xref: /aosp_15_r20/external/webrtc/api/field_trials.cc (revision d9f758449e529ab9291ac668be2861e7a55c2422)
1 /*
2  *  Copyright (c) 2020 The WebRTC project authors. All Rights Reserved.
3  *
4  *  Use of this source code is governed by a BSD-style license
5  *  that can be found in the LICENSE file in the root of the source
6  *  tree. An additional intellectual property rights grant can be found
7  *  in the file PATENTS.  All contributing project authors may
8  *  be found in the AUTHORS file in the root of the source tree.
9  */
10 
11 #include "api/field_trials.h"
12 
13 #include <atomic>
14 
15 #include "rtc_base/checks.h"
16 #include "system_wrappers/include/field_trial.h"
17 
18 namespace {
19 
20 // This part is copied from system_wrappers/field_trial.cc.
InsertIntoMap(const std::string & s)21 webrtc::flat_map<std::string, std::string> InsertIntoMap(const std::string& s) {
22   std::string::size_type field_start = 0;
23   webrtc::flat_map<std::string, std::string> key_value_map;
24   while (field_start < s.size()) {
25     std::string::size_type separator_pos = s.find('/', field_start);
26     RTC_CHECK_NE(separator_pos, std::string::npos)
27         << "Missing separator '/' after field trial key.";
28     RTC_CHECK_GT(separator_pos, field_start)
29         << "Field trial key cannot be empty.";
30     std::string key = s.substr(field_start, separator_pos - field_start);
31     field_start = separator_pos + 1;
32 
33     RTC_CHECK_LT(field_start, s.size())
34         << "Missing value after field trial key. String ended.";
35     separator_pos = s.find('/', field_start);
36     RTC_CHECK_NE(separator_pos, std::string::npos)
37         << "Missing terminating '/' in field trial string.";
38     RTC_CHECK_GT(separator_pos, field_start)
39         << "Field trial value cannot be empty.";
40     std::string value = s.substr(field_start, separator_pos - field_start);
41     field_start = separator_pos + 1;
42 
43     // If a key is specified multiple times, only the value linked to the first
44     // key is stored. note: This will crash in debug build when calling
45     // InitFieldTrialsFromString().
46     key_value_map.emplace(key, value);
47   }
48   // This check is technically redundant due to earlier checks.
49   // We nevertheless keep the check to make it clear that the entire
50   // string has been processed, and without indexing past the end.
51   RTC_CHECK_EQ(field_start, s.size());
52 
53   return key_value_map;
54 }
55 
56 // Makes sure that only one instance is created, since the usage
57 // of global string makes behaviour unpredicatable otherwise.
58 // TODO(bugs.webrtc.org/10335): Remove once global string is gone.
59 std::atomic<bool> instance_created_{false};
60 
61 }  // namespace
62 
63 namespace webrtc {
64 
FieldTrials(const std::string & s)65 FieldTrials::FieldTrials(const std::string& s)
66     : uses_global_(true),
67       field_trial_string_(s),
68       previous_field_trial_string_(webrtc::field_trial::GetFieldTrialString()),
69       key_value_map_(InsertIntoMap(s)) {
70   // TODO(bugs.webrtc.org/10335): Remove the global string!
71   field_trial::InitFieldTrialsFromString(field_trial_string_.c_str());
72   RTC_CHECK(!instance_created_.exchange(true))
73       << "Only one instance may be instanciated at any given time!";
74 }
75 
CreateNoGlobal(const std::string & s)76 std::unique_ptr<FieldTrials> FieldTrials::CreateNoGlobal(const std::string& s) {
77   return std::unique_ptr<FieldTrials>(new FieldTrials(s, true));
78 }
79 
FieldTrials(const std::string & s,bool)80 FieldTrials::FieldTrials(const std::string& s, bool)
81     : uses_global_(false),
82       previous_field_trial_string_(nullptr),
83       key_value_map_(InsertIntoMap(s)) {}
84 
~FieldTrials()85 FieldTrials::~FieldTrials() {
86   // TODO(bugs.webrtc.org/10335): Remove the global string!
87   if (uses_global_) {
88     field_trial::InitFieldTrialsFromString(previous_field_trial_string_);
89     RTC_CHECK(instance_created_.exchange(false));
90   }
91 }
92 
GetValue(absl::string_view key) const93 std::string FieldTrials::GetValue(absl::string_view key) const {
94   auto it = key_value_map_.find(std::string(key));
95   if (it != key_value_map_.end())
96     return it->second;
97 
98   // Check the global string so that programs using
99   // a mix between FieldTrials and the global string continue to work
100   // TODO(bugs.webrtc.org/10335): Remove the global string!
101   if (uses_global_) {
102     return field_trial::FindFullName(std::string(key));
103   }
104   return "";
105 }
106 
107 }  // namespace webrtc
108