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1 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved. | 1 // Copyright (c) 2006-2008 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 a test to see whether one of two options produces | 9 // The simplest example is an experiment to see whether one of two options |
10 // "better" results across our user population. In that scenario, UMA data | 10 // produces "better" results across our user population. In that scenario, UMA |
11 // is uploaded to show the test results, and this class manages the state of | 11 // data is uploaded to aggregate the test results, and this FieldTrial class |
12 // each such test (state == which option was pseudo-randomly selected). | 12 // manages the state of each such experiment (state == which option was |
| 13 // pseudo-randomly selected). |
| 14 // |
13 // States are typically generated randomly, either based on a one time | 15 // States are typically generated randomly, either based on a one time |
14 // randomization (reused during each run of the program), or by a startup | 16 // randomization (generated randomly once, and then persitently reused in the |
15 // randomization (keeping that tests state constant across a run), or by | 17 // client during each future run of the program), or by a startup randomization |
16 // continuous randomization across a run. | 18 // (generated each time the application starts up, but held constant during the |
17 // Only startup randomization is implemented (thus far). | 19 // duration of the process), or by continuous randomization across a run (where |
| 20 // the state can be recalculated again and again, many times during a process). |
| 21 // Only startup randomization is implemented thus far. |
| 22 |
| 23 //------------------------------------------------------------------------------ |
| 24 // Example: Suppose we have an experiment involving memory, such as determining |
| 25 // the impact of memory model command line flags actual memory use. |
| 26 // We assume that we already have a histogram of memory usage, such as: |
| 27 |
| 28 // HISTOGRAM_COUNTS("Memory.RendererTotal", count); |
| 29 |
| 30 // Somewhere in main thread initialization code, we'd probably define an |
| 31 // instance of a FieldTrial, with code such as: |
| 32 |
| 33 // // Note, FieldTrials are reference counted, and persist automagically until |
| 34 // // process teardown, courtesy of their automatic registration in |
| 35 // // FieldTrialList. |
| 36 // trial = new FieldTrial("MemoryExperiment", 1000); |
| 37 // group1 = trial->AppendGroup("_high_mem", 20); // 2% this _high_mem group. |
| 38 // group2 = trial->AppendGroup("_low_mem", 20); // 2% this _low_mem group. |
| 39 // // Take action depending of which group we randomly land in. |
| 40 // switch (trial->group()) { |
| 41 // case group1: |
| 42 // ... do something |
| 43 // break; |
| 44 // case group2: |
| 45 // .... |
| 46 // break; |
| 47 // default: |
| 48 // ... |
| 49 // } |
| 50 |
| 51 // We then modify any histograms we wish to correlate with our experiment to |
| 52 // have slighly different names, depending on what group the trial instance |
| 53 // happened (randomly) to be assigned to: |
| 54 |
| 55 // HISTOGRAM_COUNTS(FieldTrial::MakeName("Memory.RendererTotal", |
| 56 // "MemoryExperiment"), count); |
| 57 |
| 58 // The above code will create 3 distinct histograms, with each run of the |
| 59 // application being assigned to of of teh three groups, and for each group, the |
| 60 // correspondingly named histogram will be populated: |
| 61 |
| 62 // Memory.RendererTotal // 96% of users still fill this histogram. |
| 63 // Memory.RendererTotal_high_mem // 2% of users will fill this histogram. |
| 64 // Memory.RendererTotal_low_mem // 2% of users will fill this histogram. |
| 65 |
| 66 //------------------------------------------------------------------------------ |
18 | 67 |
19 #ifndef BASE_FIELD_TRIAL_H_ | 68 #ifndef BASE_FIELD_TRIAL_H_ |
20 #define BASE_FIELD_TRIAL_H_ | 69 #define BASE_FIELD_TRIAL_H_ |
21 | 70 |
22 #include <map> | 71 #include <map> |
23 #include <string> | 72 #include <string> |
24 | 73 |
25 #include "base/non_thread_safe.h" | 74 #include "base/non_thread_safe.h" |
26 #include "base/ref_counted.h" | 75 #include "base/ref_counted.h" |
27 #include "base/time.h" | 76 #include "base/time.h" |
28 | 77 |
| 78 |
29 class FieldTrial : public base::RefCounted<FieldTrial> { | 79 class FieldTrial : public base::RefCounted<FieldTrial> { |
30 public: | 80 public: |
31 // Constructor for a 2-state (boolean) trial. | 81 static const int kNotParticipating = -1; |
| 82 |
| 83 typedef int Probability; // Use scaled up probability. |
| 84 |
32 // The name is used to register the instance with the FieldTrialList class, | 85 // The name is used to register the instance with the FieldTrialList class, |
33 // and can be used to find the trial (only one trial can be present for each | 86 // and can be used to find the trial (only one trial can be present for each |
34 // name) using the Find() method. | 87 // name). |
35 // The probability is a number in the range [0, 1], and is the likliehood that | 88 // Group probabilities that are later supplied must sum to less than or equal |
36 // the assigned boolean value will be true. | 89 // to the total_probability. |
37 FieldTrial(const std::wstring& name, double probability); | 90 FieldTrial(const std::string& name, Probability total_probability); |
38 | 91 |
39 // Return the selected boolean value. | 92 // Establish the name and probability of the next group in this trial. |
40 bool boolean_value() const { return boolean_value_; } | 93 // Sometimes, based on construction randomization, this call may causes the |
41 std::wstring name() const { return name_; } | 94 // provided group to be *THE* group selected for use in this instance. |
| 95 int AppendGroup(const std::string& name, Probability group_probability); |
| 96 |
| 97 // Return the name of the FieldTrial (excluding the group name). |
| 98 std::string name() const { return name_; } |
| 99 |
| 100 // Return the randomly selected group number that was assigned. |
| 101 // Return kNotParticipating if the instance is not participating in the |
| 102 // experiment. |
| 103 int group() const { return group_; } |
| 104 |
| 105 // If the field trial is not in an experiment, this returns the empty string. |
| 106 // if the group's name is empty, a name of "_" concatenated with the group |
| 107 // number is used as the group name. |
| 108 std::string group_name() const { return group_name_; } |
| 109 |
| 110 // Helper function for the most common use: as an argument to specifiy the |
| 111 // name of a HISTOGRAM. Use the original histogram name as the name_prefix. |
| 112 static std::string MakeName(const std::string& name_prefix, |
| 113 const std::string& trial_name); |
42 | 114 |
43 private: | 115 private: |
44 const std::wstring name_; | 116 // The name of the field trial, as can be found via the FieldTrialList. |
45 bool boolean_value_; | 117 // This is empty of the trial is not in the experiment. |
| 118 const std::string name_; |
| 119 |
| 120 // The maximu sum of all probabilities supplied, which corresponds to 100%. |
| 121 // This is the scaling factor used to adjust supplied probabilities. |
| 122 Probability divisor_; |
| 123 |
| 124 // The randomly selected probability that is used to select a group (or have |
| 125 // the instance not participate). It is the product of divisor_ and a random |
| 126 // number between [0, 1). |
| 127 Probability random_; |
| 128 |
| 129 // Sum of the probabilities of all appended groups. |
| 130 Probability accumulated_group_probability_; |
| 131 |
| 132 int next_group_number_; |
| 133 |
| 134 // The pseudo-randomly assigned group number. |
| 135 // This is kNotParticipating if no group has been assigned. |
| 136 int group_; |
| 137 |
| 138 // A textual name for the randomly selected group, including the Trial name. |
| 139 // If this Trial is not a member of an group, this string is empty. |
| 140 std::string group_name_; |
46 | 141 |
47 DISALLOW_COPY_AND_ASSIGN(FieldTrial); | 142 DISALLOW_COPY_AND_ASSIGN(FieldTrial); |
48 }; | 143 }; |
49 | 144 |
| 145 //------------------------------------------------------------------------------ |
50 // Class with a list of all active field trials. A trial is active if it has | 146 // Class with a list of all active field trials. A trial is active if it has |
51 // been registered, which includes evaluating its state based on its probaility. | 147 // been registered, which includes evaluating its state based on its probaility. |
52 // Only one instance of this class exists. | 148 // Only one instance of this class exists. |
53 class FieldTrialList : NonThreadSafe { | 149 class FieldTrialList : NonThreadSafe { |
54 public: | 150 public: |
55 // This singleton holds the global list of registered FieldTrials. | 151 // This singleton holds the global list of registered FieldTrials. |
56 FieldTrialList(); | 152 FieldTrialList(); |
57 // Destructor Release()'s references to all registered FieldTrial instances. | 153 // Destructor Release()'s references to all registered FieldTrial instances. |
58 ~FieldTrialList(); | 154 ~FieldTrialList(); |
59 | 155 |
60 // Register() stores a pointer to the given trial in a global map. | 156 // Register() stores a pointer to the given trial in a global map. |
61 // This method also AddRef's the indicated trial. | 157 // This method also AddRef's the indicated trial. |
62 static void Register(FieldTrial* trial); | 158 static void Register(FieldTrial* trial); |
63 | 159 |
64 // The Find() method can be used to test to see if a named Trial was already | 160 // The Find() method can be used to test to see if a named Trial was already |
65 // registered, or to retrieve a pointer to it from the global map. | 161 // registered, or to retrieve a pointer to it from the global map. |
66 static FieldTrial* Find(const std::wstring& name); | 162 static FieldTrial* Find(const std::string& name); |
| 163 |
| 164 static int FindValue(const std::string& name); |
| 165 |
| 166 static std::string FindFullName(const std::string& name); |
67 | 167 |
68 // The time of construction of the global map is recorded in a static variable | 168 // The time of construction of the global map is recorded in a static variable |
69 // and is commonly used by experiments to identify the time since the start | 169 // and is commonly used by experiments to identify the time since the start |
70 // of the application. In some experiments it may be useful to discount | 170 // of the application. In some experiments it may be useful to discount |
71 // data that is gathered before the application has reach sufficient | 171 // data that is gathered before the application has reached sufficient |
72 // stability (example: most DLL have loaded, etc.) | 172 // stability (example: most DLL have loaded, etc.) |
73 static base::Time application_start_time() { | 173 static base::Time application_start_time() { |
74 if (global_) | 174 if (global_) |
75 return global_->application_start_time_; | 175 return global_->application_start_time_; |
76 // For testing purposes only, or when we don't yet have a start time. | 176 // For testing purposes only, or when we don't yet have a start time. |
77 return base::Time::Now(); | 177 return base::Time::Now(); |
78 } | 178 } |
79 | 179 |
80 private: | 180 private: |
81 typedef std::map<std::wstring, FieldTrial*> RegistrationList; | 181 typedef std::map<std::string, FieldTrial*> RegistrationList; |
82 | 182 |
83 static FieldTrialList* global_; // The singleton of this class. | 183 static FieldTrialList* global_; // The singleton of this class. |
84 | 184 |
85 base::Time application_start_time_; | 185 base::Time application_start_time_; |
86 RegistrationList registered_; | 186 RegistrationList registered_; |
87 | 187 |
88 DISALLOW_COPY_AND_ASSIGN(FieldTrialList); | 188 DISALLOW_COPY_AND_ASSIGN(FieldTrialList); |
89 }; | 189 }; |
90 | 190 |
91 #endif // BASE_FIELD_TRIAL_H_ | 191 #endif // BASE_FIELD_TRIAL_H_ |
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