Win 10 Inactive toast experiment metrics and storage modifications.

chrome/installer/util/experiment_storage.h

+// Copyright 2017 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 CHROME_INSTALLER_UTIL_EXPERIMENT_STORAGE_H_
+#define CHROME_INSTALLER_UTIL_EXPERIMENT_STORAGE_H_
+
+#include <memory>
+
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/strings/string16.h"
+#include "base/win/scoped_handle.h"
+
+namespace base {
+class SingleThreadTaskRunner;
+}
+
+namespace installer {
+
+class Experiment;
+struct ExperimentMetrics;
+
+// Manages the storage of experiment state on the machine.
+//
+// Participation is a per-install property evaluated one time to determine
+// whether or not the install as a whole participates in the study. It is
+// stored in the install's ClientState key.
+//
+// ExperimentMetrics are stored in a per-install experiment_label, while the
+// fine-grained Experiment data are stored in a per-user key in Chrome's
+// ClientState or ClientStateMedium key. For system-level installs, metrics are
+// reported for only a single user on the machine, so only that one user will
+// participate in the experiment.
+//
+// Owing to this "metrics are per-install" property in the face of potentially
+// multiple users running the same install, ExperimentMetrics are considered the
+// source of truth for an install's participation in the experiment. For any
+// given state expressed in the experiment_label holding these metrics, there
+// should be matching Experiment data for precisely one user.
+//
+// As state is written across multiple locations in the registry, a global
+// mutex is used for all reads and writes to ensure consistent state.
+class ExperimentStorage {
+ public:
+  enum class Participation {
+    // No participation state was found for the install.
+    kNotEvaluated,
+
+    // The client is not participating in the study.
+    kNotParticipating,
+
+    // The client is participating in the study.
+    kIsParticipating,
+  };
+
+  // Grants the holder exclusive access to the data in the registry. Consumers
+  // are expected to not hold an instance across any blocking operations.
+  class Lock {
+   public:
+    ~Lock();
+
+    // Reads the participation state for the install. Returns false in case of
+    // error.
+    bool ReadParticipation(Participation* participation);
+
+    // Writes the participation state for the install. Returns false if the
+    // write failed.
+    bool WriteParticipation(Participation participation);
+
+    // Loads the experiment metrics and data from the registry. Returns false if
+    // the state in the registry corresponds to a different user or could not be
+    // read.
+    bool LoadExperiment(Experiment* experiment);
+
+    // Stores the experiment metrics and data in |experiment| into the registry.
+    bool StoreExperiment(const Experiment& experiment);
+
+    // Loads per-install experiment metrics into |metrics|. Returns true if a
+    // value was read or if none was found, in which case |metrics| is set to
+    // the uninitialized state. Returns false in case of any error reading or
+    // parsing the metrics.
+    bool LoadMetrics(ExperimentMetrics* metrics);
+
+    // Stores |metrics| in the per-install experiment_label.
+    bool StoreMetrics(const ExperimentMetrics& metrics);
+
+   private:
+    friend ExperimentStorage;
+
+    explicit Lock(ExperimentStorage* storage);
+
+    ExperimentStorage* storage_;
+
+    DISALLOW_COPY_AND_ASSIGN(Lock);
+  };
+
+  ExperimentStorage();
+  ~ExperimentStorage();
+
+  // Returns exclusive access to the experiment storage.
+  std::unique_ptr<Lock> AcquireLock();
+
+ private:
+  // Reads |len| bits ending at |low_bit| of a 64 bit unsigned int into an int.
+  static int ReadUint64Bits(uint64_t source, int low_bit, int len);
+
+  // Sets the last |len| bits of |value| into |source| at bit position
+  // ending at low_bit.
+  static void ExperimentStorage::SetUint64Bits(int value,

[grt (UTC plus 2), 2017/05/31 12:24:10]

nit: omit "ExperimentStorage::"

[nikunjb, 2017/06/02 05:11:23]

Done.

+                                               int len,
+                                               int low_bit,
+                                               uint64_t* source);
+
+  // Decodes |encoded_metrics| into |metrics|, return true on success. Returns
+  // false if the encoding is malformed.
+  static bool DecodeMetrics(base::StringPiece16 encoded_metrics,
+                            ExperimentMetrics* metrics);
+
+  // Returns the encoded form of |metrics|.
+  static base::string16 EncodeMetrics(const ExperimentMetrics& metrics);
+
+  // Returns a partial encoding of |metrics| into a client_id value.
+  static base::string16 EncodeClientId(const ExperimentMetrics& metrics);
+
+  // Loads the per-install experiment metrics into |metrics|. Returns true if a
+  // value was read or if none was found, in which case |metrics| is set to the
+  // uninitialized state. Returns false in case of any error reading or parsing
+  // the metrics.
+  bool LoadMetricsUnsafe(ExperimentMetrics* metrics);
+
+  // StoreMetrics without acquiring the mutex.
+  bool StoreMetricsUnsafe(const ExperimentMetrics& metrics);
+
+  // Loads the experiment state for the current user's Retention key into
+  // |experiment|. Returns true if all values are read. Returns false otherwise,
+  // in which case |experiment| is left in an undefined state.
+  bool LoadStateUnsafe(Experiment* experiment);
+
+  // Stores |experiment| in the current user's Retention key.
+  bool StoreStateUnsafe(const Experiment& experiment);
+
+  // Returns the instance's task runner for COM usage. The runner is created on

[grt (UTC plus 2), 2017/05/31 12:24:09]

oops -- please delete this and the task_runner_ member (and clean up the forward
decls/includes). they are leftover from a failed attempt to update the "client"
value.

[nikunjb, 2017/06/02 05:11:23]

Done.

+  // demand.
+  scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunner();
+
+  // A global mutex with a distinct name for the current installation.
+  base::win::ScopedHandle mutex_;
+
+  FRIEND_TEST_ALL_PREFIXES(ExperimentStorageTest, TestEncodeDecodeMetrics);

[grt (UTC plus 2), 2017/05/31 12:24:09]

nit: move these up to the top of the private: section

[nikunjb, 2017/06/02 05:11:23]

Done.

+  FRIEND_TEST_ALL_PREFIXES(ExperimentStorageTest, TestLoadStoreMetrics);
+  FRIEND_TEST_ALL_PREFIXES(ExperimentStorageTest, TestLoadStoreExperiment);
+
+  // A task runner initialized into a COM STA for use by the client id updater.
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+
+  DISALLOW_COPY_AND_ASSIGN(ExperimentStorage);
+};
+
+}  // namespace installer
+
+#endif  // CHROME_INSTALLER_UTIL_EXPERIMENT_STORAGE_H_