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// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/feature_list.h"
#include <utility>
#include <vector>
#include "base/logging.h"
#include "base/metrics/field_trial.h"
#include "base/strings/string_split.h"
namespace base {
namespace {
// Pointer to the FeatureList instance singleton that was set via
// FeatureList::SetInstance(). Does not use base/memory/singleton.h in order to
// have more control over initialization timing. Leaky.
FeatureList* g_instance = nullptr;
} // namespace
FeatureList::FeatureList() : initialized_(false) {}
FeatureList::~FeatureList() {}
void FeatureList::InitializeFromCommandLine(
const std::string& enable_features,
const std::string& disable_features) {
DCHECK(!initialized_);
// Process disabled features first, so that disabled ones take precedence over
// enabled ones (since RegisterOverride() uses insert()).
for (const auto& feature_name : SplitFeatureListString(disable_features)) {
RegisterOverride(feature_name, OVERRIDE_DISABLE_FEATURE, nullptr);
}
for (const auto& feature_name : SplitFeatureListString(enable_features)) {
RegisterOverride(feature_name, OVERRIDE_ENABLE_FEATURE, nullptr);
}
}
bool FeatureList::IsFeatureOverriddenFromCommandLine(
const std::string& feature_name,
OverrideState state) const {
auto it = overrides_.find(feature_name);
return it != overrides_.end() && it->second.overridden_state == state &&
!it->second.overridden_by_field_trial;
}
void FeatureList::RegisterFieldTrialOverride(const std::string& feature_name,
OverrideState override_state,
FieldTrial* field_trial) {
DCHECK(field_trial);
DCHECK(!ContainsKey(overrides_, feature_name) ||
!overrides_.find(feature_name)->second.field_trial)
<< "Feature " << feature_name
<< " has conflicting field trial overrides: "
<< overrides_.find(feature_name)->second.field_trial->trial_name()
<< " / " << field_trial->trial_name();
RegisterOverride(feature_name, override_state, field_trial);
}
void FeatureList::AssociateReportingFieldTrial(
const std::string& feature_name,
OverrideState for_overridden_state,
FieldTrial* field_trial) {
DCHECK(
IsFeatureOverriddenFromCommandLine(feature_name, for_overridden_state));
// Only one associated field trial is supported per feature. This is generally
// enforced server-side.
OverrideEntry* entry = &overrides_.find(feature_name)->second;
if (entry->field_trial) {
NOTREACHED() << "Feature " << feature_name
<< " already has trial: " << entry->field_trial->trial_name()
<< ", associating trial: " << field_trial->trial_name();
return;
}
entry->field_trial = field_trial;
}
// static
bool FeatureList::IsEnabled(const Feature& feature) {
return GetInstance()->IsFeatureEnabled(feature);
}
// static
std::vector<std::string> FeatureList::SplitFeatureListString(
const std::string& input) {
return SplitString(input, ",", TRIM_WHITESPACE, SPLIT_WANT_NONEMPTY);
}
// static
FeatureList* FeatureList::GetInstance() {
return g_instance;
}
// static
void FeatureList::SetInstance(scoped_ptr<FeatureList> instance) {
DCHECK(!g_instance);
instance->FinalizeInitialization();
// Note: Intentional leak of global singleton.
g_instance = instance.release();
}
// static
void FeatureList::ClearInstanceForTesting() {
delete g_instance;
g_instance = nullptr;
}
void FeatureList::FinalizeInitialization() {
DCHECK(!initialized_);
initialized_ = true;
}
bool FeatureList::IsFeatureEnabled(const Feature& feature) {
DCHECK(initialized_);
DCHECK(CheckFeatureIdentity(feature)) << feature.name;
auto it = overrides_.find(feature.name);
if (it != overrides_.end()) {
const OverrideEntry& entry = it->second;
// Activate the corresponding field trial, if necessary.
if (entry.field_trial)
entry.field_trial->group();
// TODO(asvitkine) Expand this section as more support is added.
return entry.overridden_state == OVERRIDE_ENABLE_FEATURE;
}
// Otherwise, return the default state.
return feature.default_state == FEATURE_ENABLED_BY_DEFAULT;
}
void FeatureList::RegisterOverride(const std::string& feature_name,
OverrideState overridden_state,
FieldTrial* field_trial) {
DCHECK(!initialized_);
// Note: The semantics of insert() is that it does not overwrite the entry if
// one already exists for the key. Thus, only the first override for a given
// feature name takes effect.
overrides_.insert(std::make_pair(
feature_name, OverrideEntry(overridden_state, field_trial)));
}
bool FeatureList::CheckFeatureIdentity(const Feature& feature) {
AutoLock auto_lock(feature_identity_tracker_lock_);
auto it = feature_identity_tracker_.find(feature.name);
if (it == feature_identity_tracker_.end()) {
// If it's not tracked yet, register it.
feature_identity_tracker_[feature.name] = &feature;
return true;
}
// Compare address of |feature| to the existing tracked entry.
return it->second == &feature;
}
FeatureList::OverrideEntry::OverrideEntry(OverrideState overridden_state,
FieldTrial* field_trial)
: overridden_state(overridden_state),
field_trial(field_trial),
overridden_by_field_trial(field_trial != nullptr) {}
} // namespace base
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