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 const char FieldTrialList::kActivationMarker('*');
  71 int FieldTrialList::kNoExpirationYear = 0;
  72
  73 //------------------------------------------------------------------------------
  74 // FieldTrial methods and members.
  75
  76 FieldTrial::EntropyProvider::~EntropyProvider() {
  77 }
  78
  79 void FieldTrial::Disable() {
  80   DCHECK(!group_reported_);
  81   enable_field_trial_ = false;
  82
  83   // In case we are disabled after initialization, we need to switch
  84   // the trial to the default group.
  85   if (group_ != kNotFinalized) {
  86     // Only reset when not already the default group, because in case we were
  87     // forced to the default group, the group number may not be
  88     // kDefaultGroupNumber, so we should keep it as is.
  89     if (group_name_ != default_group_name_)
  90       SetGroupChoice(default_group_name_, kDefaultGroupNumber);
  91   }
  92 }
  93
  94 int FieldTrial::AppendGroup(const std::string& name,
  95                             Probability group_probability) {
  96   // When the group choice was previously forced, we only need to return the
  97   // the id of the chosen group, and anything can be returned for the others.
  98   if (forced_) {
  99     DCHECK(!group_name_.empty());
 100     if (name == group_name_) {
 101       // Note that while |group_| may be equal to |kDefaultGroupNumber| on the
 102       // forced trial, it will not have the same value as the default group
 103       // number returned from the non-forced |FactoryGetFieldTrial()| call,
 104       // which takes care to ensure that this does not happen.
 105       return group_;
 106     }
 107     DCHECK_NE(next_group_number_, group_);
 108     // We still return different numbers each time, in case some caller need
 109     // them to be different.
 110     return next_group_number_++;
 111   }
 112
 113   DCHECK_LE(group_probability, divisor_);
 114   DCHECK_GE(group_probability, 0);
 115
 116   if (enable_benchmarking_ || !enable_field_trial_)
 117     group_probability = 0;
 118
 119   accumulated_group_probability_ += group_probability;
 120
 121   DCHECK_LE(accumulated_group_probability_, divisor_);
 122   if (group_ == kNotFinalized && accumulated_group_probability_ > random_) {
 123     // This is the group that crossed the random line, so we do the assignment.
 124     SetGroupChoice(name, next_group_number_);
 125   }
 126   return next_group_number_++;
 127 }
 128
 129 int FieldTrial::group() {
 130   FinalizeGroupChoice();
 131   if (trial_registered_)
 132     FieldTrialList::NotifyFieldTrialGroupSelection(this);
 133   return group_;
 134 }
 135
 136 const std::string& FieldTrial::group_name() {
 137   // Call |group()| to ensure group gets assigned and observers are notified.
 138   group();
 139   DCHECK(!group_name_.empty());
 140   return group_name_;
 141 }
 142
 143 void FieldTrial::SetForced() {
 144   // We might have been forced before (e.g., by CreateFieldTrial) and it's
 145   // first come first served, e.g., command line switch has precedence.
 146   if (forced_)
 147     return;
 148
 149   // And we must finalize the group choice before we mark ourselves as forced.
 150   FinalizeGroupChoice();
 151   forced_ = true;
 152 }
 153
 154 // static
 155 void FieldTrial::EnableBenchmarking() {
 156   DCHECK_EQ(0u, FieldTrialList::GetFieldTrialCount());
 157   enable_benchmarking_ = true;
 158 }
 159
 160 // static
 161 FieldTrial* FieldTrial::CreateSimulatedFieldTrial(
 162     const std::string& trial_name,
 163     Probability total_probability,
 164     const std::string& default_group_name,
 165     double entropy_value) {
 166   return new FieldTrial(trial_name, total_probability, default_group_name,
 167                         entropy_value);
 168 }
 169
 170 FieldTrial::FieldTrial(const std::string& trial_name,
 171                        const Probability total_probability,
 172                        const std::string& default_group_name,
 173                        double entropy_value)
 174     : trial_name_(trial_name),
 175       divisor_(total_probability),
 176       default_group_name_(default_group_name),
 177       random_(GetGroupBoundaryValue(total_probability, entropy_value)),
 178       accumulated_group_probability_(0),
 179       next_group_number_(kDefaultGroupNumber + 1),
 180       group_(kNotFinalized),
 181       enable_field_trial_(true),
 182       forced_(false),
 183       group_reported_(false),
 184       trial_registered_(false) {
 185   DCHECK_GT(total_probability, 0);
 186   DCHECK(!trial_name_.empty());
 187   DCHECK(!default_group_name_.empty());
 188 }
 189
 190 FieldTrial::~FieldTrial() {}
 191
 192 void FieldTrial::SetTrialRegistered() {
 193   DCHECK_EQ(kNotFinalized, group_);
 194   DCHECK(!trial_registered_);
 195   trial_registered_ = true;
 196 }
 197
 198 void FieldTrial::SetGroupChoice(const std::string& group_name, int number) {
 199   group_ = number;
 200   if (group_name.empty())
 201     StringAppendF(&group_name_, "%d", group_);
 202   else
 203     group_name_ = group_name;
 204   DVLOG(1) << "Field trial: " << trial_name_ << " Group choice:" << group_name_;
 205 }
 206
 207 void FieldTrial::FinalizeGroupChoice() {
 208   if (group_ != kNotFinalized)
 209     return;
 210   accumulated_group_probability_ = divisor_;
 211   // Here it's OK to use |kDefaultGroupNumber| since we can't be forced and not
 212   // finalized.
 213   DCHECK(!forced_);
 214   SetGroupChoice(default_group_name_, kDefaultGroupNumber);
 215 }
 216
 217 bool FieldTrial::GetActiveGroup(ActiveGroup* active_group) const {
 218   if (!group_reported_ || !enable_field_trial_)
 219     return false;
 220   DCHECK_NE(group_, kNotFinalized);
 221   active_group->trial_name = trial_name_;
 222   active_group->group_name = group_name_;
 223   return true;
 224 }
 225
 226 //------------------------------------------------------------------------------
 227 // FieldTrialList methods and members.
 228
 229 // static
 230 FieldTrialList* FieldTrialList::global_ = NULL;
 231
 232 // static
 233 bool FieldTrialList::used_without_global_ = false;
 234
 235 FieldTrialList::Observer::~Observer() {
 236 }
 237
 238 FieldTrialList::FieldTrialList(
 239     const FieldTrial::EntropyProvider* entropy_provider)
 240     : entropy_provider_(entropy_provider),
 241       observer_list_(new ObserverListThreadSafe<FieldTrialList::Observer>(
 242           ObserverListBase<FieldTrialList::Observer>::NOTIFY_EXISTING_ONLY)) {
 243   DCHECK(!global_);
 244   DCHECK(!used_without_global_);
 245   global_ = this;
 246
 247   Time two_years_from_build_time = GetBuildTime() + TimeDelta::FromDays(730);
 248   Time::Exploded exploded;
 249   two_years_from_build_time.LocalExplode(&exploded);
 250   kNoExpirationYear = exploded.year;
 251 }
 252
 253 FieldTrialList::~FieldTrialList() {
 254   AutoLock auto_lock(lock_);
 255   while (!registered_.empty()) {
 256     RegistrationMap::iterator it = registered_.begin();
 257     it->second->Release();
 258     registered_.erase(it->first);
 259   }
 260   DCHECK_EQ(this, global_);
 261   global_ = NULL;
 262 }
 263
 264 // static
 265 FieldTrial* FieldTrialList::FactoryGetFieldTrial(
 266     const std::string& trial_name,
 267     FieldTrial::Probability total_probability,
 268     const std::string& default_group_name,
 269     const int year,
 270     const int month,
 271     const int day_of_month,
 272     FieldTrial::RandomizationType randomization_type,
 273     int* default_group_number) {
 274   return FactoryGetFieldTrialWithRandomizationSeed(
 275       trial_name, total_probability, default_group_name,
 276       year, month, day_of_month, randomization_type, 0, default_group_number);
 277 }
 278
 279 // static
 280 FieldTrial* FieldTrialList::FactoryGetFieldTrialWithRandomizationSeed(
 281     const std::string& trial_name,
 282     FieldTrial::Probability total_probability,
 283     const std::string& default_group_name,
 284     const int year,
 285     const int month,
 286     const int day_of_month,
 287     FieldTrial::RandomizationType randomization_type,
 288     uint32 randomization_seed,
 289     int* default_group_number) {
 290   if (default_group_number)
 291     *default_group_number = FieldTrial::kDefaultGroupNumber;
 292   // Check if the field trial has already been created in some other way.
 293   FieldTrial* existing_trial = Find(trial_name);
 294   if (existing_trial) {
 295     CHECK(existing_trial->forced_);
 296     // If the default group name differs between the existing forced trial
 297     // and this trial, then use a different value for the default group number.
 298     if (default_group_number &&
 299         default_group_name != existing_trial->default_group_name()) {
 300       // If the new default group number corresponds to the group that was
 301       // chosen for the forced trial (which has been finalized when it was
 302       // forced), then set the default group number to that.
 303       if (default_group_name == existing_trial->group_name_internal()) {
 304         *default_group_number = existing_trial->group_;
 305       } else {
 306         // Otherwise, use |kNonConflictingGroupNumber| (-2) for the default
 307         // group number, so that it does not conflict with the |AppendGroup()|
 308         // result for the chosen group.
 309         const int kNonConflictingGroupNumber = -2;
 310         COMPILE_ASSERT(
 311             kNonConflictingGroupNumber != FieldTrial::kDefaultGroupNumber,
 312             conflicting_default_group_number);
 313         COMPILE_ASSERT(
 314             kNonConflictingGroupNumber != FieldTrial::kNotFinalized,
 315             conflicting_default_group_number);
 316         *default_group_number = kNonConflictingGroupNumber;
 317       }
 318     }
 319     return existing_trial;
 320   }
 321
 322   double entropy_value;
 323   if (randomization_type == FieldTrial::ONE_TIME_RANDOMIZED) {
 324     const FieldTrial::EntropyProvider* entropy_provider =
 325         GetEntropyProviderForOneTimeRandomization();
 326     CHECK(entropy_provider);
 327     entropy_value = entropy_provider->GetEntropyForTrial(trial_name,
 328                                                          randomization_seed);
 329   } else {
 330     DCHECK_EQ(FieldTrial::SESSION_RANDOMIZED, randomization_type);
 331     DCHECK_EQ(0U, randomization_seed);
 332     entropy_value = RandDouble();
 333   }
 334
 335   FieldTrial* field_trial = new FieldTrial(trial_name, total_probability,
 336                                            default_group_name, entropy_value);
 337   if (GetBuildTime() > CreateTimeFromParams(year, month, day_of_month))
 338     field_trial->Disable();
 339   FieldTrialList::Register(field_trial);
 340   return field_trial;
 341 }
 342
 343 // static
 344 FieldTrial* FieldTrialList::Find(const std::string& name) {
 345   if (!global_)
 346     return NULL;
 347   AutoLock auto_lock(global_->lock_);
 348   return global_->PreLockedFind(name);
 349 }
 350
 351 // static
 352 int FieldTrialList::FindValue(const std::string& name) {
 353   FieldTrial* field_trial = Find(name);
 354   if (field_trial)
 355     return field_trial->group();
 356   return FieldTrial::kNotFinalized;
 357 }
 358
 359 // static
 360 std::string FieldTrialList::FindFullName(const std::string& name) {
 361   FieldTrial* field_trial = Find(name);
 362   if (field_trial)
 363     return field_trial->group_name();
 364   return std::string();
 365 }
 366
 367 // static
 368 bool FieldTrialList::TrialExists(const std::string& name) {
 369   return Find(name) != NULL;
 370 }
 371
 372 // static
 373 void FieldTrialList::StatesToString(std::string* output) {
 374   FieldTrial::ActiveGroups active_groups;
 375   GetActiveFieldTrialGroups(&active_groups);
 376   for (FieldTrial::ActiveGroups::const_iterator it = active_groups.begin();
 377        it != active_groups.end(); ++it) {
 378     DCHECK_EQ(std::string::npos,
 379               it->trial_name.find(kPersistentStringSeparator));
 380     DCHECK_EQ(std::string::npos,
 381               it->group_name.find(kPersistentStringSeparator));
 382     output->append(it->trial_name);
 383     output->append(1, kPersistentStringSeparator);
 384     output->append(it->group_name);
 385     output->append(1, kPersistentStringSeparator);
 386   }
 387 }
 388
 389 // static
 390 void FieldTrialList::GetActiveFieldTrialGroups(
 391     FieldTrial::ActiveGroups* active_groups) {
 392   DCHECK(active_groups->empty());
 393   if (!global_)
 394     return;
 395   AutoLock auto_lock(global_->lock_);
 396
 397   for (RegistrationMap::iterator it = global_->registered_.begin();
 398        it != global_->registered_.end(); ++it) {
 399     FieldTrial::ActiveGroup active_group;
 400     if (it->second->GetActiveGroup(&active_group))
 401       active_groups->push_back(active_group);
 402   }
 403 }
 404
 405 // static
 406 bool FieldTrialList::CreateTrialsFromString(
 407     const std::string& trials_string,
 408     FieldTrialActivationMode mode,
 409     const std::set<std::string>& ignored_trial_names) {
 410   DCHECK(global_);
 411   if (trials_string.empty() || !global_)
 412     return true;
 413
 414   size_t next_item = 0;
 415   while (next_item < trials_string.length()) {
 416     size_t name_end = trials_string.find(kPersistentStringSeparator, next_item);
 417     if (name_end == trials_string.npos || next_item == name_end)
 418       return false;
 419     size_t group_name_end = trials_string.find(kPersistentStringSeparator,
 420                                                name_end + 1);
 421     if (name_end + 1 == group_name_end)
 422       return false;
 423     if (group_name_end == trials_string.npos)
 424       group_name_end = trials_string.length();
 425
 426     // Verify if the trial should be activated or not.
 427     std::string name;
 428     bool force_activation = false;
 429     if (trials_string[next_item] == kActivationMarker) {
 430       // Name cannot be only the indicator.
 431       if (name_end - next_item == 1)
 432         return false;
 433       next_item++;
 434       force_activation = true;
 435     }
 436     name.append(trials_string, next_item, name_end - next_item);
 437     std::string group_name(trials_string, name_end + 1,
 438                            group_name_end - name_end - 1);
 439     next_item = group_name_end + 1;
 440
 441     if (ignored_trial_names.find(name) != ignored_trial_names.end())
 442       continue;
 443
 444     FieldTrial* trial = CreateFieldTrial(name, group_name);
 445     if (!trial)
 446       return false;
 447     if (mode == ACTIVATE_TRIALS || force_activation) {
 448       // Call |group()| to mark the trial as "used" and notify observers, if
 449       // any. This is useful to ensure that field trials created in child
 450       // processes are properly reported in crash reports.
 451       trial->group();
 452     }
 453   }
 454   return true;
 455 }
 456
 457 // static
 458 FieldTrial* FieldTrialList::CreateFieldTrial(
 459     const std::string& name,
 460     const std::string& group_name) {
 461   DCHECK(global_);
 462   DCHECK_GE(name.size(), 0u);
 463   DCHECK_GE(group_name.size(), 0u);
 464   if (name.empty() || group_name.empty() || !global_)
 465     return NULL;
 466
 467   FieldTrial* field_trial = FieldTrialList::Find(name);
 468   if (field_trial) {
 469     // In single process mode, or when we force them from the command line,
 470     // we may have already created the field trial.
 471     if (field_trial->group_name_internal() != group_name)
 472       return NULL;
 473     return field_trial;
 474   }
 475   const int kTotalProbability = 100;
 476   field_trial = new FieldTrial(name, kTotalProbability, group_name, 0);
 477   FieldTrialList::Register(field_trial);
 478   // Force the trial, which will also finalize the group choice.
 479   field_trial->SetForced();
 480   return field_trial;
 481 }
 482
 483 // static
 484 void FieldTrialList::AddObserver(Observer* observer) {
 485   if (!global_)
 486     return;
 487   global_->observer_list_->AddObserver(observer);
 488 }
 489
 490 // static
 491 void FieldTrialList::RemoveObserver(Observer* observer) {
 492   if (!global_)
 493     return;
 494   global_->observer_list_->RemoveObserver(observer);
 495 }
 496
 497 // static
 498 void FieldTrialList::NotifyFieldTrialGroupSelection(FieldTrial* field_trial) {
 499   if (!global_)
 500     return;
 501
 502   {
 503     AutoLock auto_lock(global_->lock_);
 504     if (field_trial->group_reported_)
 505       return;
 506     field_trial->group_reported_ = true;
 507   }
 508
 509   if (!field_trial->enable_field_trial_)
 510     return;
 511
 512   global_->observer_list_->Notify(
 513       &FieldTrialList::Observer::OnFieldTrialGroupFinalized,
 514       field_trial->trial_name(),
 515       field_trial->group_name_internal());
 516 }
 517
 518 // static
 519 size_t FieldTrialList::GetFieldTrialCount() {
 520   if (!global_)
 521     return 0;
 522   AutoLock auto_lock(global_->lock_);
 523   return global_->registered_.size();
 524 }
 525
 526 // static
 527 const FieldTrial::EntropyProvider*
 528     FieldTrialList::GetEntropyProviderForOneTimeRandomization() {
 529   if (!global_) {
 530     used_without_global_ = true;
 531     return NULL;
 532   }
 533
 534   return global_->entropy_provider_.get();
 535 }
 536
 537 FieldTrial* FieldTrialList::PreLockedFind(const std::string& name) {
 538   RegistrationMap::iterator it = registered_.find(name);
 539   if (registered_.end() == it)
 540     return NULL;
 541   return it->second;
 542 }
 543
 544 // static
 545 void FieldTrialList::Register(FieldTrial* trial) {
 546   if (!global_) {
 547     used_without_global_ = true;
 548     return;
 549   }
 550   AutoLock auto_lock(global_->lock_);
 551   DCHECK(!global_->PreLockedFind(trial->trial_name()));
 552   trial->AddRef();
 553   trial->SetTrialRegistered();
 554   global_->registered_[trial->trial_name()] = trial;
 555 }
 556
 557 }  // namespace base