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1 // Copyright 2016 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 BASE_METRICS_FIELD_TRIAL_PARAM_ASSOCIATOR_H_
6 #define BASE_METRICS_FIELD_TRIAL_PARAM_ASSOCIATOR_H_
7 
8 #include <map>
9 #include <string>
10 #include <utility>
11 
12 #include "base/base_export.h"
13 #include "base/memory/singleton.h"
14 #include "base/metrics/field_trial.h"
15 #include "base/synchronization/lock.h"
16 
17 namespace base {
18 
19 // Keeps track of the parameters of all field trials and ensures access to them
20 // is thread-safe.
21 class BASE_EXPORT FieldTrialParamAssociator {
22  public:
23   FieldTrialParamAssociator();
24   ~FieldTrialParamAssociator();
25 
26   // Key-value mapping type for field trial parameters.
27   typedef std::map<std::string, std::string> FieldTrialParams;
28 
29   // Retrieve the singleton.
30   static FieldTrialParamAssociator* GetInstance();
31 
32   // Sets parameters for the given field trial name and group.
33   bool AssociateFieldTrialParams(const std::string& trial_name,
34                                  const std::string& group_name,
35                                  const FieldTrialParams& params);
36 
37   // Gets the parameters for a field trial and its chosen group. If not found in
38   // field_trial_params_, then tries to looks it up in shared memory.
39   bool GetFieldTrialParams(const std::string& trial_name,
40                            FieldTrialParams* params);
41 
42   // Gets the parameters for a field trial and its chosen group. Does not
43   // fallback to looking it up in shared memory. This should only be used if you
44   // know for sure the params are in the mapping, like if you're in the browser
45   // process, and even then you should probably just use GetFieldTrialParams().
46   bool GetFieldTrialParamsWithoutFallback(const std::string& trial_name,
47                                           const std::string& group_name,
48                                           FieldTrialParams* params);
49 
50   // Clears the internal field_trial_params_ mapping, plus removes all params in
51   // shared memory.
52   void ClearAllParamsForTesting();
53 
54   // Clears a single field trial param.
55   // Note: this does NOT remove the param in shared memory.
56   void ClearParamsForTesting(const std::string& trial_name,
57                              const std::string& group_name);
58 
59   // Clears the internal field_trial_params_ mapping.
60   void ClearAllCachedParamsForTesting();
61 
62  private:
63   friend struct DefaultSingletonTraits<FieldTrialParamAssociator>;
64 
65   // (field_trial_name, field_trial_group)
66   typedef std::pair<std::string, std::string> FieldTrialKey;
67 
68   Lock lock_;
69   std::map<FieldTrialKey, FieldTrialParams> field_trial_params_;
70 
71   DISALLOW_COPY_AND_ASSIGN(FieldTrialParamAssociator);
72 };
73 
74 }  // namespace base
75 
76 #endif  // BASE_METRICS_FIELD_TRIAL_PARAM_ASSOCIATOR_H_
77