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1 // Copyright (c) 2012 The Chromium Authors. All rights reserved. | 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 | 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 |
12 // manages the state of each such experiment (state == which option was | 12 // manages the state of each such experiment (state == which option was |
13 // pseudo-randomly selected). | 13 // pseudo-randomly selected). |
14 // | 14 // |
15 // States are typically generated randomly, either based on a one time | 15 // States are typically generated randomly, either based on a one time |
16 // randomization (which will yield the same results, in terms of selecting | 16 // randomization (which will yield the same results, in terms of selecting |
17 // the client for a field trial or not, for every run of the program on a | 17 // the client for a field trial or not, for every run of the program on a |
18 // given machine), or by a session randomization (generated each time the | 18 // given machine), or by a session randomization (generated each time the |
19 // application starts up, but held constant during the duration of the | 19 // application starts up, but held constant during the duration of the |
20 // process). | 20 // process). |
21 | 21 |
22 //------------------------------------------------------------------------------ | 22 //------------------------------------------------------------------------------ |
23 // Example: Suppose we have an experiment involving memory, such as determining | 23 // Example: Suppose we have an experiment involving memory, such as determining |
24 // the impact of some pruning algorithm. | 24 // the impact of some pruning algorithm. |
25 // We assume that we already have a histogram of memory usage, such as: | 25 // We assume that we already have a histogram of memory usage, such as: |
26 | 26 |
27 // HISTOGRAM_COUNTS("Memory.RendererTotal", count); | 27 // UMA_HISTOGRAM_COUNTS("Memory.RendererTotal", count); |
28 | 28 |
29 // Somewhere in main thread initialization code, we'd probably define an | 29 // Somewhere in main thread initialization code, we'd probably define an |
30 // instance of a FieldTrial, with code such as: | 30 // instance of a FieldTrial, with code such as: |
31 | 31 |
32 // // FieldTrials are reference counted, and persist automagically until | 32 // // FieldTrials are reference counted, and persist automagically until |
33 // // process teardown, courtesy of their automatic registration in | 33 // // process teardown, courtesy of their automatic registration in |
34 // // FieldTrialList. | 34 // // FieldTrialList. |
35 // // Note: This field trial will run in Chrome instances compiled through | 35 // // Note: This field trial will run in Chrome instances compiled through |
36 // // 8 July, 2015, and after that all instances will be in "StandardMem". | 36 // // 8 July, 2015, and after that all instances will be in "StandardMem". |
37 // scoped_refptr<base::FieldTrial> trial( | 37 // scoped_refptr<base::FieldTrial> trial( |
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478 | 478 |
479 // List of observers to be notified when a group is selected for a FieldTrial. | 479 // List of observers to be notified when a group is selected for a FieldTrial. |
480 scoped_refptr<ObserverListThreadSafe<Observer> > observer_list_; | 480 scoped_refptr<ObserverListThreadSafe<Observer> > observer_list_; |
481 | 481 |
482 DISALLOW_COPY_AND_ASSIGN(FieldTrialList); | 482 DISALLOW_COPY_AND_ASSIGN(FieldTrialList); |
483 }; | 483 }; |
484 | 484 |
485 } // namespace base | 485 } // namespace base |
486 | 486 |
487 #endif // BASE_METRICS_FIELD_TRIAL_H_ | 487 #endif // BASE_METRICS_FIELD_TRIAL_H_ |
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