base/metrics/histogram.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 // Histogram is an object that aggregates statistics, and can summarize them in
   6 // various forms, including ASCII graphical, HTML, and numerically (as a
   7 // vector of numbers corresponding to each of the aggregating buckets).
   8 // See header file for details and examples.
   9
  10 #include "base/metrics/histogram.h"
  11
  12 #include <math.h>
  13
  14 #include <algorithm>
  15 #include <string>
  16
  17 #include "base/compiler_specific.h"
  18 #include "base/debug/alias.h"
  19 #include "base/logging.h"
  20 #include "base/metrics/histogram_macros.h"
  21 #include "base/metrics/sample_vector.h"
  22 #include "base/metrics/statistics_recorder.h"
  23 #include "base/pickle.h"
  24 #include "base/strings/string_util.h"
  25 #include "base/strings/stringprintf.h"
  26 #include "base/synchronization/lock.h"
  27 #include "base/values.h"
  28
  29 namespace base {
  30
  31 namespace {
  32
  33 bool ReadHistogramArguments(PickleIterator* iter,
  34                             std::string* histogram_name,
  35                             int* flags,
  36                             int* declared_min,
  37                             int* declared_max,
  38                             size_t* bucket_count,
  39                             uint32* range_checksum) {
  40   if (!iter->ReadString(histogram_name) ||
  41       !iter->ReadInt(flags) ||
  42       !iter->ReadInt(declared_min) ||
  43       !iter->ReadInt(declared_max) ||
  44       !iter->ReadSizeT(bucket_count) ||
  45       !iter->ReadUInt32(range_checksum)) {
  46     DLOG(ERROR) << "Pickle error decoding Histogram: " << *histogram_name;
  47     return false;
  48   }
  49
  50   // Since these fields may have come from an untrusted renderer, do additional
  51   // checks above and beyond those in Histogram::Initialize()
  52   if (*declared_max <= 0 ||
  53       *declared_min <= 0 ||
  54       *declared_max < *declared_min ||
  55       INT_MAX / sizeof(HistogramBase::Count) <= *bucket_count ||
  56       *bucket_count < 2) {
  57     DLOG(ERROR) << "Values error decoding Histogram: " << histogram_name;
  58     return false;
  59   }
  60
  61   // We use the arguments to find or create the local version of the histogram
  62   // in this process, so we need to clear the IPC flag.
  63   DCHECK(*flags & HistogramBase::kIPCSerializationSourceFlag);
  64   *flags &= ~HistogramBase::kIPCSerializationSourceFlag;
  65
  66   return true;
  67 }
  68
  69 bool ValidateRangeChecksum(const HistogramBase& histogram,
  70                            uint32 range_checksum) {
  71   const Histogram& casted_histogram =
  72       static_cast<const Histogram&>(histogram);
  73
  74   return casted_histogram.bucket_ranges()->checksum() == range_checksum;
  75 }
  76
  77 }  // namespace
  78
  79 typedef HistogramBase::Count Count;
  80 typedef HistogramBase::Sample Sample;
  81
  82 // static
  83 const size_t Histogram::kBucketCount_MAX = 16384u;
  84
  85 HistogramBase* Histogram::FactoryGet(const std::string& name,
  86                                      Sample minimum,
  87                                      Sample maximum,
  88                                      size_t bucket_count,
  89                                      int32 flags) {
  90   bool valid_arguments =
  91       InspectConstructionArguments(name, &minimum, &maximum, &bucket_count);
  92   DCHECK(valid_arguments);
  93
  94   HistogramBase* histogram = StatisticsRecorder::FindHistogram(name);
  95   if (!histogram) {
  96     // To avoid racy destruction at shutdown, the following will be leaked.
  97     BucketRanges* ranges = new BucketRanges(bucket_count + 1);
  98     InitializeBucketRanges(minimum, maximum, ranges);
  99     const BucketRanges* registered_ranges =
 100         StatisticsRecorder::RegisterOrDeleteDuplicateRanges(ranges);
 101
 102     Histogram* tentative_histogram =
 103         new Histogram(name, minimum, maximum, registered_ranges);
 104
 105     tentative_histogram->SetFlags(flags);
 106     histogram =
 107         StatisticsRecorder::RegisterOrDeleteDuplicate(tentative_histogram);
 108   }
 109
 110   DCHECK_EQ(HISTOGRAM, histogram->GetHistogramType());
 111   if (!histogram->HasConstructionArguments(minimum, maximum, bucket_count)) {
 112     // The construction arguments do not match the existing histogram.  This can
 113     // come about if an extension updates in the middle of a chrome run and has
 114     // changed one of them, or simply by bad code within Chrome itself.  We
 115     // return NULL here with the expectation that bad code in Chrome will crash
 116     // on dereference, but extension/Pepper APIs will guard against NULL and not
 117     // crash.
 118     DLOG(ERROR) << "Histogram " << name << " has bad construction arguments";
 119     return NULL;
 120   }
 121   return histogram;
 122 }
 123
 124 HistogramBase* Histogram::FactoryTimeGet(const std::string& name,
 125                                          TimeDelta minimum,
 126                                          TimeDelta maximum,
 127                                          size_t bucket_count,
 128                                          int32 flags) {
 129   return FactoryGet(name, static_cast<Sample>(minimum.InMilliseconds()),
 130                     static_cast<Sample>(maximum.InMilliseconds()), bucket_count,
 131                     flags);
 132 }
 133
 134 HistogramBase* Histogram::FactoryGet(const char* name,
 135                                      Sample minimum,
 136                                      Sample maximum,
 137                                      size_t bucket_count,
 138                                      int32 flags) {
 139   return FactoryGet(std::string(name), minimum, maximum, bucket_count, flags);
 140 }
 141
 142 HistogramBase* Histogram::FactoryTimeGet(const char* name,
 143                                          TimeDelta minimum,
 144                                          TimeDelta maximum,
 145                                          size_t bucket_count,
 146                                          int32 flags) {
 147   return FactoryTimeGet(std::string(name), minimum, maximum, bucket_count,
 148                         flags);
 149 }
 150
 151 // Calculate what range of values are held in each bucket.
 152 // We have to be careful that we don't pick a ratio between starting points in
 153 // consecutive buckets that is sooo small, that the integer bounds are the same
 154 // (effectively making one bucket get no values).  We need to avoid:
 155 //   ranges(i) == ranges(i + 1)
 156 // To avoid that, we just do a fine-grained bucket width as far as we need to
 157 // until we get a ratio that moves us along at least 2 units at a time.  From
 158 // that bucket onward we do use the exponential growth of buckets.
 159 //
 160 // static
 161 void Histogram::InitializeBucketRanges(Sample minimum,
 162                                        Sample maximum,
 163                                        BucketRanges* ranges) {
 164   double log_max = log(static_cast<double>(maximum));
 165   double log_ratio;
 166   double log_next;
 167   size_t bucket_index = 1;
 168   Sample current = minimum;
 169   ranges->set_range(bucket_index, current);
 170   size_t bucket_count = ranges->bucket_count();
 171   while (bucket_count > ++bucket_index) {
 172     double log_current;
 173     log_current = log(static_cast<double>(current));
 174     // Calculate the count'th root of the range.
 175     log_ratio = (log_max - log_current) / (bucket_count - bucket_index);
 176     // See where the next bucket would start.
 177     log_next = log_current + log_ratio;
 178     Sample next;
 179     next = static_cast<int>(floor(exp(log_next) + 0.5));
 180     if (next > current)
 181       current = next;
 182     else
 183       ++current;  // Just do a narrow bucket, and keep trying.
 184     ranges->set_range(bucket_index, current);
 185   }
 186   ranges->set_range(ranges->bucket_count(), HistogramBase::kSampleType_MAX);
 187   ranges->ResetChecksum();
 188 }
 189
 190 // static
 191 const int Histogram::kCommonRaceBasedCountMismatch = 5;
 192
 193 int Histogram::FindCorruption(const HistogramSamples& samples) const {
 194   int inconsistencies = NO_INCONSISTENCIES;
 195   Sample previous_range = -1;  // Bottom range is always 0.
 196   for (size_t index = 0; index < bucket_count(); ++index) {
 197     int new_range = ranges(index);
 198     if (previous_range >= new_range)
 199       inconsistencies |= BUCKET_ORDER_ERROR;
 200     previous_range = new_range;
 201   }
 202
 203   if (!bucket_ranges()->HasValidChecksum())
 204     inconsistencies |= RANGE_CHECKSUM_ERROR;
 205
 206   int64 delta64 = samples.redundant_count() - samples.TotalCount();
 207   if (delta64 != 0) {
 208     int delta = static_cast<int>(delta64);
 209     if (delta != delta64)
 210       delta = INT_MAX;  // Flag all giant errors as INT_MAX.
 211     if (delta > 0) {
 212       UMA_HISTOGRAM_COUNTS("Histogram.InconsistentCountHigh", delta);
 213       if (delta > kCommonRaceBasedCountMismatch)
 214         inconsistencies |= COUNT_HIGH_ERROR;
 215     } else {
 216       DCHECK_GT(0, delta);
 217       UMA_HISTOGRAM_COUNTS("Histogram.InconsistentCountLow", -delta);
 218       if (-delta > kCommonRaceBasedCountMismatch)
 219         inconsistencies |= COUNT_LOW_ERROR;
 220     }
 221   }
 222   return inconsistencies;
 223 }
 224
 225 Sample Histogram::ranges(size_t i) const {
 226   return bucket_ranges_->range(i);
 227 }
 228
 229 size_t Histogram::bucket_count() const {
 230   return bucket_ranges_->bucket_count();
 231 }
 232
 233 // static
 234 bool Histogram::InspectConstructionArguments(const std::string& name,
 235                                              Sample* minimum,
 236                                              Sample* maximum,
 237                                              size_t* bucket_count) {
 238   // Defensive code for backward compatibility.
 239   if (*minimum < 1) {
 240     DVLOG(1) << "Histogram: " << name << " has bad minimum: " << *minimum;
 241     *minimum = 1;
 242   }
 243   if (*maximum >= kSampleType_MAX) {
 244     DVLOG(1) << "Histogram: " << name << " has bad maximum: " << *maximum;
 245     *maximum = kSampleType_MAX - 1;
 246   }
 247   if (*bucket_count >= kBucketCount_MAX) {
 248     DVLOG(1) << "Histogram: " << name << " has bad bucket_count: "
 249              << *bucket_count;
 250     *bucket_count = kBucketCount_MAX - 1;
 251   }
 252
 253   if (*minimum >= *maximum)
 254     return false;
 255   if (*bucket_count < 3)
 256     return false;
 257   if (*bucket_count > static_cast<size_t>(*maximum - *minimum + 2))
 258     return false;
 259   return true;
 260 }
 261
 262 HistogramType Histogram::GetHistogramType() const {
 263   return HISTOGRAM;
 264 }
 265
 266 bool Histogram::HasConstructionArguments(Sample expected_minimum,
 267                                          Sample expected_maximum,
 268                                          size_t expected_bucket_count) const {
 269   return ((expected_minimum == declared_min_) &&
 270           (expected_maximum == declared_max_) &&
 271           (expected_bucket_count == bucket_count()));
 272 }
 273
 274 void Histogram::Add(int value) {
 275   DCHECK_EQ(0, ranges(0));
 276   DCHECK_EQ(kSampleType_MAX, ranges(bucket_count()));
 277
 278   if (value > kSampleType_MAX - 1)
 279     value = kSampleType_MAX - 1;
 280   if (value < 0)
 281     value = 0;
 282   samples_->Accumulate(value, 1);
 283 }
 284
 285 scoped_ptr<HistogramSamples> Histogram::SnapshotSamples() const {
 286   return SnapshotSampleVector().Pass();
 287 }
 288
 289 void Histogram::AddSamples(const HistogramSamples& samples) {
 290   samples_->Add(samples);
 291 }
 292
 293 bool Histogram::AddSamplesFromPickle(PickleIterator* iter) {
 294   return samples_->AddFromPickle(iter);
 295 }
 296
 297 // The following methods provide a graphical histogram display.
 298 void Histogram::WriteHTMLGraph(std::string* output) const {
 299   // TBD(jar) Write a nice HTML bar chart, with divs an mouse-overs etc.
 300   output->append("<PRE>");
 301   WriteAsciiImpl(true, "<br>", output);
 302   output->append("</PRE>");
 303 }
 304
 305 void Histogram::WriteAscii(std::string* output) const {
 306   WriteAsciiImpl(true, "\n", output);
 307 }
 308
 309 bool Histogram::SerializeInfoImpl(Pickle* pickle) const {
 310   DCHECK(bucket_ranges()->HasValidChecksum());
 311   return pickle->WriteString(histogram_name()) &&
 312       pickle->WriteInt(flags()) &&
 313       pickle->WriteInt(declared_min()) &&
 314       pickle->WriteInt(declared_max()) &&
 315       pickle->WriteSizeT(bucket_count()) &&
 316       pickle->WriteUInt32(bucket_ranges()->checksum());
 317 }
 318
 319 Histogram::Histogram(const std::string& name,
 320                      Sample minimum,
 321                      Sample maximum,
 322                      const BucketRanges* ranges)
 323   : HistogramBase(name),
 324     bucket_ranges_(ranges),
 325     declared_min_(minimum),
 326     declared_max_(maximum) {
 327   if (ranges)
 328     samples_.reset(new SampleVector(ranges));
 329 }
 330
 331 Histogram::~Histogram() {
 332 }
 333
 334 bool Histogram::PrintEmptyBucket(size_t index) const {
 335   return true;
 336 }
 337
 338 // Use the actual bucket widths (like a linear histogram) until the widths get
 339 // over some transition value, and then use that transition width.  Exponentials
 340 // get so big so fast (and we don't expect to see a lot of entries in the large
 341 // buckets), so we need this to make it possible to see what is going on and
 342 // not have 0-graphical-height buckets.
 343 double Histogram::GetBucketSize(Count current, size_t i) const {
 344   DCHECK_GT(ranges(i + 1), ranges(i));
 345   static const double kTransitionWidth = 5;
 346   double denominator = ranges(i + 1) - ranges(i);
 347   if (denominator > kTransitionWidth)
 348     denominator = kTransitionWidth;  // Stop trying to normalize.
 349   return current/denominator;
 350 }
 351
 352 const std::string Histogram::GetAsciiBucketRange(size_t i) const {
 353   return GetSimpleAsciiBucketRange(ranges(i));
 354 }
 355
 356 //------------------------------------------------------------------------------
 357 // Private methods
 358
 359 // static
 360 HistogramBase* Histogram::DeserializeInfoImpl(PickleIterator* iter) {
 361   std::string histogram_name;
 362   int flags;
 363   int declared_min;
 364   int declared_max;
 365   size_t bucket_count;
 366   uint32 range_checksum;
 367
 368   if (!ReadHistogramArguments(iter, &histogram_name, &flags, &declared_min,
 369                               &declared_max, &bucket_count, &range_checksum)) {
 370     return NULL;
 371   }
 372
 373   // Find or create the local version of the histogram in this process.
 374   HistogramBase* histogram = Histogram::FactoryGet(
 375       histogram_name, declared_min, declared_max, bucket_count, flags);
 376
 377   if (!ValidateRangeChecksum(*histogram, range_checksum)) {
 378     // The serialized histogram might be corrupted.
 379     return NULL;
 380   }
 381   return histogram;
 382 }
 383
 384 scoped_ptr<SampleVector> Histogram::SnapshotSampleVector() const {
 385   scoped_ptr<SampleVector> samples(new SampleVector(bucket_ranges()));
 386   samples->Add(*samples_);
 387   return samples.Pass();
 388 }
 389
 390 void Histogram::WriteAsciiImpl(bool graph_it,
 391                                const std::string& newline,
 392                                std::string* output) const {
 393   // Get local (stack) copies of all effectively volatile class data so that we
 394   // are consistent across our output activities.
 395   scoped_ptr<SampleVector> snapshot = SnapshotSampleVector();
 396   Count sample_count = snapshot->TotalCount();
 397
 398   WriteAsciiHeader(*snapshot, sample_count, output);
 399   output->append(newline);
 400
 401   // Prepare to normalize graphical rendering of bucket contents.
 402   double max_size = 0;
 403   if (graph_it)
 404     max_size = GetPeakBucketSize(*snapshot);
 405
 406   // Calculate space needed to print bucket range numbers.  Leave room to print
 407   // nearly the largest bucket range without sliding over the histogram.
 408   size_t largest_non_empty_bucket = bucket_count() - 1;
 409   while (0 == snapshot->GetCountAtIndex(largest_non_empty_bucket)) {
 410     if (0 == largest_non_empty_bucket)
 411       break;  // All buckets are empty.
 412     --largest_non_empty_bucket;
 413   }
 414
 415   // Calculate largest print width needed for any of our bucket range displays.
 416   size_t print_width = 1;
 417   for (size_t i = 0; i < bucket_count(); ++i) {
 418     if (snapshot->GetCountAtIndex(i)) {
 419       size_t width = GetAsciiBucketRange(i).size() + 1;
 420       if (width > print_width)
 421         print_width = width;
 422     }
 423   }
 424
 425   int64 remaining = sample_count;
 426   int64 past = 0;
 427   // Output the actual histogram graph.
 428   for (size_t i = 0; i < bucket_count(); ++i) {
 429     Count current = snapshot->GetCountAtIndex(i);
 430     if (!current && !PrintEmptyBucket(i))
 431       continue;
 432     remaining -= current;
 433     std::string range = GetAsciiBucketRange(i);
 434     output->append(range);
 435     for (size_t j = 0; range.size() + j < print_width + 1; ++j)
 436       output->push_back(' ');
 437     if (0 == current && i < bucket_count() - 1 &&
 438         0 == snapshot->GetCountAtIndex(i + 1)) {
 439       while (i < bucket_count() - 1 &&
 440              0 == snapshot->GetCountAtIndex(i + 1)) {
 441         ++i;
 442       }
 443       output->append("... ");
 444       output->append(newline);
 445       continue;  // No reason to plot emptiness.
 446     }
 447     double current_size = GetBucketSize(current, i);
 448     if (graph_it)
 449       WriteAsciiBucketGraph(current_size, max_size, output);
 450     WriteAsciiBucketContext(past, current, remaining, i, output);
 451     output->append(newline);
 452     past += current;
 453   }
 454   DCHECK_EQ(sample_count, past);
 455 }
 456
 457 double Histogram::GetPeakBucketSize(const SampleVector& samples) const {
 458   double max = 0;
 459   for (size_t i = 0; i < bucket_count() ; ++i) {
 460     double current_size = GetBucketSize(samples.GetCountAtIndex(i), i);
 461     if (current_size > max)
 462       max = current_size;
 463   }
 464   return max;
 465 }
 466
 467 void Histogram::WriteAsciiHeader(const SampleVector& samples,
 468                                  Count sample_count,
 469                                  std::string* output) const {
 470   StringAppendF(output,
 471                 "Histogram: %s recorded %d samples",
 472                 histogram_name().c_str(),
 473                 sample_count);
 474   if (0 == sample_count) {
 475     DCHECK_EQ(samples.sum(), 0);
 476   } else {
 477     double average = static_cast<float>(samples.sum()) / sample_count;
 478
 479     StringAppendF(output, ", average = %.1f", average);
 480   }
 481   if (flags() & ~kHexRangePrintingFlag)
 482     StringAppendF(output, " (flags = 0x%x)", flags() & ~kHexRangePrintingFlag);
 483 }
 484
 485 void Histogram::WriteAsciiBucketContext(const int64 past,
 486                                         const Count current,
 487                                         const int64 remaining,
 488                                         const size_t i,
 489                                         std::string* output) const {
 490   double scaled_sum = (past + current + remaining) / 100.0;
 491   WriteAsciiBucketValue(current, scaled_sum, output);
 492   if (0 < i) {
 493     double percentage = past / scaled_sum;
 494     StringAppendF(output, " {%3.1f%%}", percentage);
 495   }
 496 }
 497
 498 void Histogram::GetParameters(DictionaryValue* params) const {
 499   params->SetString("type", HistogramTypeToString(GetHistogramType()));
 500   params->SetInteger("min", declared_min());
 501   params->SetInteger("max", declared_max());
 502   params->SetInteger("bucket_count", static_cast<int>(bucket_count()));
 503 }
 504
 505 void Histogram::GetCountAndBucketData(Count* count,
 506                                       int64* sum,
 507                                       ListValue* buckets) const {
 508   scoped_ptr<SampleVector> snapshot = SnapshotSampleVector();
 509   *count = snapshot->TotalCount();
 510   *sum = snapshot->sum();
 511   size_t index = 0;
 512   for (size_t i = 0; i < bucket_count(); ++i) {
 513     Sample count_at_index = snapshot->GetCountAtIndex(i);
 514     if (count_at_index > 0) {
 515       scoped_ptr<DictionaryValue> bucket_value(new DictionaryValue());
 516       bucket_value->SetInteger("low", ranges(i));
 517       if (i != bucket_count() - 1)
 518         bucket_value->SetInteger("high", ranges(i + 1));
 519       bucket_value->SetInteger("count", count_at_index);
 520       buckets->Set(index, bucket_value.release());
 521       ++index;
 522     }
 523   }
 524 }
 525
 526 //------------------------------------------------------------------------------
 527 // LinearHistogram: This histogram uses a traditional set of evenly spaced
 528 // buckets.
 529 //------------------------------------------------------------------------------
 530
 531 LinearHistogram::~LinearHistogram() {}
 532
 533 HistogramBase* LinearHistogram::FactoryGet(const std::string& name,
 534                                            Sample minimum,
 535                                            Sample maximum,
 536                                            size_t bucket_count,
 537                                            int32 flags) {
 538   return FactoryGetWithRangeDescription(
 539       name, minimum, maximum, bucket_count, flags, NULL);
 540 }
 541
 542 HistogramBase* LinearHistogram::FactoryTimeGet(const std::string& name,
 543                                                TimeDelta minimum,
 544                                                TimeDelta maximum,
 545                                                size_t bucket_count,
 546                                                int32 flags) {
 547   return FactoryGet(name, static_cast<Sample>(minimum.InMilliseconds()),
 548                     static_cast<Sample>(maximum.InMilliseconds()), bucket_count,
 549                     flags);
 550 }
 551
 552 HistogramBase* LinearHistogram::FactoryGet(const char* name,
 553                                            Sample minimum,
 554                                            Sample maximum,
 555                                            size_t bucket_count,
 556                                            int32 flags) {
 557   return FactoryGet(std::string(name), minimum, maximum, bucket_count, flags);
 558 }
 559
 560 HistogramBase* LinearHistogram::FactoryTimeGet(const char* name,
 561                                                TimeDelta minimum,
 562                                                TimeDelta maximum,
 563                                                size_t bucket_count,
 564                                                int32 flags) {
 565   return FactoryTimeGet(std::string(name),  minimum, maximum, bucket_count,
 566                         flags);
 567 }
 568
 569 HistogramBase* LinearHistogram::FactoryGetWithRangeDescription(
 570       const std::string& name,
 571       Sample minimum,
 572       Sample maximum,
 573       size_t bucket_count,
 574       int32 flags,
 575       const DescriptionPair descriptions[]) {
 576   bool valid_arguments = Histogram::InspectConstructionArguments(
 577       name, &minimum, &maximum, &bucket_count);
 578   DCHECK(valid_arguments);
 579
 580   HistogramBase* histogram = StatisticsRecorder::FindHistogram(name);
 581   if (!histogram) {
 582     // To avoid racy destruction at shutdown, the following will be leaked.
 583     BucketRanges* ranges = new BucketRanges(bucket_count + 1);
 584     InitializeBucketRanges(minimum, maximum, ranges);
 585     const BucketRanges* registered_ranges =
 586         StatisticsRecorder::RegisterOrDeleteDuplicateRanges(ranges);
 587
 588     LinearHistogram* tentative_histogram =
 589         new LinearHistogram(name, minimum, maximum, registered_ranges);
 590
 591     // Set range descriptions.
 592     if (descriptions) {
 593       for (int i = 0; descriptions[i].description; ++i) {
 594         tentative_histogram->bucket_description_[descriptions[i].sample] =
 595             descriptions[i].description;
 596       }
 597     }
 598
 599     tentative_histogram->SetFlags(flags);
 600     histogram =
 601         StatisticsRecorder::RegisterOrDeleteDuplicate(tentative_histogram);
 602   }
 603
 604   DCHECK_EQ(LINEAR_HISTOGRAM, histogram->GetHistogramType());
 605   if (!histogram->HasConstructionArguments(minimum, maximum, bucket_count)) {
 606     // The construction arguments do not match the existing histogram.  This can
 607     // come about if an extension updates in the middle of a chrome run and has
 608     // changed one of them, or simply by bad code within Chrome itself.  We
 609     // return NULL here with the expectation that bad code in Chrome will crash
 610     // on dereference, but extension/Pepper APIs will guard against NULL and not
 611     // crash.
 612     DLOG(ERROR) << "Histogram " << name << " has bad construction arguments";
 613     return NULL;
 614   }
 615   return histogram;
 616 }
 617
 618 HistogramType LinearHistogram::GetHistogramType() const {
 619   return LINEAR_HISTOGRAM;
 620 }
 621
 622 LinearHistogram::LinearHistogram(const std::string& name,
 623                                  Sample minimum,
 624                                  Sample maximum,
 625                                  const BucketRanges* ranges)
 626     : Histogram(name, minimum, maximum, ranges) {
 627 }
 628
 629 double LinearHistogram::GetBucketSize(Count current, size_t i) const {
 630   DCHECK_GT(ranges(i + 1), ranges(i));
 631   // Adjacent buckets with different widths would have "surprisingly" many (few)
 632   // samples in a histogram if we didn't normalize this way.
 633   double denominator = ranges(i + 1) - ranges(i);
 634   return current/denominator;
 635 }
 636
 637 const std::string LinearHistogram::GetAsciiBucketRange(size_t i) const {
 638   int range = ranges(i);
 639   BucketDescriptionMap::const_iterator it = bucket_description_.find(range);
 640   if (it == bucket_description_.end())
 641     return Histogram::GetAsciiBucketRange(i);
 642   return it->second;
 643 }
 644
 645 bool LinearHistogram::PrintEmptyBucket(size_t index) const {
 646   return bucket_description_.find(ranges(index)) == bucket_description_.end();
 647 }
 648
 649 // static
 650 void LinearHistogram::InitializeBucketRanges(Sample minimum,
 651                                              Sample maximum,
 652                                              BucketRanges* ranges) {
 653   double min = minimum;
 654   double max = maximum;
 655   size_t bucket_count = ranges->bucket_count();
 656   for (size_t i = 1; i < bucket_count; ++i) {
 657     double linear_range =
 658         (min * (bucket_count - 1 - i) + max * (i - 1)) / (bucket_count - 2);
 659     ranges->set_range(i, static_cast<Sample>(linear_range + 0.5));
 660   }
 661   ranges->set_range(ranges->bucket_count(), HistogramBase::kSampleType_MAX);
 662   ranges->ResetChecksum();
 663 }
 664
 665 // static
 666 HistogramBase* LinearHistogram::DeserializeInfoImpl(PickleIterator* iter) {
 667   std::string histogram_name;
 668   int flags;
 669   int declared_min;
 670   int declared_max;
 671   size_t bucket_count;
 672   uint32 range_checksum;
 673
 674   if (!ReadHistogramArguments(iter, &histogram_name, &flags, &declared_min,
 675                               &declared_max, &bucket_count, &range_checksum)) {
 676     return NULL;
 677   }
 678
 679   HistogramBase* histogram = LinearHistogram::FactoryGet(
 680       histogram_name, declared_min, declared_max, bucket_count, flags);
 681   if (!ValidateRangeChecksum(*histogram, range_checksum)) {
 682     // The serialized histogram might be corrupted.
 683     return NULL;
 684   }
 685   return histogram;
 686 }
 687
 688 //------------------------------------------------------------------------------
 689 // This section provides implementation for BooleanHistogram.
 690 //------------------------------------------------------------------------------
 691
 692 HistogramBase* BooleanHistogram::FactoryGet(const std::string& name,
 693                                             int32 flags) {
 694   HistogramBase* histogram = StatisticsRecorder::FindHistogram(name);
 695   if (!histogram) {
 696     // To avoid racy destruction at shutdown, the following will be leaked.
 697     BucketRanges* ranges = new BucketRanges(4);
 698     LinearHistogram::InitializeBucketRanges(1, 2, ranges);
 699     const BucketRanges* registered_ranges =
 700         StatisticsRecorder::RegisterOrDeleteDuplicateRanges(ranges);
 701
 702     BooleanHistogram* tentative_histogram =
 703         new BooleanHistogram(name, registered_ranges);
 704
 705     tentative_histogram->SetFlags(flags);
 706     histogram =
 707         StatisticsRecorder::RegisterOrDeleteDuplicate(tentative_histogram);
 708   }
 709
 710   DCHECK_EQ(BOOLEAN_HISTOGRAM, histogram->GetHistogramType());
 711   return histogram;
 712 }
 713
 714 HistogramBase* BooleanHistogram::FactoryGet(const char* name, int32 flags) {
 715   return FactoryGet(std::string(name), flags);
 716 }
 717
 718 HistogramType BooleanHistogram::GetHistogramType() const {
 719   return BOOLEAN_HISTOGRAM;
 720 }
 721
 722 BooleanHistogram::BooleanHistogram(const std::string& name,
 723                                    const BucketRanges* ranges)
 724     : LinearHistogram(name, 1, 2, ranges) {}
 725
 726 HistogramBase* BooleanHistogram::DeserializeInfoImpl(PickleIterator* iter) {
 727   std::string histogram_name;
 728   int flags;
 729   int declared_min;
 730   int declared_max;
 731   size_t bucket_count;
 732   uint32 range_checksum;
 733
 734   if (!ReadHistogramArguments(iter, &histogram_name, &flags, &declared_min,
 735                               &declared_max, &bucket_count, &range_checksum)) {
 736     return NULL;
 737   }
 738
 739   HistogramBase* histogram = BooleanHistogram::FactoryGet(
 740       histogram_name, flags);
 741   if (!ValidateRangeChecksum(*histogram, range_checksum)) {
 742     // The serialized histogram might be corrupted.
 743     return NULL;
 744   }
 745   return histogram;
 746 }
 747
 748 //------------------------------------------------------------------------------
 749 // CustomHistogram:
 750 //------------------------------------------------------------------------------
 751
 752 HistogramBase* CustomHistogram::FactoryGet(
 753     const std::string& name,
 754     const std::vector<Sample>& custom_ranges,
 755     int32 flags) {
 756   CHECK(ValidateCustomRanges(custom_ranges));
 757
 758   HistogramBase* histogram = StatisticsRecorder::FindHistogram(name);
 759   if (!histogram) {
 760     BucketRanges* ranges = CreateBucketRangesFromCustomRanges(custom_ranges);
 761     const BucketRanges* registered_ranges =
 762         StatisticsRecorder::RegisterOrDeleteDuplicateRanges(ranges);
 763
 764     // To avoid racy destruction at shutdown, the following will be leaked.
 765     CustomHistogram* tentative_histogram =
 766         new CustomHistogram(name, registered_ranges);
 767
 768     tentative_histogram->SetFlags(flags);
 769
 770     histogram =
 771         StatisticsRecorder::RegisterOrDeleteDuplicate(tentative_histogram);
 772   }
 773
 774   DCHECK_EQ(histogram->GetHistogramType(), CUSTOM_HISTOGRAM);
 775   return histogram;
 776 }
 777
 778 HistogramBase* CustomHistogram::FactoryGet(
 779     const char* name,
 780     const std::vector<Sample>& custom_ranges,
 781     int32 flags) {
 782   return FactoryGet(std::string(name), custom_ranges, flags);
 783 }
 784
 785 HistogramType CustomHistogram::GetHistogramType() const {
 786   return CUSTOM_HISTOGRAM;
 787 }
 788
 789 // static
 790 std::vector<Sample> CustomHistogram::ArrayToCustomRanges(
 791     const Sample* values, size_t num_values) {
 792   std::vector<Sample> all_values;
 793   for (size_t i = 0; i < num_values; ++i) {
 794     Sample value = values[i];
 795     all_values.push_back(value);
 796
 797     // Ensure that a guard bucket is added. If we end up with duplicate
 798     // values, FactoryGet will take care of removing them.
 799     all_values.push_back(value + 1);
 800   }
 801   return all_values;
 802 }
 803
 804 CustomHistogram::CustomHistogram(const std::string& name,
 805                                  const BucketRanges* ranges)
 806     : Histogram(name,
 807                 ranges->range(1),
 808                 ranges->range(ranges->bucket_count() - 1),
 809                 ranges) {}
 810
 811 bool CustomHistogram::SerializeInfoImpl(Pickle* pickle) const {
 812   if (!Histogram::SerializeInfoImpl(pickle))
 813     return false;
 814
 815   // Serialize ranges. First and last ranges are alwasy 0 and INT_MAX, so don't
 816   // write them.
 817   for (size_t i = 1; i < bucket_ranges()->bucket_count(); ++i) {
 818     if (!pickle->WriteInt(bucket_ranges()->range(i)))
 819       return false;
 820   }
 821   return true;
 822 }
 823
 824 double CustomHistogram::GetBucketSize(Count current, size_t i) const {
 825   return 1;
 826 }
 827
 828 // static
 829 HistogramBase* CustomHistogram::DeserializeInfoImpl(PickleIterator* iter) {
 830   std::string histogram_name;
 831   int flags;
 832   int declared_min;
 833   int declared_max;
 834   size_t bucket_count;
 835   uint32 range_checksum;
 836
 837   if (!ReadHistogramArguments(iter, &histogram_name, &flags, &declared_min,
 838                               &declared_max, &bucket_count, &range_checksum)) {
 839     return NULL;
 840   }
 841
 842   // First and last ranges are not serialized.
 843   std::vector<Sample> sample_ranges(bucket_count - 1);
 844
 845   for (size_t i = 0; i < sample_ranges.size(); ++i) {
 846     if (!iter->ReadInt(&sample_ranges[i]))
 847       return NULL;
 848   }
 849
 850   HistogramBase* histogram = CustomHistogram::FactoryGet(
 851       histogram_name, sample_ranges, flags);
 852   if (!ValidateRangeChecksum(*histogram, range_checksum)) {
 853     // The serialized histogram might be corrupted.
 854     return NULL;
 855   }
 856   return histogram;
 857 }
 858
 859 // static
 860 bool CustomHistogram::ValidateCustomRanges(
 861     const std::vector<Sample>& custom_ranges) {
 862   bool has_valid_range = false;
 863   for (size_t i = 0; i < custom_ranges.size(); i++) {
 864     Sample sample = custom_ranges[i];
 865     if (sample < 0 || sample > HistogramBase::kSampleType_MAX - 1)
 866       return false;
 867     if (sample != 0)
 868       has_valid_range = true;
 869   }
 870   return has_valid_range;
 871 }
 872
 873 // static
 874 BucketRanges* CustomHistogram::CreateBucketRangesFromCustomRanges(
 875       const std::vector<Sample>& custom_ranges) {
 876   // Remove the duplicates in the custom ranges array.
 877   std::vector<int> ranges = custom_ranges;
 878   ranges.push_back(0);  // Ensure we have a zero value.
 879   ranges.push_back(HistogramBase::kSampleType_MAX);
 880   std::sort(ranges.begin(), ranges.end());
 881   ranges.erase(std::unique(ranges.begin(), ranges.end()), ranges.end());
 882
 883   BucketRanges* bucket_ranges = new BucketRanges(ranges.size());
 884   for (size_t i = 0; i < ranges.size(); i++) {
 885     bucket_ranges->set_range(i, ranges[i]);
 886   }
 887   bucket_ranges->ResetChecksum();
 888   return bucket_ranges;
 889 }
 890
 891 }  // namespace base