chrome/browser/metrics/field_trial_synchronizer.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef CHROME_BROWSER_METRICS_FIELD_TRIAL_SYNCHRONIZER_H_
   6 #define CHROME_BROWSER_METRICS_FIELD_TRIAL_SYNCHRONIZER_H_
   7
   8 #include <string>
   9 #include <vector>
  10
  11 #include "base/basictypes.h"
  12 #include "base/memory/ref_counted.h"
  13 #include "base/metrics/field_trial.h"
  14
  15 // This class is used by the browser process to communicate FieldTrial setting
  16 // (field trial name and group) to any previously started renderers.
  17 //
  18 // This class registers itself as an observer of FieldTrialList. FieldTrialList
  19 // notifies this class by calling it's OnFieldTrialGroupFinalized method when a
  20 // group is selected (finalized) for a FieldTrial and OnFieldTrialGroupFinalized
  21 // method sends the FieldTrial's name and the group to all renderer processes.
  22 // Each renderer process creates the FieldTrial, and by using a 100% probability
  23 // for the FieldTrial, forces the FieldTrial to have the same group string.
  24
  25 class FieldTrialSynchronizer
  26     : public base::RefCountedThreadSafe<FieldTrialSynchronizer>,
  27       public base::FieldTrialList::Observer {
  28  public:
  29   // Construction also sets up the global singleton instance.  This instance is
  30   // used to communicate between the UI and other threads, and is destroyed only
  31   // as the main thread (browser_main) terminates, which means all other threads
  32   // have completed, and will not need this instance any further. It adds itself
  33   // as an observer of FieldTrialList so that it gets notified whenever a group
  34   // is finalized in the browser process.
  35   FieldTrialSynchronizer();
  36
  37   // Notify all renderer processes about the |group_name| that is finalized for
  38   // the given field trail (|field_trial_name|). This is called on UI thread.
  39   void NotifyAllRenderers(const std::string& field_trial_name,
  40                           const std::string& group_name);
  41
  42   // FieldTrialList::Observer methods:
  43
  44   // This method is called by the FieldTrialList singleton when a trial's group
  45   // is finalized. This method contacts all renderers (by calling
  46   // NotifyAllRenderers) to create a FieldTrial that carries the randomly
  47   // selected state from the browser process into all the renderer processes.
  48   void OnFieldTrialGroupFinalized(const std::string& name,
  49                                   const std::string& group_name) override;
  50
  51  private:
  52   friend class base::RefCountedThreadSafe<FieldTrialSynchronizer>;
  53   ~FieldTrialSynchronizer() override;
  54
  55   DISALLOW_COPY_AND_ASSIGN(FieldTrialSynchronizer);
  56 };
  57
  58 #endif  // CHROME_BROWSER_METRICS_FIELD_TRIAL_SYNCHRONIZER_H_