base/metrics/field_trial.cc

   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
   3 // found in the LICENSE file.
   4
   5 #include "base/metrics/field_trial.h"
   6
   7 #include <algorithm>
   8
   9 #include "base/build_time.h"
  10 #include "base/logging.h"
  11 #include "base/rand_util.h"
  12 #include "base/sha1.h"
  13 #include "base/strings/string_util.h"
  14 #include "base/strings/stringprintf.h"
  15 #include "base/strings/utf_string_conversions.h"
  16 #include "base/sys_byteorder.h"
  17
  18 namespace base {
  19
  20 namespace {
  21
  22 // Created a time value based on |year|, |month| and |day_of_month| parameters.
  23 Time CreateTimeFromParams(int year, int month, int day_of_month) {
  24   DCHECK_GT(year, 1970);
  25   DCHECK_GT(month, 0);
  26   DCHECK_LT(month, 13);
  27   DCHECK_GT(day_of_month, 0);
  28   DCHECK_LT(day_of_month, 32);
  29
  30   Time::Exploded exploded;
  31   exploded.year = year;
  32   exploded.month = month;
  33   exploded.day_of_week = 0;  // Should be unused.
  34   exploded.day_of_month = day_of_month;
  35   exploded.hour = 0;
  36   exploded.minute = 0;
  37   exploded.second = 0;
  38   exploded.millisecond = 0;
  39
  40   return Time::FromLocalExploded(exploded);
  41 }
  42
  43 // Returns the boundary value for comparing against the FieldTrial's added
  44 // groups for a given |divisor| (total probability) and |entropy_value|.
  45 FieldTrial::Probability GetGroupBoundaryValue(
  46     FieldTrial::Probability divisor,
  47     double entropy_value) {
  48   // Add a tiny epsilon value to get consistent results when converting floating
  49   // points to int. Without it, boundary values have inconsistent results, e.g.:
  50   //
  51   //   static_cast<FieldTrial::Probability>(100 * 0.56) == 56
  52   //   static_cast<FieldTrial::Probability>(100 * 0.57) == 56
  53   //   static_cast<FieldTrial::Probability>(100 * 0.58) == 57
  54   //   static_cast<FieldTrial::Probability>(100 * 0.59) == 59
  55   const double kEpsilon = 1e-8;
  56   const FieldTrial::Probability result =
  57       static_cast<FieldTrial::Probability>(divisor * entropy_value + kEpsilon);
  58   // Ensure that adding the epsilon still results in a value < |divisor|.
  59   return std::min(result, divisor - 1);
  60 }
  61
  62 }  // namespace
  63
  64 // statics
  65 const int FieldTrial::kNotFinalized = -1;
  66 const int FieldTrial::kDefaultGroupNumber = 0;
  67 bool FieldTrial::enable_benchmarking_ = false;
  68
  69 const char FieldTrialList::kPersistentStringSeparator('/');
  70 int FieldTrialList::kNoExpirationYear = 0;
  71
  72 //------------------------------------------------------------------------------
  73 // FieldTrial methods and members.
  74
  75 FieldTrial::EntropyProvider::~EntropyProvider() {
  76 }
  77
  78 void FieldTrial::Disable() {
  79   DCHECK(!group_reported_);
  80   enable_field_trial_ = false;
  81
  82   // In case we are disabled after initialization, we need to switch
  83   // the trial to the default group.
  84   if (group_ != kNotFinalized) {
  85     // Only reset when not already the default group, because in case we were
  86     // forced to the default group, the group number may not be
  87     // kDefaultGroupNumber, so we should keep it as is.
  88     if (group_name_ != default_group_name_)
  89       SetGroupChoice(default_group_name_, kDefaultGroupNumber);
  90   }
  91 }
  92
  93 int FieldTrial::AppendGroup(const std::string& name,
  94                             Probability group_probability) {
  95   // When the group choice was previously forced, we only need to return the
  96   // the id of the chosen group, and anything can be returned for the others.
  97   if (forced_) {
  98     DCHECK(!group_name_.empty());
  99     if (name == group_name_) {
 100       // Note that while |group_| may be equal to |kDefaultGroupNumber| on the
 101       // forced trial, it will not have the same value as the default group
 102       // number returned from the non-forced |FactoryGetFieldTrial()| call,
 103       // which takes care to ensure that this does not happen.
 104       return group_;
 105     }
 106     DCHECK_NE(next_group_number_, group_);
 107     // We still return different numbers each time, in case some caller need
 108     // them to be different.
 109     return next_group_number_++;
 110   }
 111
 112   DCHECK_LE(group_probability, divisor_);
 113   DCHECK_GE(group_probability, 0);
 114
 115   if (enable_benchmarking_ || !enable_field_trial_)
 116     group_probability = 0;
 117
 118   accumulated_group_probability_ += group_probability;
 119
 120   DCHECK_LE(accumulated_group_probability_, divisor_);
 121   if (group_ == kNotFinalized && accumulated_group_probability_ > random_) {
 122     // This is the group that crossed the random line, so we do the assignment.
 123     SetGroupChoice(name, next_group_number_);
 124   }
 125   return next_group_number_++;
 126 }
 127
 128 int FieldTrial::group() {
 129   FinalizeGroupChoice();
 130   if (trial_registered_)
 131     FieldTrialList::NotifyFieldTrialGroupSelection(this);
 132   return group_;
 133 }
 134
 135 const std::string& FieldTrial::group_name() {
 136   // Call |group()| to ensure group gets assigned and observers are notified.
 137   group();
 138   DCHECK(!group_name_.empty());
 139   return group_name_;
 140 }
 141
 142 void FieldTrial::SetForced() {
 143   // We might have been forced before (e.g., by CreateFieldTrial) and it's
 144   // first come first served, e.g., command line switch has precedence.
 145   if (forced_)
 146     return;
 147
 148   // And we must finalize the group choice before we mark ourselves as forced.
 149   FinalizeGroupChoice();
 150   forced_ = true;
 151 }
 152
 153 // static
 154 void FieldTrial::EnableBenchmarking() {
 155   DCHECK_EQ(0u, FieldTrialList::GetFieldTrialCount());
 156   enable_benchmarking_ = true;
 157 }
 158
 159 // static
 160 FieldTrial* FieldTrial::CreateSimulatedFieldTrial(
 161     const std::string& trial_name,
 162     Probability total_probability,
 163     const std::string& default_group_name,
 164     double entropy_value) {
 165   return new FieldTrial(trial_name, total_probability, default_group_name,
 166                         entropy_value);
 167 }
 168
 169 FieldTrial::FieldTrial(const std::string& trial_name,
 170                        const Probability total_probability,
 171                        const std::string& default_group_name,
 172                        double entropy_value)
 173     : trial_name_(trial_name),
 174       divisor_(total_probability),
 175       default_group_name_(default_group_name),
 176       random_(GetGroupBoundaryValue(total_probability, entropy_value)),
 177       accumulated_group_probability_(0),
 178       next_group_number_(kDefaultGroupNumber + 1),
 179       group_(kNotFinalized),
 180       enable_field_trial_(true),
 181       forced_(false),
 182       group_reported_(false),
 183       trial_registered_(false) {
 184   DCHECK_GT(total_probability, 0);
 185   DCHECK(!trial_name_.empty());
 186   DCHECK(!default_group_name_.empty());
 187 }
 188
 189 FieldTrial::~FieldTrial() {}
 190
 191 void FieldTrial::SetTrialRegistered() {
 192   DCHECK_EQ(kNotFinalized, group_);
 193   DCHECK(!trial_registered_);
 194   trial_registered_ = true;
 195 }
 196
 197 void FieldTrial::SetGroupChoice(const std::string& group_name, int number) {
 198   group_ = number;
 199   if (group_name.empty())
 200     StringAppendF(&group_name_, "%d", group_);
 201   else
 202     group_name_ = group_name;
 203   DVLOG(1) << "Field trial: " << trial_name_ << " Group choice:" << group_name_;
 204 }
 205
 206 void FieldTrial::FinalizeGroupChoice() {
 207   if (group_ != kNotFinalized)
 208     return;
 209   accumulated_group_probability_ = divisor_;
 210   // Here it's OK to use |kDefaultGroupNumber| since we can't be forced and not
 211   // finalized.
 212   DCHECK(!forced_);
 213   SetGroupChoice(default_group_name_, kDefaultGroupNumber);
 214 }
 215
 216 bool FieldTrial::GetActiveGroup(ActiveGroup* active_group) const {
 217   if (!group_reported_ || !enable_field_trial_)
 218     return false;
 219   DCHECK_NE(group_, kNotFinalized);
 220   active_group->trial_name = trial_name_;
 221   active_group->group_name = group_name_;
 222   return true;
 223 }
 224
 225 //------------------------------------------------------------------------------
 226 // FieldTrialList methods and members.
 227
 228 // static
 229 FieldTrialList* FieldTrialList::global_ = NULL;
 230
 231 // static
 232 bool FieldTrialList::used_without_global_ = false;
 233
 234 FieldTrialList::Observer::~Observer() {
 235 }
 236
 237 FieldTrialList::FieldTrialList(
 238     const FieldTrial::EntropyProvider* entropy_provider)
 239     : entropy_provider_(entropy_provider),
 240       observer_list_(new ObserverListThreadSafe<FieldTrialList::Observer>(
 241           ObserverListBase<FieldTrialList::Observer>::NOTIFY_EXISTING_ONLY)) {
 242   DCHECK(!global_);
 243   DCHECK(!used_without_global_);
 244   global_ = this;
 245
 246   Time two_years_from_build_time = GetBuildTime() + TimeDelta::FromDays(730);
 247   Time::Exploded exploded;
 248   two_years_from_build_time.LocalExplode(&exploded);
 249   kNoExpirationYear = exploded.year;
 250 }
 251
 252 FieldTrialList::~FieldTrialList() {
 253   AutoLock auto_lock(lock_);
 254   while (!registered_.empty()) {
 255     RegistrationList::iterator it = registered_.begin();
 256     it->second->Release();
 257     registered_.erase(it->first);
 258   }
 259   DCHECK_EQ(this, global_);
 260   global_ = NULL;
 261 }
 262
 263 // static
 264 FieldTrial* FieldTrialList::FactoryGetFieldTrial(
 265     const std::string& trial_name,
 266     FieldTrial::Probability total_probability,
 267     const std::string& default_group_name,
 268     const int year,
 269     const int month,
 270     const int day_of_month,
 271     FieldTrial::RandomizationType randomization_type,
 272     int* default_group_number) {
 273   return FactoryGetFieldTrialWithRandomizationSeed(
 274       trial_name, total_probability, default_group_name,
 275       year, month, day_of_month, randomization_type, 0, default_group_number);
 276 }
 277
 278 // static
 279 FieldTrial* FieldTrialList::FactoryGetFieldTrialWithRandomizationSeed(
 280     const std::string& trial_name,
 281     FieldTrial::Probability total_probability,
 282     const std::string& default_group_name,
 283     const int year,
 284     const int month,
 285     const int day_of_month,
 286     FieldTrial::RandomizationType randomization_type,
 287     uint32 randomization_seed,
 288     int* default_group_number) {
 289   if (default_group_number)
 290     *default_group_number = FieldTrial::kDefaultGroupNumber;
 291   // Check if the field trial has already been created in some other way.
 292   FieldTrial* existing_trial = Find(trial_name);
 293   if (existing_trial) {
 294     CHECK(existing_trial->forced_);
 295     // If the default group name differs between the existing forced trial
 296     // and this trial, then use a different value for the default group number.
 297     if (default_group_number &&
 298         default_group_name != existing_trial->default_group_name()) {
 299       // If the new default group number corresponds to the group that was
 300       // chosen for the forced trial (which has been finalized when it was
 301       // forced), then set the default group number to that.
 302       if (default_group_name == existing_trial->group_name_internal()) {
 303         *default_group_number = existing_trial->group_;
 304       } else {
 305         // Otherwise, use |kNonConflictingGroupNumber| (-2) for the default
 306         // group number, so that it does not conflict with the |AppendGroup()|
 307         // result for the chosen group.
 308         const int kNonConflictingGroupNumber = -2;
 309         COMPILE_ASSERT(
 310             kNonConflictingGroupNumber != FieldTrial::kDefaultGroupNumber,
 311             conflicting_default_group_number);
 312         COMPILE_ASSERT(
 313             kNonConflictingGroupNumber != FieldTrial::kNotFinalized,
 314             conflicting_default_group_number);
 315         *default_group_number = kNonConflictingGroupNumber;
 316       }
 317     }
 318     return existing_trial;
 319   }
 320
 321   double entropy_value;
 322   if (randomization_type == FieldTrial::ONE_TIME_RANDOMIZED) {
 323     entropy_value = GetEntropyProviderForOneTimeRandomization()->
 324           GetEntropyForTrial(trial_name, randomization_seed);
 325   } else {
 326     DCHECK_EQ(FieldTrial::SESSION_RANDOMIZED, randomization_type);
 327     DCHECK_EQ(0U, randomization_seed);
 328     entropy_value = RandDouble();
 329   }
 330
 331   FieldTrial* field_trial = new FieldTrial(trial_name, total_probability,
 332                                            default_group_name, entropy_value);
 333   if (GetBuildTime() > CreateTimeFromParams(year, month, day_of_month))
 334     field_trial->Disable();
 335   FieldTrialList::Register(field_trial);
 336   return field_trial;
 337 }
 338
 339 // static
 340 FieldTrial* FieldTrialList::Find(const std::string& name) {
 341   if (!global_)
 342     return NULL;
 343   AutoLock auto_lock(global_->lock_);
 344   return global_->PreLockedFind(name);
 345 }
 346
 347 // static
 348 int FieldTrialList::FindValue(const std::string& name) {
 349   FieldTrial* field_trial = Find(name);
 350   if (field_trial)
 351     return field_trial->group();
 352   return FieldTrial::kNotFinalized;
 353 }
 354
 355 // static
 356 std::string FieldTrialList::FindFullName(const std::string& name) {
 357   FieldTrial* field_trial = Find(name);
 358   if (field_trial)
 359     return field_trial->group_name();
 360   return std::string();
 361 }
 362
 363 // static
 364 bool FieldTrialList::TrialExists(const std::string& name) {
 365   return Find(name) != NULL;
 366 }
 367
 368 // static
 369 void FieldTrialList::StatesToString(std::string* output) {
 370   FieldTrial::ActiveGroups active_groups;
 371   GetActiveFieldTrialGroups(&active_groups);
 372   for (FieldTrial::ActiveGroups::const_iterator it = active_groups.begin();
 373        it != active_groups.end(); ++it) {
 374     DCHECK_EQ(std::string::npos,
 375               it->trial_name.find(kPersistentStringSeparator));
 376     DCHECK_EQ(std::string::npos,
 377               it->group_name.find(kPersistentStringSeparator));
 378     output->append(it->trial_name);
 379     output->append(1, kPersistentStringSeparator);
 380     output->append(it->group_name);
 381     output->append(1, kPersistentStringSeparator);
 382   }
 383 }
 384
 385 // static
 386 void FieldTrialList::GetActiveFieldTrialGroups(
 387     FieldTrial::ActiveGroups* active_groups) {
 388   DCHECK(active_groups->empty());
 389   if (!global_)
 390     return;
 391   AutoLock auto_lock(global_->lock_);
 392
 393   for (RegistrationList::iterator it = global_->registered_.begin();
 394        it != global_->registered_.end(); ++it) {
 395     FieldTrial::ActiveGroup active_group;
 396     if (it->second->GetActiveGroup(&active_group))
 397       active_groups->push_back(active_group);
 398   }
 399 }
 400
 401 // static
 402 bool FieldTrialList::CreateTrialsFromString(const std::string& trials_string,
 403                                             FieldTrialActivationMode mode) {
 404   DCHECK(global_);
 405   if (trials_string.empty() || !global_)
 406     return true;
 407
 408   size_t next_item = 0;
 409   while (next_item < trials_string.length()) {
 410     size_t name_end = trials_string.find(kPersistentStringSeparator, next_item);
 411     if (name_end == trials_string.npos || next_item == name_end)
 412       return false;
 413     size_t group_name_end = trials_string.find(kPersistentStringSeparator,
 414                                                name_end + 1);
 415     if (group_name_end == trials_string.npos || name_end + 1 == group_name_end)
 416       return false;
 417     std::string name(trials_string, next_item, name_end - next_item);
 418     std::string group_name(trials_string, name_end + 1,
 419                            group_name_end - name_end - 1);
 420     next_item = group_name_end + 1;
 421
 422     FieldTrial* trial = CreateFieldTrial(name, group_name);
 423     if (!trial)
 424       return false;
 425     if (mode == ACTIVATE_TRIALS) {
 426       // Call |group()| to mark the trial as "used" and notify observers, if
 427       // any. This is useful to ensure that field trials created in child
 428       // processes are properly reported in crash reports.
 429       trial->group();
 430     }
 431   }
 432   return true;
 433 }
 434
 435 // static
 436 FieldTrial* FieldTrialList::CreateFieldTrial(
 437     const std::string& name,
 438     const std::string& group_name) {
 439   DCHECK(global_);
 440   DCHECK_GE(name.size(), 0u);
 441   DCHECK_GE(group_name.size(), 0u);
 442   if (name.empty() || group_name.empty() || !global_)
 443     return NULL;
 444
 445   FieldTrial* field_trial = FieldTrialList::Find(name);
 446   if (field_trial) {
 447     // In single process mode, or when we force them from the command line,
 448     // we may have already created the field trial.
 449     if (field_trial->group_name_internal() != group_name)
 450       return NULL;
 451     return field_trial;
 452   }
 453   const int kTotalProbability = 100;
 454   field_trial = new FieldTrial(name, kTotalProbability, group_name, 0);
 455   FieldTrialList::Register(field_trial);
 456   // Force the trial, which will also finalize the group choice.
 457   field_trial->SetForced();
 458   return field_trial;
 459 }
 460
 461 // static
 462 void FieldTrialList::AddObserver(Observer* observer) {
 463   if (!global_)
 464     return;
 465   global_->observer_list_->AddObserver(observer);
 466 }
 467
 468 // static
 469 void FieldTrialList::RemoveObserver(Observer* observer) {
 470   if (!global_)
 471     return;
 472   global_->observer_list_->RemoveObserver(observer);
 473 }
 474
 475 // static
 476 void FieldTrialList::NotifyFieldTrialGroupSelection(FieldTrial* field_trial) {
 477   if (!global_)
 478     return;
 479
 480   {
 481     AutoLock auto_lock(global_->lock_);
 482     if (field_trial->group_reported_)
 483       return;
 484     field_trial->group_reported_ = true;
 485   }
 486
 487   if (!field_trial->enable_field_trial_)
 488     return;
 489
 490   global_->observer_list_->Notify(
 491       &FieldTrialList::Observer::OnFieldTrialGroupFinalized,
 492       field_trial->trial_name(),
 493       field_trial->group_name_internal());
 494 }
 495
 496 // static
 497 size_t FieldTrialList::GetFieldTrialCount() {
 498   if (!global_)
 499     return 0;
 500   AutoLock auto_lock(global_->lock_);
 501   return global_->registered_.size();
 502 }
 503
 504 // static
 505 const FieldTrial::EntropyProvider*
 506     FieldTrialList::GetEntropyProviderForOneTimeRandomization() {
 507   if (!global_) {
 508     used_without_global_ = true;
 509     return NULL;
 510   }
 511
 512   return global_->entropy_provider_.get();
 513 }
 514
 515 FieldTrial* FieldTrialList::PreLockedFind(const std::string& name) {
 516   RegistrationList::iterator it = registered_.find(name);
 517   if (registered_.end() == it)
 518     return NULL;
 519   return it->second;
 520 }
 521
 522 // static
 523 void FieldTrialList::Register(FieldTrial* trial) {
 524   if (!global_) {
 525     used_without_global_ = true;
 526     return;
 527   }
 528   AutoLock auto_lock(global_->lock_);
 529   DCHECK(!global_->PreLockedFind(trial->trial_name()));
 530   trial->AddRef();
 531   trial->SetTrialRegistered();
 532   global_->registered_[trial->trial_name()] = trial;
 533 }
 534
 535 }  // namespace base