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 virtual void OnFieldTrialGroupFinalized( 49 const std::string& name, 50 const std::string& group_name) OVERRIDE; 51 52 private: 53 friend class base::RefCountedThreadSafe<FieldTrialSynchronizer>; 54 virtual ~FieldTrialSynchronizer(); 55 56 DISALLOW_COPY_AND_ASSIGN(FieldTrialSynchronizer); 57 }; 58 59 #endif // CHROME_BROWSER_METRICS_FIELD_TRIAL_SYNCHRONIZER_H_ 60
