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1 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved. | 1 // Copyright (c) 2006-2009 The Chromium Authors. All rights reserved. |
2 // Use of this source code is governed by a BSD-style license that can be | 2 // Use of this source code is governed by a BSD-style license that can be |
3 // found in the LICENSE file. | 3 // found in the LICENSE file. |
4 | 4 |
5 // FieldTrial is a class for handling details of statistical experiments | 5 // FieldTrial is a class for handling details of statistical experiments |
6 // performed by actual users in the field (i.e., in a shipped or beta product). | 6 // performed by actual users in the field (i.e., in a shipped or beta product). |
7 // All code is called exclusively on the UI thread currently. | 7 // All code is called exclusively on the UI thread currently. |
8 // | 8 // |
9 // The simplest example is an experiment to see whether one of two options | 9 // The simplest example is an experiment to see whether one of two options |
10 // produces "better" results across our user population. In that scenario, UMA | 10 // produces "better" results across our user population. In that scenario, UMA |
11 // data is uploaded to aggregate the test results, and this FieldTrial class | 11 // data is uploaded to aggregate the test results, and this FieldTrial class |
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43 // SetMemoryModel(LOW); // Sample alternate setting. | 43 // SetMemoryModel(LOW); // Sample alternate setting. |
44 | 44 |
45 // We then modify any histograms we wish to correlate with our experiment to | 45 // We then modify any histograms we wish to correlate with our experiment to |
46 // have slighly different names, depending on what group the trial instance | 46 // have slighly different names, depending on what group the trial instance |
47 // happened (randomly) to be assigned to: | 47 // happened (randomly) to be assigned to: |
48 | 48 |
49 // HISTOGRAM_COUNTS(FieldTrial::MakeName("Memory.RendererTotal", | 49 // HISTOGRAM_COUNTS(FieldTrial::MakeName("Memory.RendererTotal", |
50 // "MemoryExperiment").data(), count); | 50 // "MemoryExperiment").data(), count); |
51 | 51 |
52 // The above code will create 3 distinct histograms, with each run of the | 52 // The above code will create 3 distinct histograms, with each run of the |
53 // application being assigned to of of teh three groups, and for each group, the | 53 // application being assigned to of of the three groups, and for each group, the |
54 // correspondingly named histogram will be populated: | 54 // correspondingly named histogram will be populated: |
55 | 55 |
56 // Memory.RendererTotal // 96% of users still fill this histogram. | 56 // Memory.RendererTotal // 96% of users still fill this histogram. |
57 // Memory.RendererTotal_high_mem // 2% of users will fill this histogram. | 57 // Memory.RendererTotal_high_mem // 2% of users will fill this histogram. |
58 // Memory.RendererTotal_low_mem // 2% of users will fill this histogram. | 58 // Memory.RendererTotal_low_mem // 2% of users will fill this histogram. |
59 | 59 |
60 //------------------------------------------------------------------------------ | 60 //------------------------------------------------------------------------------ |
61 | 61 |
62 #ifndef BASE_FIELD_TRIAL_H_ | 62 #ifndef BASE_FIELD_TRIAL_H_ |
63 #define BASE_FIELD_TRIAL_H_ | 63 #define BASE_FIELD_TRIAL_H_ |
64 | 64 |
65 #include <map> | 65 #include <map> |
66 #include <string> | 66 #include <string> |
67 | 67 |
68 #include "base/lock.h" | 68 #include "base/lock.h" |
69 #include "base/ref_counted.h" | 69 #include "base/ref_counted.h" |
70 #include "base/time.h" | 70 #include "base/time.h" |
71 | 71 |
72 | 72 |
73 class FieldTrial : public base::RefCounted<FieldTrial> { | 73 class FieldTrial : public base::RefCounted<FieldTrial> { |
74 public: | 74 public: |
75 typedef int Probability; // Probability type for being selected in a trial. | 75 typedef int Probability; // Probability type for being selected in a trial. |
76 | 76 |
77 // A return value to indicate that a given instance has not yet had a group | 77 // A return value to indicate that a given instance has not yet had a group |
78 // assignment (and hence is not yet participating in the trial). | 78 // assignment (and hence is not yet participating in the trial). |
79 static const int kNotParticipating; | 79 static const int kNotParticipating; |
80 | 80 |
81 // Provide an easy way to assign all remaining probability to a group. Note | 81 // Provide an easy way to assign all remaining probability to a group. Note |
82 // that this will force an instance to participate, and make it illegal to | 82 // that this will force an instance to participate, and make it illegal to |
83 // attempt to probabalistically add any other groups to the trial. | 83 // attempt to probabalistically add any other groups to the trial. When doing |
| 84 // A/B tests with timings, it is often best to define all groups, so that |
| 85 // histograms will get unique names via the MakeName() methods. |
84 static const Probability kAllRemainingProbability; | 86 static const Probability kAllRemainingProbability; |
85 | 87 |
86 // The name is used to register the instance with the FieldTrialList class, | 88 // The name is used to register the instance with the FieldTrialList class, |
87 // and can be used to find the trial (only one trial can be present for each | 89 // and can be used to find the trial (only one trial can be present for each |
88 // name). | 90 // name). |
89 // Group probabilities that are later supplied must sum to less than or equal | 91 // Group probabilities that are later supplied must sum to less than or equal |
90 // to the total_probability. | 92 // to the total_probability. |
91 FieldTrial(const std::string& name, Probability total_probability); | 93 FieldTrial(const std::string& name, Probability total_probability); |
92 | 94 |
93 // Establish the name and probability of the next group in this trial. | 95 // Establish the name and probability of the next group in this trial. |
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215 | 217 |
216 // Lock for access to registered_. | 218 // Lock for access to registered_. |
217 Lock lock_; | 219 Lock lock_; |
218 RegistrationList registered_; | 220 RegistrationList registered_; |
219 | 221 |
220 DISALLOW_COPY_AND_ASSIGN(FieldTrialList); | 222 DISALLOW_COPY_AND_ASSIGN(FieldTrialList); |
221 }; | 223 }; |
222 | 224 |
223 #endif // BASE_FIELD_TRIAL_H_ | 225 #endif // BASE_FIELD_TRIAL_H_ |
224 | 226 |
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