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      1 // Copyright (c) 2011 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/logging.h"
     18 #include "base/pickle.h"
     19 #include "base/stringprintf.h"
     20 #include "base/synchronization/lock.h"
     21 
     22 namespace base {
     23 
     24 // Static table of checksums for all possible 8 bit bytes.
     25 const uint32 Histogram::kCrcTable[256] = {0x0, 0x77073096L, 0xee0e612cL,
     26 0x990951baL, 0x76dc419L, 0x706af48fL, 0xe963a535L, 0x9e6495a3L, 0xedb8832L,
     27 0x79dcb8a4L, 0xe0d5e91eL, 0x97d2d988L, 0x9b64c2bL, 0x7eb17cbdL, 0xe7b82d07L,
     28 0x90bf1d91L, 0x1db71064L, 0x6ab020f2L, 0xf3b97148L, 0x84be41deL, 0x1adad47dL,
     29 0x6ddde4ebL, 0xf4d4b551L, 0x83d385c7L, 0x136c9856L, 0x646ba8c0L, 0xfd62f97aL,
     30 0x8a65c9ecL, 0x14015c4fL, 0x63066cd9L, 0xfa0f3d63L, 0x8d080df5L, 0x3b6e20c8L,
     31 0x4c69105eL, 0xd56041e4L, 0xa2677172L, 0x3c03e4d1L, 0x4b04d447L, 0xd20d85fdL,
     32 0xa50ab56bL, 0x35b5a8faL, 0x42b2986cL, 0xdbbbc9d6L, 0xacbcf940L, 0x32d86ce3L,
     33 0x45df5c75L, 0xdcd60dcfL, 0xabd13d59L, 0x26d930acL, 0x51de003aL, 0xc8d75180L,
     34 0xbfd06116L, 0x21b4f4b5L, 0x56b3c423L, 0xcfba9599L, 0xb8bda50fL, 0x2802b89eL,
     35 0x5f058808L, 0xc60cd9b2L, 0xb10be924L, 0x2f6f7c87L, 0x58684c11L, 0xc1611dabL,
     36 0xb6662d3dL, 0x76dc4190L, 0x1db7106L, 0x98d220bcL, 0xefd5102aL, 0x71b18589L,
     37 0x6b6b51fL, 0x9fbfe4a5L, 0xe8b8d433L, 0x7807c9a2L, 0xf00f934L, 0x9609a88eL,
     38 0xe10e9818L, 0x7f6a0dbbL, 0x86d3d2dL, 0x91646c97L, 0xe6635c01L, 0x6b6b51f4L,
     39 0x1c6c6162L, 0x856530d8L, 0xf262004eL, 0x6c0695edL, 0x1b01a57bL, 0x8208f4c1L,
     40 0xf50fc457L, 0x65b0d9c6L, 0x12b7e950L, 0x8bbeb8eaL, 0xfcb9887cL, 0x62dd1ddfL,
     41 0x15da2d49L, 0x8cd37cf3L, 0xfbd44c65L, 0x4db26158L, 0x3ab551ceL, 0xa3bc0074L,
     42 0xd4bb30e2L, 0x4adfa541L, 0x3dd895d7L, 0xa4d1c46dL, 0xd3d6f4fbL, 0x4369e96aL,
     43 0x346ed9fcL, 0xad678846L, 0xda60b8d0L, 0x44042d73L, 0x33031de5L, 0xaa0a4c5fL,
     44 0xdd0d7cc9L, 0x5005713cL, 0x270241aaL, 0xbe0b1010L, 0xc90c2086L, 0x5768b525L,
     45 0x206f85b3L, 0xb966d409L, 0xce61e49fL, 0x5edef90eL, 0x29d9c998L, 0xb0d09822L,
     46 0xc7d7a8b4L, 0x59b33d17L, 0x2eb40d81L, 0xb7bd5c3bL, 0xc0ba6cadL, 0xedb88320L,
     47 0x9abfb3b6L, 0x3b6e20cL, 0x74b1d29aL, 0xead54739L, 0x9dd277afL, 0x4db2615L,
     48 0x73dc1683L, 0xe3630b12L, 0x94643b84L, 0xd6d6a3eL, 0x7a6a5aa8L, 0xe40ecf0bL,
     49 0x9309ff9dL, 0xa00ae27L, 0x7d079eb1L, 0xf00f9344L, 0x8708a3d2L, 0x1e01f268L,
     50 0x6906c2feL, 0xf762575dL, 0x806567cbL, 0x196c3671L, 0x6e6b06e7L, 0xfed41b76L,
     51 0x89d32be0L, 0x10da7a5aL, 0x67dd4accL, 0xf9b9df6fL, 0x8ebeeff9L, 0x17b7be43L,
     52 0x60b08ed5L, 0xd6d6a3e8L, 0xa1d1937eL, 0x38d8c2c4L, 0x4fdff252L, 0xd1bb67f1L,
     53 0xa6bc5767L, 0x3fb506ddL, 0x48b2364bL, 0xd80d2bdaL, 0xaf0a1b4cL, 0x36034af6L,
     54 0x41047a60L, 0xdf60efc3L, 0xa867df55L, 0x316e8eefL, 0x4669be79L, 0xcb61b38cL,
     55 0xbc66831aL, 0x256fd2a0L, 0x5268e236L, 0xcc0c7795L, 0xbb0b4703L, 0x220216b9L,
     56 0x5505262fL, 0xc5ba3bbeL, 0xb2bd0b28L, 0x2bb45a92L, 0x5cb36a04L, 0xc2d7ffa7L,
     57 0xb5d0cf31L, 0x2cd99e8bL, 0x5bdeae1dL, 0x9b64c2b0L, 0xec63f226L, 0x756aa39cL,
     58 0x26d930aL, 0x9c0906a9L, 0xeb0e363fL, 0x72076785L, 0x5005713L, 0x95bf4a82L,
     59 0xe2b87a14L, 0x7bb12baeL, 0xcb61b38L, 0x92d28e9bL, 0xe5d5be0dL, 0x7cdcefb7L,
     60 0xbdbdf21L, 0x86d3d2d4L, 0xf1d4e242L, 0x68ddb3f8L, 0x1fda836eL, 0x81be16cdL,
     61 0xf6b9265bL, 0x6fb077e1L, 0x18b74777L, 0x88085ae6L, 0xff0f6a70L, 0x66063bcaL,
     62 0x11010b5cL, 0x8f659effL, 0xf862ae69L, 0x616bffd3L, 0x166ccf45L, 0xa00ae278L,
     63 0xd70dd2eeL, 0x4e048354L, 0x3903b3c2L, 0xa7672661L, 0xd06016f7L, 0x4969474dL,
     64 0x3e6e77dbL, 0xaed16a4aL, 0xd9d65adcL, 0x40df0b66L, 0x37d83bf0L, 0xa9bcae53L,
     65 0xdebb9ec5L, 0x47b2cf7fL, 0x30b5ffe9L, 0xbdbdf21cL, 0xcabac28aL, 0x53b39330L,
     66 0x24b4a3a6L, 0xbad03605L, 0xcdd70693L, 0x54de5729L, 0x23d967bfL, 0xb3667a2eL,
     67 0xc4614ab8L, 0x5d681b02L, 0x2a6f2b94L, 0xb40bbe37L, 0xc30c8ea1L, 0x5a05df1bL,
     68 0x2d02ef8dL,
     69 };
     70 
     71 typedef Histogram::Count Count;
     72 
     73 // static
     74 const size_t Histogram::kBucketCount_MAX = 16384u;
     75 
     76 Histogram* Histogram::FactoryGet(const std::string& name,
     77                                  Sample minimum,
     78                                  Sample maximum,
     79                                  size_t bucket_count,
     80                                  Flags flags) {
     81   Histogram* histogram(NULL);
     82 
     83   // Defensive code.
     84   if (minimum < 1)
     85     minimum = 1;
     86   if (maximum > kSampleType_MAX - 1)
     87     maximum = kSampleType_MAX - 1;
     88 
     89   if (!StatisticsRecorder::FindHistogram(name, &histogram)) {
     90     // Extra variable is not needed... but this keeps this section basically
     91     // identical to other derived classes in this file (and compiler will
     92     // optimize away the extra variable.
     93     // To avoid racy destruction at shutdown, the following will be leaked.
     94     Histogram* tentative_histogram =
     95         new Histogram(name, minimum, maximum, bucket_count);
     96     tentative_histogram->InitializeBucketRange();
     97     tentative_histogram->SetFlags(flags);
     98     histogram =
     99         StatisticsRecorder::RegisterOrDeleteDuplicate(tentative_histogram);
    100   }
    101 
    102   DCHECK_EQ(HISTOGRAM, histogram->histogram_type());
    103   DCHECK(histogram->HasConstructorArguments(minimum, maximum, bucket_count));
    104   return histogram;
    105 }
    106 
    107 Histogram* Histogram::FactoryTimeGet(const std::string& name,
    108                                      TimeDelta minimum,
    109                                      TimeDelta maximum,
    110                                      size_t bucket_count,
    111                                      Flags flags) {
    112   return FactoryGet(name, minimum.InMilliseconds(), maximum.InMilliseconds(),
    113                     bucket_count, flags);
    114 }
    115 
    116 void Histogram::Add(int value) {
    117   if (value > kSampleType_MAX - 1)
    118     value = kSampleType_MAX - 1;
    119   if (value < 0)
    120     value = 0;
    121   size_t index = BucketIndex(value);
    122   DCHECK_GE(value, ranges(index));
    123   DCHECK_LT(value, ranges(index + 1));
    124   Accumulate(value, 1, index);
    125 }
    126 
    127 void Histogram::AddBoolean(bool value) {
    128   DCHECK(false);
    129 }
    130 
    131 void Histogram::AddSampleSet(const SampleSet& sample) {
    132   sample_.Add(sample);
    133 }
    134 
    135 void Histogram::SetRangeDescriptions(const DescriptionPair descriptions[]) {
    136   DCHECK(false);
    137 }
    138 
    139 // The following methods provide a graphical histogram display.
    140 void Histogram::WriteHTMLGraph(std::string* output) const {
    141   // TBD(jar) Write a nice HTML bar chart, with divs an mouse-overs etc.
    142   output->append("<PRE>");
    143   WriteAscii(true, "<br>", output);
    144   output->append("</PRE>");
    145 }
    146 
    147 void Histogram::WriteAscii(bool graph_it, const std::string& newline,
    148                            std::string* output) const {
    149   // Get local (stack) copies of all effectively volatile class data so that we
    150   // are consistent across our output activities.
    151   SampleSet snapshot;
    152   SnapshotSample(&snapshot);
    153   Count sample_count = snapshot.TotalCount();
    154 
    155   WriteAsciiHeader(snapshot, sample_count, output);
    156   output->append(newline);
    157 
    158   // Prepare to normalize graphical rendering of bucket contents.
    159   double max_size = 0;
    160   if (graph_it)
    161     max_size = GetPeakBucketSize(snapshot);
    162 
    163   // Calculate space needed to print bucket range numbers.  Leave room to print
    164   // nearly the largest bucket range without sliding over the histogram.
    165   size_t largest_non_empty_bucket = bucket_count() - 1;
    166   while (0 == snapshot.counts(largest_non_empty_bucket)) {
    167     if (0 == largest_non_empty_bucket)
    168       break;  // All buckets are empty.
    169     --largest_non_empty_bucket;
    170   }
    171 
    172   // Calculate largest print width needed for any of our bucket range displays.
    173   size_t print_width = 1;
    174   for (size_t i = 0; i < bucket_count(); ++i) {
    175     if (snapshot.counts(i)) {
    176       size_t width = GetAsciiBucketRange(i).size() + 1;
    177       if (width > print_width)
    178         print_width = width;
    179     }
    180   }
    181 
    182   int64 remaining = sample_count;
    183   int64 past = 0;
    184   // Output the actual histogram graph.
    185   for (size_t i = 0; i < bucket_count(); ++i) {
    186     Count current = snapshot.counts(i);
    187     if (!current && !PrintEmptyBucket(i))
    188       continue;
    189     remaining -= current;
    190     std::string range = GetAsciiBucketRange(i);
    191     output->append(range);
    192     for (size_t j = 0; range.size() + j < print_width + 1; ++j)
    193       output->push_back(' ');
    194     if (0 == current && i < bucket_count() - 1 && 0 == snapshot.counts(i + 1)) {
    195       while (i < bucket_count() - 1 && 0 == snapshot.counts(i + 1))
    196         ++i;
    197       output->append("... ");
    198       output->append(newline);
    199       continue;  // No reason to plot emptiness.
    200     }
    201     double current_size = GetBucketSize(current, i);
    202     if (graph_it)
    203       WriteAsciiBucketGraph(current_size, max_size, output);
    204     WriteAsciiBucketContext(past, current, remaining, i, output);
    205     output->append(newline);
    206     past += current;
    207   }
    208   DCHECK_EQ(sample_count, past);
    209 }
    210 
    211 // static
    212 std::string Histogram::SerializeHistogramInfo(const Histogram& histogram,
    213                                               const SampleSet& snapshot) {
    214   DCHECK_NE(NOT_VALID_IN_RENDERER, histogram.histogram_type());
    215 
    216   Pickle pickle;
    217   pickle.WriteString(histogram.histogram_name());
    218   pickle.WriteInt(histogram.declared_min());
    219   pickle.WriteInt(histogram.declared_max());
    220   pickle.WriteSize(histogram.bucket_count());
    221   pickle.WriteUInt32(histogram.range_checksum());
    222   pickle.WriteInt(histogram.histogram_type());
    223   pickle.WriteInt(histogram.flags());
    224 
    225   snapshot.Serialize(&pickle);
    226   return std::string(static_cast<const char*>(pickle.data()), pickle.size());
    227 }
    228 
    229 // static
    230 bool Histogram::DeserializeHistogramInfo(const std::string& histogram_info) {
    231   if (histogram_info.empty()) {
    232       return false;
    233   }
    234 
    235   Pickle pickle(histogram_info.data(),
    236                 static_cast<int>(histogram_info.size()));
    237   std::string histogram_name;
    238   int declared_min;
    239   int declared_max;
    240   size_t bucket_count;
    241   uint32 range_checksum;
    242   int histogram_type;
    243   int pickle_flags;
    244   SampleSet sample;
    245 
    246   void* iter = NULL;
    247   if (!pickle.ReadString(&iter, &histogram_name) ||
    248       !pickle.ReadInt(&iter, &declared_min) ||
    249       !pickle.ReadInt(&iter, &declared_max) ||
    250       !pickle.ReadSize(&iter, &bucket_count) ||
    251       !pickle.ReadUInt32(&iter, &range_checksum) ||
    252       !pickle.ReadInt(&iter, &histogram_type) ||
    253       !pickle.ReadInt(&iter, &pickle_flags) ||
    254       !sample.Histogram::SampleSet::Deserialize(&iter, pickle)) {
    255     LOG(ERROR) << "Pickle error decoding Histogram: " << histogram_name;
    256     return false;
    257   }
    258   DCHECK(pickle_flags & kIPCSerializationSourceFlag);
    259   // Since these fields may have come from an untrusted renderer, do additional
    260   // checks above and beyond those in Histogram::Initialize()
    261   if (declared_max <= 0 || declared_min <= 0 || declared_max < declared_min ||
    262       INT_MAX / sizeof(Count) <= bucket_count || bucket_count < 2) {
    263     LOG(ERROR) << "Values error decoding Histogram: " << histogram_name;
    264     return false;
    265   }
    266 
    267   Flags flags = static_cast<Flags>(pickle_flags & ~kIPCSerializationSourceFlag);
    268 
    269   DCHECK_NE(NOT_VALID_IN_RENDERER, histogram_type);
    270 
    271   Histogram* render_histogram(NULL);
    272 
    273   if (histogram_type == HISTOGRAM) {
    274     render_histogram = Histogram::FactoryGet(
    275         histogram_name, declared_min, declared_max, bucket_count, flags);
    276   } else if (histogram_type == LINEAR_HISTOGRAM) {
    277     render_histogram = LinearHistogram::FactoryGet(
    278         histogram_name, declared_min, declared_max, bucket_count, flags);
    279   } else if (histogram_type == BOOLEAN_HISTOGRAM) {
    280     render_histogram = BooleanHistogram::FactoryGet(histogram_name, flags);
    281   } else {
    282     LOG(ERROR) << "Error Deserializing Histogram Unknown histogram_type: "
    283                << histogram_type;
    284     return false;
    285   }
    286 
    287   DCHECK_EQ(render_histogram->declared_min(), declared_min);
    288   DCHECK_EQ(render_histogram->declared_max(), declared_max);
    289   DCHECK_EQ(render_histogram->bucket_count(), bucket_count);
    290   DCHECK_EQ(render_histogram->range_checksum(), range_checksum);
    291   DCHECK_EQ(render_histogram->histogram_type(), histogram_type);
    292 
    293   if (render_histogram->flags() & kIPCSerializationSourceFlag) {
    294     DVLOG(1) << "Single process mode, histogram observed and not copied: "
    295              << histogram_name;
    296   } else {
    297     DCHECK_EQ(flags & render_histogram->flags(), flags);
    298     render_histogram->AddSampleSet(sample);
    299   }
    300 
    301   return true;
    302 }
    303 
    304 //------------------------------------------------------------------------------
    305 // Methods for the validating a sample and a related histogram.
    306 //------------------------------------------------------------------------------
    307 
    308 Histogram::Inconsistencies Histogram::FindCorruption(
    309     const SampleSet& snapshot) const {
    310   int inconsistencies = NO_INCONSISTENCIES;
    311   Sample previous_range = -1;  // Bottom range is always 0.
    312   int64 count = 0;
    313   for (size_t index = 0; index < bucket_count(); ++index) {
    314     count += snapshot.counts(index);
    315     int new_range = ranges(index);
    316     if (previous_range >= new_range)
    317       inconsistencies |= BUCKET_ORDER_ERROR;
    318     previous_range = new_range;
    319   }
    320 
    321   if (!HasValidRangeChecksum())
    322     inconsistencies |= RANGE_CHECKSUM_ERROR;
    323 
    324   int64 delta64 = snapshot.redundant_count() - count;
    325   if (delta64 != 0) {
    326     int delta = static_cast<int>(delta64);
    327     if (delta != delta64)
    328       delta = INT_MAX;  // Flag all giant errors as INT_MAX.
    329     // Since snapshots of histograms are taken asynchronously relative to
    330     // sampling (and snapped from different threads), it is pretty likely that
    331     // we'll catch a redundant count that doesn't match the sample count.  We
    332     // allow for a certain amount of slop before flagging this as an
    333     // inconsistency.  Even with an inconsistency, we'll snapshot it again (for
    334     // UMA in about a half hour, so we'll eventually get the data, if it was
    335     // not the result of a corruption.  If histograms show that 1 is "too tight"
    336     // then we may try to use 2 or 3 for this slop value.
    337     const int kCommonRaceBasedCountMismatch = 1;
    338     if (delta > 0) {
    339       UMA_HISTOGRAM_COUNTS("Histogram.InconsistentCountHigh", delta);
    340       if (delta > kCommonRaceBasedCountMismatch)
    341         inconsistencies |= COUNT_HIGH_ERROR;
    342     } else {
    343       DCHECK_GT(0, delta);
    344       UMA_HISTOGRAM_COUNTS("Histogram.InconsistentCountLow", -delta);
    345       if (-delta > kCommonRaceBasedCountMismatch)
    346         inconsistencies |= COUNT_LOW_ERROR;
    347     }
    348   }
    349   return static_cast<Inconsistencies>(inconsistencies);
    350 }
    351 
    352 Histogram::ClassType Histogram::histogram_type() const {
    353   return HISTOGRAM;
    354 }
    355 
    356 Histogram::Sample Histogram::ranges(size_t i) const {
    357   return ranges_[i];
    358 }
    359 
    360 size_t Histogram::bucket_count() const {
    361   return bucket_count_;
    362 }
    363 
    364 // Do a safe atomic snapshot of sample data.
    365 // This implementation assumes we are on a safe single thread.
    366 void Histogram::SnapshotSample(SampleSet* sample) const {
    367   // Note locking not done in this version!!!
    368   *sample = sample_;
    369 }
    370 
    371 bool Histogram::HasConstructorArguments(Sample minimum,
    372                                         Sample maximum,
    373                                         size_t bucket_count) {
    374   return ((minimum == declared_min_) && (maximum == declared_max_) &&
    375           (bucket_count == bucket_count_));
    376 }
    377 
    378 bool Histogram::HasConstructorTimeDeltaArguments(TimeDelta minimum,
    379                                                  TimeDelta maximum,
    380                                                  size_t bucket_count) {
    381   return ((minimum.InMilliseconds() == declared_min_) &&
    382           (maximum.InMilliseconds() == declared_max_) &&
    383           (bucket_count == bucket_count_));
    384 }
    385 
    386 bool Histogram::HasValidRangeChecksum() const {
    387   return CalculateRangeChecksum() == range_checksum_;
    388 }
    389 
    390 Histogram::Histogram(const std::string& name, Sample minimum,
    391                      Sample maximum, size_t bucket_count)
    392   : histogram_name_(name),
    393     declared_min_(minimum),
    394     declared_max_(maximum),
    395     bucket_count_(bucket_count),
    396     flags_(kNoFlags),
    397     ranges_(bucket_count + 1, 0),
    398     range_checksum_(0),
    399     sample_() {
    400   Initialize();
    401 }
    402 
    403 Histogram::Histogram(const std::string& name, TimeDelta minimum,
    404                      TimeDelta maximum, size_t bucket_count)
    405   : histogram_name_(name),
    406     declared_min_(static_cast<int> (minimum.InMilliseconds())),
    407     declared_max_(static_cast<int> (maximum.InMilliseconds())),
    408     bucket_count_(bucket_count),
    409     flags_(kNoFlags),
    410     ranges_(bucket_count + 1, 0),
    411     range_checksum_(0),
    412     sample_() {
    413   Initialize();
    414 }
    415 
    416 Histogram::~Histogram() {
    417   if (StatisticsRecorder::dump_on_exit()) {
    418     std::string output;
    419     WriteAscii(true, "\n", &output);
    420     LOG(INFO) << output;
    421   }
    422 
    423   // Just to make sure most derived class did this properly...
    424   DCHECK(ValidateBucketRanges());
    425 }
    426 
    427 // Calculate what range of values are held in each bucket.
    428 // We have to be careful that we don't pick a ratio between starting points in
    429 // consecutive buckets that is sooo small, that the integer bounds are the same
    430 // (effectively making one bucket get no values).  We need to avoid:
    431 //   ranges_[i] == ranges_[i + 1]
    432 // To avoid that, we just do a fine-grained bucket width as far as we need to
    433 // until we get a ratio that moves us along at least 2 units at a time.  From
    434 // that bucket onward we do use the exponential growth of buckets.
    435 void Histogram::InitializeBucketRange() {
    436   double log_max = log(static_cast<double>(declared_max()));
    437   double log_ratio;
    438   double log_next;
    439   size_t bucket_index = 1;
    440   Sample current = declared_min();
    441   SetBucketRange(bucket_index, current);
    442   while (bucket_count() > ++bucket_index) {
    443     double log_current;
    444     log_current = log(static_cast<double>(current));
    445     // Calculate the count'th root of the range.
    446     log_ratio = (log_max - log_current) / (bucket_count() - bucket_index);
    447     // See where the next bucket would start.
    448     log_next = log_current + log_ratio;
    449     int next;
    450     next = static_cast<int>(floor(exp(log_next) + 0.5));
    451     if (next > current)
    452       current = next;
    453     else
    454       ++current;  // Just do a narrow bucket, and keep trying.
    455     SetBucketRange(bucket_index, current);
    456   }
    457   ResetRangeChecksum();
    458 
    459   DCHECK_EQ(bucket_count(), bucket_index);
    460 }
    461 
    462 bool Histogram::PrintEmptyBucket(size_t index) const {
    463   return true;
    464 }
    465 
    466 size_t Histogram::BucketIndex(Sample value) const {
    467   // Use simple binary search.  This is very general, but there are better
    468   // approaches if we knew that the buckets were linearly distributed.
    469   DCHECK_LE(ranges(0), value);
    470   DCHECK_GT(ranges(bucket_count()), value);
    471   size_t under = 0;
    472   size_t over = bucket_count();
    473   size_t mid;
    474 
    475   do {
    476     DCHECK_GE(over, under);
    477     mid = under + (over - under)/2;
    478     if (mid == under)
    479       break;
    480     if (ranges(mid) <= value)
    481       under = mid;
    482     else
    483       over = mid;
    484   } while (true);
    485 
    486   DCHECK_LE(ranges(mid), value);
    487   CHECK_GT(ranges(mid+1), value);
    488   return mid;
    489 }
    490 
    491 // Use the actual bucket widths (like a linear histogram) until the widths get
    492 // over some transition value, and then use that transition width.  Exponentials
    493 // get so big so fast (and we don't expect to see a lot of entries in the large
    494 // buckets), so we need this to make it possible to see what is going on and
    495 // not have 0-graphical-height buckets.
    496 double Histogram::GetBucketSize(Count current, size_t i) const {
    497   DCHECK_GT(ranges(i + 1), ranges(i));
    498   static const double kTransitionWidth = 5;
    499   double denominator = ranges(i + 1) - ranges(i);
    500   if (denominator > kTransitionWidth)
    501     denominator = kTransitionWidth;  // Stop trying to normalize.
    502   return current/denominator;
    503 }
    504 
    505 void Histogram::ResetRangeChecksum() {
    506   range_checksum_ = CalculateRangeChecksum();
    507 }
    508 
    509 const std::string Histogram::GetAsciiBucketRange(size_t i) const {
    510   std::string result;
    511   if (kHexRangePrintingFlag & flags_)
    512     StringAppendF(&result, "%#x", ranges(i));
    513   else
    514     StringAppendF(&result, "%d", ranges(i));
    515   return result;
    516 }
    517 
    518 // Update histogram data with new sample.
    519 void Histogram::Accumulate(Sample value, Count count, size_t index) {
    520   // Note locking not done in this version!!!
    521   sample_.Accumulate(value, count, index);
    522 }
    523 
    524 void Histogram::SetBucketRange(size_t i, Sample value) {
    525   DCHECK_GT(bucket_count_, i);
    526   ranges_[i] = value;
    527 }
    528 
    529 bool Histogram::ValidateBucketRanges() const {
    530   // Standard assertions that all bucket ranges should satisfy.
    531   DCHECK_EQ(bucket_count_ + 1, ranges_.size());
    532   DCHECK_EQ(0, ranges_[0]);
    533   DCHECK_EQ(declared_min(), ranges_[1]);
    534   DCHECK_EQ(declared_max(), ranges_[bucket_count_ - 1]);
    535   DCHECK_EQ(kSampleType_MAX, ranges_[bucket_count_]);
    536   return true;
    537 }
    538 
    539 uint32 Histogram::CalculateRangeChecksum() const {
    540   DCHECK_EQ(ranges_.size(), bucket_count() + 1);
    541   uint32 checksum = static_cast<uint32>(ranges_.size());  // Seed checksum.
    542   for (size_t index = 0; index < bucket_count(); ++index)
    543     checksum = Crc32(checksum, ranges(index));
    544   return checksum;
    545 }
    546 
    547 void Histogram::Initialize() {
    548   sample_.Resize(*this);
    549   if (declared_min_ < 1)
    550     declared_min_ = 1;
    551   if (declared_max_ > kSampleType_MAX - 1)
    552     declared_max_ = kSampleType_MAX - 1;
    553   DCHECK_LE(declared_min_, declared_max_);
    554   DCHECK_GT(bucket_count_, 1u);
    555   CHECK_LT(bucket_count_, kBucketCount_MAX);
    556   size_t maximal_bucket_count = declared_max_ - declared_min_ + 2;
    557   DCHECK_LE(bucket_count_, maximal_bucket_count);
    558   DCHECK_EQ(0, ranges_[0]);
    559   ranges_[bucket_count_] = kSampleType_MAX;
    560 }
    561 
    562 // We generate the CRC-32 using the low order bits to select whether to XOR in
    563 // the reversed polynomial 0xedb88320L.  This is nice and simple, and allows us
    564 // to keep the quotient in a uint32.  Since we're not concerned about the nature
    565 // of corruptions (i.e., we don't care about bit sequencing, since we are
    566 // handling memory changes, which are more grotesque) so we don't bother to
    567 // get the CRC correct for big-endian vs little-ending calculations.  All we
    568 // need is a nice hash, that tends to depend on all the bits of the sample, with
    569 // very little chance of changes in one place impacting changes in another
    570 // place.
    571 uint32 Histogram::Crc32(uint32 sum, Histogram::Sample range) {
    572   const bool kUseRealCrc = true;  // TODO(jar): Switch to false and watch stats.
    573   if (kUseRealCrc) {
    574     union {
    575       Histogram::Sample range;
    576       unsigned char bytes[sizeof(Histogram::Sample)];
    577     } converter;
    578     converter.range = range;
    579     for (size_t i = 0; i < sizeof(converter); ++i)
    580       sum = kCrcTable[(sum & 0xff) ^ converter.bytes[i]] ^ (sum >> 8);
    581   } else {
    582     // Use hash techniques provided in ReallyFastHash, except we don't care
    583     // about "avalanching" (which would worsten the hash, and add collisions),
    584     // and we don't care about edge cases since we have an even number of bytes.
    585     union {
    586       Histogram::Sample range;
    587       uint16 ints[sizeof(Histogram::Sample) / 2];
    588     } converter;
    589     DCHECK_EQ(sizeof(Histogram::Sample), sizeof(converter));
    590     converter.range = range;
    591     sum += converter.ints[0];
    592     sum = (sum << 16) ^ sum ^ (static_cast<uint32>(converter.ints[1]) << 11);
    593     sum += sum >> 11;
    594   }
    595   return sum;
    596 }
    597 
    598 //------------------------------------------------------------------------------
    599 // Private methods
    600 
    601 double Histogram::GetPeakBucketSize(const SampleSet& snapshot) const {
    602   double max = 0;
    603   for (size_t i = 0; i < bucket_count() ; ++i) {
    604     double current_size = GetBucketSize(snapshot.counts(i), i);
    605     if (current_size > max)
    606       max = current_size;
    607   }
    608   return max;
    609 }
    610 
    611 void Histogram::WriteAsciiHeader(const SampleSet& snapshot,
    612                                  Count sample_count,
    613                                  std::string* output) const {
    614   StringAppendF(output,
    615                 "Histogram: %s recorded %d samples",
    616                 histogram_name().c_str(),
    617                 sample_count);
    618   if (0 == sample_count) {
    619     DCHECK_EQ(snapshot.sum(), 0);
    620   } else {
    621     double average = static_cast<float>(snapshot.sum()) / sample_count;
    622 
    623     StringAppendF(output, ", average = %.1f", average);
    624   }
    625   if (flags_ & ~kHexRangePrintingFlag)
    626     StringAppendF(output, " (flags = 0x%x)", flags_ & ~kHexRangePrintingFlag);
    627 }
    628 
    629 void Histogram::WriteAsciiBucketContext(const int64 past,
    630                                         const Count current,
    631                                         const int64 remaining,
    632                                         const size_t i,
    633                                         std::string* output) const {
    634   double scaled_sum = (past + current + remaining) / 100.0;
    635   WriteAsciiBucketValue(current, scaled_sum, output);
    636   if (0 < i) {
    637     double percentage = past / scaled_sum;
    638     StringAppendF(output, " {%3.1f%%}", percentage);
    639   }
    640 }
    641 
    642 void Histogram::WriteAsciiBucketValue(Count current, double scaled_sum,
    643                                       std::string* output) const {
    644   StringAppendF(output, " (%d = %3.1f%%)", current, current/scaled_sum);
    645 }
    646 
    647 void Histogram::WriteAsciiBucketGraph(double current_size, double max_size,
    648                                       std::string* output) const {
    649   const int k_line_length = 72;  // Maximal horizontal width of graph.
    650   int x_count = static_cast<int>(k_line_length * (current_size / max_size)
    651                                  + 0.5);
    652   int x_remainder = k_line_length - x_count;
    653 
    654   while (0 < x_count--)
    655     output->append("-");
    656   output->append("O");
    657   while (0 < x_remainder--)
    658     output->append(" ");
    659 }
    660 
    661 //------------------------------------------------------------------------------
    662 // Methods for the Histogram::SampleSet class
    663 //------------------------------------------------------------------------------
    664 
    665 Histogram::SampleSet::SampleSet()
    666     : counts_(),
    667       sum_(0),
    668       redundant_count_(0) {
    669 }
    670 
    671 Histogram::SampleSet::~SampleSet() {
    672 }
    673 
    674 void Histogram::SampleSet::Resize(const Histogram& histogram) {
    675   counts_.resize(histogram.bucket_count(), 0);
    676 }
    677 
    678 void Histogram::SampleSet::CheckSize(const Histogram& histogram) const {
    679   DCHECK_EQ(histogram.bucket_count(), counts_.size());
    680 }
    681 
    682 
    683 void Histogram::SampleSet::Accumulate(Sample value,  Count count,
    684                                       size_t index) {
    685   DCHECK(count == 1 || count == -1);
    686   counts_[index] += count;
    687   sum_ += count * value;
    688   redundant_count_ += count;
    689   DCHECK_GE(counts_[index], 0);
    690   DCHECK_GE(sum_, 0);
    691   DCHECK_GE(redundant_count_, 0);
    692 }
    693 
    694 Count Histogram::SampleSet::TotalCount() const {
    695   Count total = 0;
    696   for (Counts::const_iterator it = counts_.begin();
    697        it != counts_.end();
    698        ++it) {
    699     total += *it;
    700   }
    701   return total;
    702 }
    703 
    704 void Histogram::SampleSet::Add(const SampleSet& other) {
    705   DCHECK_EQ(counts_.size(), other.counts_.size());
    706   sum_ += other.sum_;
    707   redundant_count_ += other.redundant_count_;
    708   for (size_t index = 0; index < counts_.size(); ++index)
    709     counts_[index] += other.counts_[index];
    710 }
    711 
    712 void Histogram::SampleSet::Subtract(const SampleSet& other) {
    713   DCHECK_EQ(counts_.size(), other.counts_.size());
    714   // Note: Race conditions in snapshotting a sum may lead to (temporary)
    715   // negative values when snapshots are later combined (and deltas calculated).
    716   // As a result, we don't currently CHCEK() for positive values.
    717   sum_ -= other.sum_;
    718   redundant_count_ -= other.redundant_count_;
    719   for (size_t index = 0; index < counts_.size(); ++index) {
    720     counts_[index] -= other.counts_[index];
    721     DCHECK_GE(counts_[index], 0);
    722   }
    723 }
    724 
    725 bool Histogram::SampleSet::Serialize(Pickle* pickle) const {
    726   pickle->WriteInt64(sum_);
    727   pickle->WriteInt64(redundant_count_);
    728   pickle->WriteSize(counts_.size());
    729 
    730   for (size_t index = 0; index < counts_.size(); ++index) {
    731     pickle->WriteInt(counts_[index]);
    732   }
    733 
    734   return true;
    735 }
    736 
    737 bool Histogram::SampleSet::Deserialize(void** iter, const Pickle& pickle) {
    738   DCHECK_EQ(counts_.size(), 0u);
    739   DCHECK_EQ(sum_, 0);
    740   DCHECK_EQ(redundant_count_, 0);
    741 
    742   size_t counts_size;
    743 
    744   if (!pickle.ReadInt64(iter, &sum_) ||
    745       !pickle.ReadInt64(iter, &redundant_count_) ||
    746       !pickle.ReadSize(iter, &counts_size)) {
    747     return false;
    748   }
    749 
    750   if (counts_size == 0)
    751     return false;
    752 
    753   int count = 0;
    754   for (size_t index = 0; index < counts_size; ++index) {
    755     int i;
    756     if (!pickle.ReadInt(iter, &i))
    757       return false;
    758     counts_.push_back(i);
    759     count += i;
    760   }
    761   DCHECK_EQ(count, redundant_count_);
    762   return count == redundant_count_;
    763 }
    764 
    765 //------------------------------------------------------------------------------
    766 // LinearHistogram: This histogram uses a traditional set of evenly spaced
    767 // buckets.
    768 //------------------------------------------------------------------------------
    769 
    770 LinearHistogram::~LinearHistogram() {
    771 }
    772 
    773 Histogram* LinearHistogram::FactoryGet(const std::string& name,
    774                                        Sample minimum,
    775                                        Sample maximum,
    776                                        size_t bucket_count,
    777                                        Flags flags) {
    778   Histogram* histogram(NULL);
    779 
    780   if (minimum < 1)
    781     minimum = 1;
    782   if (maximum > kSampleType_MAX - 1)
    783     maximum = kSampleType_MAX - 1;
    784 
    785   if (!StatisticsRecorder::FindHistogram(name, &histogram)) {
    786     // To avoid racy destruction at shutdown, the following will be leaked.
    787     LinearHistogram* tentative_histogram =
    788         new LinearHistogram(name, minimum, maximum, bucket_count);
    789     tentative_histogram->InitializeBucketRange();
    790     tentative_histogram->SetFlags(flags);
    791     histogram =
    792         StatisticsRecorder::RegisterOrDeleteDuplicate(tentative_histogram);
    793   }
    794 
    795   DCHECK_EQ(LINEAR_HISTOGRAM, histogram->histogram_type());
    796   DCHECK(histogram->HasConstructorArguments(minimum, maximum, bucket_count));
    797   return histogram;
    798 }
    799 
    800 Histogram* LinearHistogram::FactoryTimeGet(const std::string& name,
    801                                            TimeDelta minimum,
    802                                            TimeDelta maximum,
    803                                            size_t bucket_count,
    804                                            Flags flags) {
    805   return FactoryGet(name, minimum.InMilliseconds(), maximum.InMilliseconds(),
    806                     bucket_count, flags);
    807 }
    808 
    809 Histogram::ClassType LinearHistogram::histogram_type() const {
    810   return LINEAR_HISTOGRAM;
    811 }
    812 
    813 void LinearHistogram::SetRangeDescriptions(
    814     const DescriptionPair descriptions[]) {
    815   for (int i =0; descriptions[i].description; ++i) {
    816     bucket_description_[descriptions[i].sample] = descriptions[i].description;
    817   }
    818 }
    819 
    820 LinearHistogram::LinearHistogram(const std::string& name,
    821                                  Sample minimum,
    822                                  Sample maximum,
    823                                  size_t bucket_count)
    824     : Histogram(name, minimum >= 1 ? minimum : 1, maximum, bucket_count) {
    825 }
    826 
    827 LinearHistogram::LinearHistogram(const std::string& name,
    828                                  TimeDelta minimum,
    829                                  TimeDelta maximum,
    830                                  size_t bucket_count)
    831     : Histogram(name, minimum >= TimeDelta::FromMilliseconds(1) ?
    832                                  minimum : TimeDelta::FromMilliseconds(1),
    833                 maximum, bucket_count) {
    834 }
    835 
    836 void LinearHistogram::InitializeBucketRange() {
    837   DCHECK_GT(declared_min(), 0);  // 0 is the underflow bucket here.
    838   double min = declared_min();
    839   double max = declared_max();
    840   size_t i;
    841   for (i = 1; i < bucket_count(); ++i) {
    842     double linear_range = (min * (bucket_count() -1 - i) + max * (i - 1)) /
    843                           (bucket_count() - 2);
    844     SetBucketRange(i, static_cast<int> (linear_range + 0.5));
    845   }
    846   ResetRangeChecksum();
    847 }
    848 
    849 double LinearHistogram::GetBucketSize(Count current, size_t i) const {
    850   DCHECK_GT(ranges(i + 1), ranges(i));
    851   // Adjacent buckets with different widths would have "surprisingly" many (few)
    852   // samples in a histogram if we didn't normalize this way.
    853   double denominator = ranges(i + 1) - ranges(i);
    854   return current/denominator;
    855 }
    856 
    857 const std::string LinearHistogram::GetAsciiBucketRange(size_t i) const {
    858   int range = ranges(i);
    859   BucketDescriptionMap::const_iterator it = bucket_description_.find(range);
    860   if (it == bucket_description_.end())
    861     return Histogram::GetAsciiBucketRange(i);
    862   return it->second;
    863 }
    864 
    865 bool LinearHistogram::PrintEmptyBucket(size_t index) const {
    866   return bucket_description_.find(ranges(index)) == bucket_description_.end();
    867 }
    868 
    869 
    870 //------------------------------------------------------------------------------
    871 // This section provides implementation for BooleanHistogram.
    872 //------------------------------------------------------------------------------
    873 
    874 Histogram* BooleanHistogram::FactoryGet(const std::string& name, Flags flags) {
    875   Histogram* histogram(NULL);
    876 
    877   if (!StatisticsRecorder::FindHistogram(name, &histogram)) {
    878     // To avoid racy destruction at shutdown, the following will be leaked.
    879     BooleanHistogram* tentative_histogram = new BooleanHistogram(name);
    880     tentative_histogram->InitializeBucketRange();
    881     tentative_histogram->SetFlags(flags);
    882     histogram =
    883         StatisticsRecorder::RegisterOrDeleteDuplicate(tentative_histogram);
    884   }
    885 
    886   DCHECK_EQ(BOOLEAN_HISTOGRAM, histogram->histogram_type());
    887   return histogram;
    888 }
    889 
    890 Histogram::ClassType BooleanHistogram::histogram_type() const {
    891   return BOOLEAN_HISTOGRAM;
    892 }
    893 
    894 void BooleanHistogram::AddBoolean(bool value) {
    895   Add(value ? 1 : 0);
    896 }
    897 
    898 BooleanHistogram::BooleanHistogram(const std::string& name)
    899     : LinearHistogram(name, 1, 2, 3) {
    900 }
    901 
    902 //------------------------------------------------------------------------------
    903 // CustomHistogram:
    904 //------------------------------------------------------------------------------
    905 
    906 Histogram* CustomHistogram::FactoryGet(const std::string& name,
    907                                        const std::vector<Sample>& custom_ranges,
    908                                        Flags flags) {
    909   Histogram* histogram(NULL);
    910 
    911   // Remove the duplicates in the custom ranges array.
    912   std::vector<int> ranges = custom_ranges;
    913   ranges.push_back(0);  // Ensure we have a zero value.
    914   std::sort(ranges.begin(), ranges.end());
    915   ranges.erase(std::unique(ranges.begin(), ranges.end()), ranges.end());
    916   if (ranges.size() <= 1) {
    917     DCHECK(false);
    918     // Note that we pushed a 0 in above, so for defensive code....
    919     ranges.push_back(1);  // Put in some data so we can index to [1].
    920   }
    921 
    922   DCHECK_LT(ranges.back(), kSampleType_MAX);
    923 
    924   if (!StatisticsRecorder::FindHistogram(name, &histogram)) {
    925     // To avoid racy destruction at shutdown, the following will be leaked.
    926     CustomHistogram* tentative_histogram = new CustomHistogram(name, ranges);
    927     tentative_histogram->InitializedCustomBucketRange(ranges);
    928     tentative_histogram->SetFlags(flags);
    929     histogram =
    930         StatisticsRecorder::RegisterOrDeleteDuplicate(tentative_histogram);
    931   }
    932 
    933   DCHECK_EQ(histogram->histogram_type(), CUSTOM_HISTOGRAM);
    934   DCHECK(histogram->HasConstructorArguments(ranges[1], ranges.back(),
    935                                             ranges.size()));
    936   return histogram;
    937 }
    938 
    939 Histogram::ClassType CustomHistogram::histogram_type() const {
    940   return CUSTOM_HISTOGRAM;
    941 }
    942 
    943 CustomHistogram::CustomHistogram(const std::string& name,
    944                                  const std::vector<Sample>& custom_ranges)
    945     : Histogram(name, custom_ranges[1], custom_ranges.back(),
    946                 custom_ranges.size()) {
    947   DCHECK_GT(custom_ranges.size(), 1u);
    948   DCHECK_EQ(custom_ranges[0], 0);
    949 }
    950 
    951 void CustomHistogram::InitializedCustomBucketRange(
    952     const std::vector<Sample>& custom_ranges) {
    953   DCHECK_GT(custom_ranges.size(), 1u);
    954   DCHECK_EQ(custom_ranges[0], 0);
    955   DCHECK_LE(custom_ranges.size(), bucket_count());
    956   for (size_t index = 0; index < custom_ranges.size(); ++index)
    957     SetBucketRange(index, custom_ranges[index]);
    958   ResetRangeChecksum();
    959 }
    960 
    961 double CustomHistogram::GetBucketSize(Count current, size_t i) const {
    962   return 1;
    963 }
    964 
    965 //------------------------------------------------------------------------------
    966 // The next section handles global (central) support for all histograms, as well
    967 // as startup/teardown of this service.
    968 //------------------------------------------------------------------------------
    969 
    970 // This singleton instance should be started during the single threaded portion
    971 // of main(), and hence it is not thread safe.  It initializes globals to
    972 // provide support for all future calls.
    973 StatisticsRecorder::StatisticsRecorder() {
    974   DCHECK(!histograms_);
    975   if (lock_ == NULL) {
    976     // This will leak on purpose. It's the only way to make sure we won't race
    977     // against the static uninitialization of the module while one of our
    978     // static methods relying on the lock get called at an inappropriate time
    979     // during the termination phase. Since it's a static data member, we will
    980     // leak one per process, which would be similar to the instance allocated
    981     // during static initialization and released only on  process termination.
    982     lock_ = new base::Lock;
    983   }
    984   base::AutoLock auto_lock(*lock_);
    985   histograms_ = new HistogramMap;
    986 }
    987 
    988 StatisticsRecorder::~StatisticsRecorder() {
    989   DCHECK(histograms_ && lock_);
    990 
    991   if (dump_on_exit_) {
    992     std::string output;
    993     WriteGraph("", &output);
    994     LOG(INFO) << output;
    995   }
    996   // Clean up.
    997   HistogramMap* histograms = NULL;
    998   {
    999     base::AutoLock auto_lock(*lock_);
   1000     histograms = histograms_;
   1001     histograms_ = NULL;
   1002   }
   1003   delete histograms;
   1004   // We don't delete lock_ on purpose to avoid having to properly protect
   1005   // against it going away after we checked for NULL in the static methods.
   1006 }
   1007 
   1008 // static
   1009 bool StatisticsRecorder::IsActive() {
   1010   if (lock_ == NULL)
   1011     return false;
   1012   base::AutoLock auto_lock(*lock_);
   1013   return NULL != histograms_;
   1014 }
   1015 
   1016 Histogram* StatisticsRecorder::RegisterOrDeleteDuplicate(Histogram* histogram) {
   1017   DCHECK(histogram->HasValidRangeChecksum());
   1018   if (lock_ == NULL)
   1019     return histogram;
   1020   base::AutoLock auto_lock(*lock_);
   1021   if (!histograms_)
   1022     return histogram;
   1023   const std::string name = histogram->histogram_name();
   1024   HistogramMap::iterator it = histograms_->find(name);
   1025   // Avoid overwriting a previous registration.
   1026   if (histograms_->end() == it) {
   1027     (*histograms_)[name] = histogram;
   1028   } else {
   1029     delete histogram;  // We already have one by this name.
   1030     histogram = it->second;
   1031   }
   1032   return histogram;
   1033 }
   1034 
   1035 // static
   1036 void StatisticsRecorder::WriteHTMLGraph(const std::string& query,
   1037                                         std::string* output) {
   1038   if (!IsActive())
   1039     return;
   1040   output->append("<html><head><title>About Histograms");
   1041   if (!query.empty())
   1042     output->append(" - " + query);
   1043   output->append("</title>"
   1044                  // We'd like the following no-cache... but it doesn't work.
   1045                  // "<META HTTP-EQUIV=\"Pragma\" CONTENT=\"no-cache\">"
   1046                  "</head><body>");
   1047 
   1048   Histograms snapshot;
   1049   GetSnapshot(query, &snapshot);
   1050   for (Histograms::iterator it = snapshot.begin();
   1051        it != snapshot.end();
   1052        ++it) {
   1053     (*it)->WriteHTMLGraph(output);
   1054     output->append("<br><hr><br>");
   1055   }
   1056   output->append("</body></html>");
   1057 }
   1058 
   1059 // static
   1060 void StatisticsRecorder::WriteGraph(const std::string& query,
   1061                                     std::string* output) {
   1062   if (!IsActive())
   1063     return;
   1064   if (query.length())
   1065     StringAppendF(output, "Collections of histograms for %s\n", query.c_str());
   1066   else
   1067     output->append("Collections of all histograms\n");
   1068 
   1069   Histograms snapshot;
   1070   GetSnapshot(query, &snapshot);
   1071   for (Histograms::iterator it = snapshot.begin();
   1072        it != snapshot.end();
   1073        ++it) {
   1074     (*it)->WriteAscii(true, "\n", output);
   1075     output->append("\n");
   1076   }
   1077 }
   1078 
   1079 // static
   1080 void StatisticsRecorder::GetHistograms(Histograms* output) {
   1081   if (lock_ == NULL)
   1082     return;
   1083   base::AutoLock auto_lock(*lock_);
   1084   if (!histograms_)
   1085     return;
   1086   for (HistogramMap::iterator it = histograms_->begin();
   1087        histograms_->end() != it;
   1088        ++it) {
   1089     DCHECK_EQ(it->first, it->second->histogram_name());
   1090     output->push_back(it->second);
   1091   }
   1092 }
   1093 
   1094 bool StatisticsRecorder::FindHistogram(const std::string& name,
   1095                                        Histogram** histogram) {
   1096   if (lock_ == NULL)
   1097     return false;
   1098   base::AutoLock auto_lock(*lock_);
   1099   if (!histograms_)
   1100     return false;
   1101   HistogramMap::iterator it = histograms_->find(name);
   1102   if (histograms_->end() == it)
   1103     return false;
   1104   *histogram = it->second;
   1105   return true;
   1106 }
   1107 
   1108 // private static
   1109 void StatisticsRecorder::GetSnapshot(const std::string& query,
   1110                                      Histograms* snapshot) {
   1111   if (lock_ == NULL)
   1112     return;
   1113   base::AutoLock auto_lock(*lock_);
   1114   if (!histograms_)
   1115     return;
   1116   for (HistogramMap::iterator it = histograms_->begin();
   1117        histograms_->end() != it;
   1118        ++it) {
   1119     if (it->first.find(query) != std::string::npos)
   1120       snapshot->push_back(it->second);
   1121   }
   1122 }
   1123 
   1124 // static
   1125 StatisticsRecorder::HistogramMap* StatisticsRecorder::histograms_ = NULL;
   1126 // static
   1127 base::Lock* StatisticsRecorder::lock_ = NULL;
   1128 // static
   1129 bool StatisticsRecorder::dump_on_exit_ = false;
   1130 
   1131 }  // namespace base
   1132