chrome/browser/metrics/field_trial_synchronizer.cc

// Copyright (c) 2012 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 "chrome/browser/metrics/field_trial_synchronizer.h"

#include "base/bind.h"
#include "base/logging.h"
#include "base/task/post_task.h"
#include "base/threading/thread.h"
#include "chrome/common/renderer_configuration.mojom.h"
#include "components/metrics/persistent_system_profile.h"
#include "content/public/browser/browser_task_traits.h"
#include "content/public/browser/browser_thread.h"
#include "content/public/browser/render_process_host.h"
#include "mojo/public/cpp/bindings/associated_remote.h"

using content::BrowserThread;

namespace {

void AddFieldTrialToPersistentSystemProfile(const std::string& field_trial_name,
                                            const std::string& group_name) {
  // Note this in the persistent profile as it will take a while for a new
  // "complete" profile to be generated.
  metrics::GlobalPersistentSystemProfile::GetInstance()->AddFieldTrial(
      field_trial_name, group_name);
}

}  // namespace

FieldTrialSynchronizer::FieldTrialSynchronizer() {
  bool success = base::FieldTrialList::AddObserver(this);
  // Ensure the observer was actually registered.
  DCHECK(success);
}

void FieldTrialSynchronizer::NotifyAllRenderers(
    const std::string& field_trial_name,
    const std::string& group_name) {
  // To iterate over RenderProcessHosts, or to send messages to the hosts, we
  // need to be on the UI thread.
  DCHECK_CURRENTLY_ON(BrowserThread::UI);

  AddFieldTrialToPersistentSystemProfile(field_trial_name, group_name);

  for (content::RenderProcessHost::iterator it(
          content::RenderProcessHost::AllHostsIterator());
       !it.IsAtEnd(); it.Advance()) {
    auto* host = it.GetCurrentValue();
    IPC::ChannelProxy* channel = host->GetChannel();
    // channel might be null in tests.
    if (host->IsInitializedAndNotDead() && channel) {
      mojo::AssociatedRemote<chrome::mojom::RendererConfiguration>
          renderer_configuration;
      channel->GetRemoteAssociatedInterface(&renderer_configuration);
      renderer_configuration->SetFieldTrialGroup(field_trial_name, group_name);
    }
  }
}

void FieldTrialSynchronizer::OnFieldTrialGroupFinalized(
    const std::string& field_trial_name,
    const std::string& group_name) {
  // The FieldTrialSynchronizer may have been created before any BrowserThread
  // is created, so we don't need to synchronize with child processes in which
  // case there are no child processes to notify yet. But we want to update the
  // persistent system profile, thus the histogram data recorded in the reduced
  // mode will be tagged to its corresponding field trial experiment.
  if (!content::BrowserThread::IsThreadInitialized(BrowserThread::UI)) {
    AddFieldTrialToPersistentSystemProfile(field_trial_name, group_name);
    return;
  }

  base::PostTask(FROM_HERE, {BrowserThread::UI},
                 base::BindOnce(&FieldTrialSynchronizer::NotifyAllRenderers,
                                this, field_trial_name, group_name));
}

FieldTrialSynchronizer::~FieldTrialSynchronizer() {
  base::FieldTrialList::RemoveObserver(this);
}