats_amortizer.h
new file mode 100644
index 0000000000000000000000000000000000000000..17ec8c73dab410dd820410ca694a6cb98ea2cd97
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+++ b/components/data_usage/android/traffic_stats_amortizer.h
@@ -0,0 +1,137 @@
+// Copyright 2015 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 COMPONENTS_DATA_USAGE_ANDROID_TRAFFIC_STATS_AMORTIZER_H_
+#define COMPONENTS_DATA_USAGE_ANDROID_TRAFFIC_STATS_AMORTIZER_H_
+
+#include <stdint.h>
+
+#include <utility>
+#include <vector>
+
+#include "base/macros.h"
+#include "base/memory/linked_ptr.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+#include "base/threading/thread_checker.h"
+#include "base/time/time.h"
+#include "components/data_usage/core/data_use_amortizer.h"
+
+namespace base {
+class TickClock;
+class Timer;
+}
+
+namespace data_usage {
+
+struct DataUse;
+
+namespace android {
+
+// Class that uses Android TrafficStats to amortize any unincluded overhead into
+// the data usage reported by the network stack. Should only be used on the IO
+// thread. Only one TrafficStatsAmortizer should be active globally at a time,
+// since TrafficStats measurements are global for the entire application, so
+// having multiple active TrafficStatsAmortizers at a time would cause each of
+// them to overestimate the overhead here.
+class TrafficStatsAmortizer : public DataUseAmortizer {
+ public:
+  TrafficStatsAmortizer();
+  ~TrafficStatsAmortizer() override;
+
+  void AmortizeDataUse(scoped_ptr<DataUse> data_use,

[tbansal1, 2015/11/10 18:53:55]

Method comments please.

[sclittle, 2015/11/11 02:10:07]

Done.

+                       const DataUseConsumerCallback& callback) override;
+
+  void OnExtraBytes(int64_t extra_tx_bytes, int64_t extra_rx_bytes) override;
+
+  base::WeakPtr<TrafficStatsAmortizer> GetWeakPtr();
+
+ protected:
+  // Constructor for testing purposes, allowing for tests to take full control
+  // over the timing of the TrafficStatsAmortizer and the byte counts returned
+  // from TrafficStats. |traffic_stats_query_timer| must not be a repeating
+  // timer.
+  TrafficStatsAmortizer(scoped_ptr<base::TickClock> tick_clock,
+                        scoped_ptr<base::Timer> traffic_stats_query_timer,
+                        const base::TimeDelta& traffic_stats_query_delay,
+                        const base::TimeDelta& max_amortization_delay,
+                        size_t max_data_use_buffer_size);
+
+  // Query the total transmitted and received bytes for the application from
+  // TrafficStats. Stores the byte counts in |tx_bytes| and |rx_bytes|
+  // respectively and returns true if both values are available from
+  // TrafficStats, otherwise returns false.
+  // Virtual for testing.
+  virtual bool QueryTrafficStats(int64_t* tx_bytes, int64_t* rx_bytes) const;
+
+ private:
+  void AddPreAmortizationBytes(int64_t tx_bytes, int64_t rx_bytes);

[bengr, 2015/11/10 18:12:50]

Please comment on what this and AmortizeNow() do.

[sclittle, 2015/11/11 02:10:07]

Done.

+
+  void AmortizeNow();
+
+  base::ThreadChecker thread_checker_;
+
+  // TickClock for determining the current time tick.
+  scoped_ptr<base::TickClock> tick_clock_;
+
+  // One-shot timer for polling TrafficStats byte counts until they stabilize.

[bengr, 2015/11/10 18:12:50]

Please document the algorithm for taking TrafficStats measurements.

[sclittle, 2015/11/11 02:10:07]

Done. This comment was wrong.

+  // This must not be a repeating timer.
+  scoped_ptr<base::Timer> traffic_stats_query_timer_;
+
+  // The delay between polls of TrafficStats byte counts for waiting for the
+  // TrafficStats byte counts to stabilize.

[bengr, 2015/11/10 18:12:50]

What does "stabilize" mean?

[sclittle, 2015/11/11 02:10:07]

Oops, I forgot to update this and a few other comments here. Fixed.

+  const base::TimeDelta traffic_stats_query_delay_;
+
+  // The maximum amount of time that the TrafficStatsAmortizer is allowed to
+  // spend waiting to do an amortization run.
+  const base::TimeDelta max_amortization_delay_;
+
+  // The maximum allowed size of the |buffered_data_use_| buffer before DataUse
+  // elements start to be passed through without performing any amortization.

[bengr, 2015/11/10 18:12:50]

Why is this needed?

[sclittle, 2015/11/11 02:10:07]

Added comment. It's here so that we don't hog memory with the buffer - DataUse
objects could easily take around 1 KB in memory each, so that could get pretty
big if we're not careful.

+  const size_t max_data_use_buffer_size_;
+
+  // Indicates whether or not the TrafficStatsAmortizer currently has
+  // pre-amortization bytes waiting for amortization to be performed.
+  bool is_amortization_run_in_progress_;
+
+  // The time when the first pre-amortization bytes for the current amortization
+  // run were given to this TrafficStatsAmortizer.
+  base::TimeTicks current_amortization_run_start_time_;
+
+  // Buffer of pre-amortization data use that has accumulated since the last
+  // time amortization was performed, paired with the callbacks for each DataUse
+  // object. Nothing but |buffered_data_use_| is allowed to hold linked_ptrs to
+  // the DataUse objects, so that these linked_ptrs can be released later.
+  std::vector<std::pair<linked_ptr<DataUse>, DataUseConsumerCallback>>
+      buffered_data_use_;
+
+  // Indicates if TrafficStats byte counts were available during the last time
+  // amortization was performed.
+  bool are_last_amortization_traffic_stats_available_;
+  // The total transmitted bytes according to TrafficStats during the last time
+  // amortization was performed, if they were available.
+  int64_t last_amortization_traffic_stats_tx_bytes_;
+  // The total received bytes according to TrafficStats during the last time
+  // amortization was performed, if they were available.
+  int64_t last_amortization_traffic_stats_rx_bytes_;
+
+  // Total pre-amortization transmitted bytes since the last time amortization
+  // was performed, including bytes from |buffered_data_use_| and any extra
+  // bytes that were added.
+  int64_t pre_amortization_tx_bytes_;
+
+  // Total pre-amortization received bytes since the last time amortization was
+  // performed, including bytes from |buffered_data_use_| and any extra bytes
+  // that were added.
+  int64_t pre_amortization_rx_bytes_;
+
+  base::WeakPtrFactory<TrafficStatsAmortizer> weak_ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(TrafficStatsAmortizer);
+};
+
+}  // namespace android
+}  // namespace data_usage
+
+#endif  // COMPONENTS_DATA_USAGE_ANDROID_TRAFFIC_STATS_AMORTIZER_H_