base/metrics/field_trial.cc

// Copyright (c) 2010 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/metrics/field_trial.h"

#include "base/logging.h"
#include "base/rand_util.h"
#include "base/stringprintf.h"
#include "base/utf_string_conversions.h"

namespace base {

// static
const int FieldTrial::kNotFinalized = -1;

// static
const int FieldTrial::kDefaultGroupNumber = 0;

// static
bool FieldTrial::enable_benchmarking_ = false;

// static
const char FieldTrialList::kPersistentStringSeparator('/');

static const char kHistogramFieldTrialSeparator('_');

//------------------------------------------------------------------------------
// FieldTrial methods and members.

FieldTrial::FieldTrial(const std::string& name,
                       const Probability total_probability,
                       const std::string& default_group_name,
                       const int year,
                       const int month,
                       const int day_of_month)
  : name_(name),
    divisor_(total_probability),
    default_group_name_(default_group_name),
    random_(static_cast<Probability>(divisor_ * base::RandDouble())),
    accumulated_group_probability_(0),
    next_group_number_(kDefaultGroupNumber+1),
    group_(kNotFinalized) {
  DCHECK_GT(total_probability, 0);
  DCHECK(!default_group_name_.empty());
  FieldTrialList::Register(this);

  DCHECK_GT(year, 1970);
  DCHECK_GT(month, 0);
  DCHECK_LT(month, 13);
  DCHECK_GT(day_of_month, 0);
  DCHECK_LT(day_of_month, 32);

  base::Time::Exploded exploded;
  exploded.year = year;
  exploded.month = month;
  exploded.day_of_week = 0;  // Should be unused.
  exploded.day_of_month = day_of_month;
  exploded.hour = 0;
  exploded.minute = 0;
  exploded.second = 0;
  exploded.millisecond = 0;

  base::Time expiration_time = Time::FromLocalExploded(exploded);
  disable_field_trial_ = (GetBuildTime() > expiration_time) ? true : false;
}

int FieldTrial::AppendGroup(const std::string& name,
                            Probability group_probability) {
  DCHECK(group_probability <= divisor_);
  DCHECK_GE(group_probability, 0);

  if (enable_benchmarking_ || disable_field_trial_)
    group_probability = 0;

  accumulated_group_probability_ += group_probability;

  DCHECK(accumulated_group_probability_ <= divisor_);
  if (group_ == kNotFinalized && accumulated_group_probability_ > random_) {
    // This is the group that crossed the random line, so we do the assignment.
    group_ = next_group_number_;
    if (name.empty())
      base::StringAppendF(&group_name_, "%d", group_);
    else
      group_name_ = name;
  }
  return next_group_number_++;
}

int FieldTrial::group() {
  if (group_ == kNotFinalized) {
    accumulated_group_probability_ = divisor_;
    group_ = kDefaultGroupNumber;
    group_name_ = default_group_name_;
  }
  return group_;
}

std::string FieldTrial::group_name() {
  group();  // call group() to make group assignment was done.
  return group_name_;
}

// static
std::string FieldTrial::MakeName(const std::string& name_prefix,
                                 const std::string& trial_name) {
  std::string big_string(name_prefix);
  big_string.append(1, kHistogramFieldTrialSeparator);
  return big_string.append(FieldTrialList::FindFullName(trial_name));
}

// static
void FieldTrial::EnableBenchmarking() {
  DCHECK_EQ(0u, FieldTrialList::GetFieldTrialCount());
  enable_benchmarking_ = true;
}

FieldTrial::~FieldTrial() {}

// static
Time FieldTrial::GetBuildTime() {
  Time integral_build_time;
  const char* kDateTime = __DATE__ " " __TIME__;
  bool result = Time::FromString(ASCIIToWide(kDateTime).c_str(),
                                 &integral_build_time);
  DCHECK(result);
  return integral_build_time;
}

//------------------------------------------------------------------------------
// FieldTrialList methods and members.

// static
FieldTrialList* FieldTrialList::global_ = NULL;

// static
bool FieldTrialList::register_without_global_ = false;

FieldTrialList::FieldTrialList() : application_start_time_(TimeTicks::Now()) {
  DCHECK(!global_);
  DCHECK(!register_without_global_);
  global_ = this;
}

FieldTrialList::~FieldTrialList() {
  AutoLock auto_lock(lock_);
  while (!registered_.empty()) {
    RegistrationList::iterator it = registered_.begin();
    it->second->Release();
    registered_.erase(it->first);
  }
  DCHECK(this == global_);
  global_ = NULL;
}

// static
void FieldTrialList::Register(FieldTrial* trial) {
  if (!global_) {
    register_without_global_ = true;
    return;
  }
  AutoLock auto_lock(global_->lock_);
  DCHECK(!global_->PreLockedFind(trial->name()));
  trial->AddRef();
  global_->registered_[trial->name()] = trial;
}

// static
FieldTrial* FieldTrialList::Find(const std::string& name) {
  if (!global_)
    return NULL;
  AutoLock auto_lock(global_->lock_);
  return global_->PreLockedFind(name);
}

// static
int FieldTrialList::FindValue(const std::string& name) {
  FieldTrial* field_trial = Find(name);
  if (field_trial)
    return field_trial->group();
  return FieldTrial::kNotFinalized;
}

// static
std::string FieldTrialList::FindFullName(const std::string& name) {
  FieldTrial* field_trial = Find(name);
  if (field_trial)
    return field_trial->group_name();
  return "";
}

// static
void FieldTrialList::StatesToString(std::string* output) {
  if (!global_)
    return;
  DCHECK(output->empty());
  AutoLock auto_lock(global_->lock_);
  for (RegistrationList::iterator it = global_->registered_.begin();
       it != global_->registered_.end(); ++it) {
    const std::string name = it->first;
    std::string group_name = it->second->group_name_internal();
    if (group_name.empty())
      // No definitive winner in this trial, use default_group_name as the
      // group_name.
      group_name = it->second->default_group_name();
    DCHECK_EQ(name.find(kPersistentStringSeparator), std::string::npos);
    DCHECK_EQ(group_name.find(kPersistentStringSeparator), std::string::npos);
    output->append(name);
    output->append(1, kPersistentStringSeparator);
    output->append(group_name);
    output->append(1, kPersistentStringSeparator);
  }
}

// static
bool FieldTrialList::CreateTrialsInChildProcess(
    const std::string& parent_trials) {
  DCHECK(global_);
  if (parent_trials.empty() || !global_)
    return true;

  Time::Exploded exploded;
  Time two_years_from_now =
      Time::NowFromSystemTime() + TimeDelta::FromDays(730);
  two_years_from_now.LocalExplode(&exploded);
  const int kTwoYearsFromNow = exploded.year;

  size_t next_item = 0;
  while (next_item < parent_trials.length()) {
    size_t name_end = parent_trials.find(kPersistentStringSeparator, next_item);
    if (name_end == parent_trials.npos || next_item == name_end)
      return false;
    size_t group_name_end = parent_trials.find(kPersistentStringSeparator,
                                               name_end + 1);
    if (group_name_end == parent_trials.npos || name_end + 1 == group_name_end)
      return false;
    std::string name(parent_trials, next_item, name_end - next_item);
    std::string group_name(parent_trials, name_end + 1,
                           group_name_end - name_end - 1);
    next_item = group_name_end + 1;

    FieldTrial *field_trial(FieldTrialList::Find(name));
    if (field_trial) {
      // In single process mode, we may have already created the field trial.
      if ((field_trial->group_name_internal() != group_name) &&
          (field_trial->default_group_name() != group_name))
        return false;
      continue;
    }
    const int kTotalProbability = 100;
    field_trial = new FieldTrial(name, kTotalProbability, group_name,
                                 kTwoYearsFromNow, 1, 1);
    field_trial->AppendGroup(group_name, kTotalProbability);
  }
  return true;
}

// static
size_t FieldTrialList::GetFieldTrialCount() {
  if (!global_)
    return 0;
  AutoLock auto_lock(global_->lock_);
  return global_->registered_.size();
}

FieldTrial* FieldTrialList::PreLockedFind(const std::string& name) {
  RegistrationList::iterator it = registered_.find(name);
  if (registered_.end() == it)
    return NULL;
  return it->second;
}

}  // namespace base