histogram.cc revision ddb351dbec246cf1fab5ec20d2d5520909041de1 
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
22namespace base {
23
24// Static table of checksums for all possible 8 bit bytes.
25const uint32 Histogram::kCrcTable[256] = {0x0, 0x77073096L, 0xee0e612cL,
260x990951baL, 0x76dc419L, 0x706af48fL, 0xe963a535L, 0x9e6495a3L, 0xedb8832L,
270x79dcb8a4L, 0xe0d5e91eL, 0x97d2d988L, 0x9b64c2bL, 0x7eb17cbdL, 0xe7b82d07L,
280x90bf1d91L, 0x1db71064L, 0x6ab020f2L, 0xf3b97148L, 0x84be41deL, 0x1adad47dL,
290x6ddde4ebL, 0xf4d4b551L, 0x83d385c7L, 0x136c9856L, 0x646ba8c0L, 0xfd62f97aL,
300x8a65c9ecL, 0x14015c4fL, 0x63066cd9L, 0xfa0f3d63L, 0x8d080df5L, 0x3b6e20c8L,
310x4c69105eL, 0xd56041e4L, 0xa2677172L, 0x3c03e4d1L, 0x4b04d447L, 0xd20d85fdL,
320xa50ab56bL, 0x35b5a8faL, 0x42b2986cL, 0xdbbbc9d6L, 0xacbcf940L, 0x32d86ce3L,
330x45df5c75L, 0xdcd60dcfL, 0xabd13d59L, 0x26d930acL, 0x51de003aL, 0xc8d75180L,
340xbfd06116L, 0x21b4f4b5L, 0x56b3c423L, 0xcfba9599L, 0xb8bda50fL, 0x2802b89eL,
350x5f058808L, 0xc60cd9b2L, 0xb10be924L, 0x2f6f7c87L, 0x58684c11L, 0xc1611dabL,
360xb6662d3dL, 0x76dc4190L, 0x1db7106L, 0x98d220bcL, 0xefd5102aL, 0x71b18589L,
370x6b6b51fL, 0x9fbfe4a5L, 0xe8b8d433L, 0x7807c9a2L, 0xf00f934L, 0x9609a88eL,
380xe10e9818L, 0x7f6a0dbbL, 0x86d3d2dL, 0x91646c97L, 0xe6635c01L, 0x6b6b51f4L,
390x1c6c6162L, 0x856530d8L, 0xf262004eL, 0x6c0695edL, 0x1b01a57bL, 0x8208f4c1L,
400xf50fc457L, 0x65b0d9c6L, 0x12b7e950L, 0x8bbeb8eaL, 0xfcb9887cL, 0x62dd1ddfL,
410x15da2d49L, 0x8cd37cf3L, 0xfbd44c65L, 0x4db26158L, 0x3ab551ceL, 0xa3bc0074L,
420xd4bb30e2L, 0x4adfa541L, 0x3dd895d7L, 0xa4d1c46dL, 0xd3d6f4fbL, 0x4369e96aL,
430x346ed9fcL, 0xad678846L, 0xda60b8d0L, 0x44042d73L, 0x33031de5L, 0xaa0a4c5fL,
440xdd0d7cc9L, 0x5005713cL, 0x270241aaL, 0xbe0b1010L, 0xc90c2086L, 0x5768b525L,
450x206f85b3L, 0xb966d409L, 0xce61e49fL, 0x5edef90eL, 0x29d9c998L, 0xb0d09822L,
460xc7d7a8b4L, 0x59b33d17L, 0x2eb40d81L, 0xb7bd5c3bL, 0xc0ba6cadL, 0xedb88320L,
470x9abfb3b6L, 0x3b6e20cL, 0x74b1d29aL, 0xead54739L, 0x9dd277afL, 0x4db2615L,
480x73dc1683L, 0xe3630b12L, 0x94643b84L, 0xd6d6a3eL, 0x7a6a5aa8L, 0xe40ecf0bL,
490x9309ff9dL, 0xa00ae27L, 0x7d079eb1L, 0xf00f9344L, 0x8708a3d2L, 0x1e01f268L,
500x6906c2feL, 0xf762575dL, 0x806567cbL, 0x196c3671L, 0x6e6b06e7L, 0xfed41b76L,
510x89d32be0L, 0x10da7a5aL, 0x67dd4accL, 0xf9b9df6fL, 0x8ebeeff9L, 0x17b7be43L,
520x60b08ed5L, 0xd6d6a3e8L, 0xa1d1937eL, 0x38d8c2c4L, 0x4fdff252L, 0xd1bb67f1L,
530xa6bc5767L, 0x3fb506ddL, 0x48b2364bL, 0xd80d2bdaL, 0xaf0a1b4cL, 0x36034af6L,
540x41047a60L, 0xdf60efc3L, 0xa867df55L, 0x316e8eefL, 0x4669be79L, 0xcb61b38cL,
550xbc66831aL, 0x256fd2a0L, 0x5268e236L, 0xcc0c7795L, 0xbb0b4703L, 0x220216b9L,
560x5505262fL, 0xc5ba3bbeL, 0xb2bd0b28L, 0x2bb45a92L, 0x5cb36a04L, 0xc2d7ffa7L,
570xb5d0cf31L, 0x2cd99e8bL, 0x5bdeae1dL, 0x9b64c2b0L, 0xec63f226L, 0x756aa39cL,
580x26d930aL, 0x9c0906a9L, 0xeb0e363fL, 0x72076785L, 0x5005713L, 0x95bf4a82L,
590xe2b87a14L, 0x7bb12baeL, 0xcb61b38L, 0x92d28e9bL, 0xe5d5be0dL, 0x7cdcefb7L,
600xbdbdf21L, 0x86d3d2d4L, 0xf1d4e242L, 0x68ddb3f8L, 0x1fda836eL, 0x81be16cdL,
610xf6b9265bL, 0x6fb077e1L, 0x18b74777L, 0x88085ae6L, 0xff0f6a70L, 0x66063bcaL,
620x11010b5cL, 0x8f659effL, 0xf862ae69L, 0x616bffd3L, 0x166ccf45L, 0xa00ae278L,
630xd70dd2eeL, 0x4e048354L, 0x3903b3c2L, 0xa7672661L, 0xd06016f7L, 0x4969474dL,
640x3e6e77dbL, 0xaed16a4aL, 0xd9d65adcL, 0x40df0b66L, 0x37d83bf0L, 0xa9bcae53L,
650xdebb9ec5L, 0x47b2cf7fL, 0x30b5ffe9L, 0xbdbdf21cL, 0xcabac28aL, 0x53b39330L,
660x24b4a3a6L, 0xbad03605L, 0xcdd70693L, 0x54de5729L, 0x23d967bfL, 0xb3667a2eL,
670xc4614ab8L, 0x5d681b02L, 0x2a6f2b94L, 0xb40bbe37L, 0xc30c8ea1L, 0x5a05df1bL,
680x2d02ef8dL,
69};
70
71typedef Histogram::Count Count;
72
73// static
74const size_t Histogram::kBucketCount_MAX = 16384u;
75
76Histogram* 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
107Histogram* 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
116void 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
127void Histogram::AddBoolean(bool value) {
128  DCHECK(false);
129}
130
131void Histogram::AddSampleSet(const SampleSet& sample) {
132  sample_.Add(sample);
133}
134
135void Histogram::SetRangeDescriptions(const DescriptionPair descriptions[]) {
136  DCHECK(false);
137}
138
139// The following methods provide a graphical histogram display.
140void 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
147void 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
212std::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
230bool 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
308Histogram::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
352Histogram::ClassType Histogram::histogram_type() const {
353  return HISTOGRAM;
354}
355
356Histogram::Sample Histogram::ranges(size_t i) const {
357  return ranges_[i];
358}
359
360size_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.
366void Histogram::SnapshotSample(SampleSet* sample) const {
367  // Note locking not done in this version!!!
368  *sample = sample_;
369}
370
371bool 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
378bool 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
386bool Histogram::HasValidRangeChecksum() const {
387  return CalculateRangeChecksum() == range_checksum_;
388}
389
390Histogram::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
403Histogram::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
416Histogram::~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.
435void 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
462bool Histogram::PrintEmptyBucket(size_t index) const {
463  return true;
464}
465
466size_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.
496double 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
505void Histogram::ResetRangeChecksum() {
506  range_checksum_ = CalculateRangeChecksum();
507}
508
509const 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.
519void 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
524void Histogram::SetBucketRange(size_t i, Sample value) {
525  DCHECK_GT(bucket_count_, i);
526  ranges_[i] = value;
527}
528
529bool 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
539uint32 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
547void 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.
571uint32 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
601double 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
611void 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
629void 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
642void Histogram::WriteAsciiBucketValue(Count current, double scaled_sum,
643                                      std::string* output) const {
644  StringAppendF(output, " (%d = %3.1f%%)", current, current/scaled_sum);
645}
646
647void 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
665Histogram::SampleSet::SampleSet()
666    : counts_(),
667      sum_(0),
668      redundant_count_(0) {
669}
670
671Histogram::SampleSet::~SampleSet() {
672}
673
674void Histogram::SampleSet::Resize(const Histogram& histogram) {
675  counts_.resize(histogram.bucket_count(), 0);
676}
677
678void Histogram::SampleSet::CheckSize(const Histogram& histogram) const {
679  DCHECK_EQ(histogram.bucket_count(), counts_.size());
680}
681
682
683void 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
694Count 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
704void 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
712void 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
725bool 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
737bool 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
770LinearHistogram::~LinearHistogram() {
771}
772
773Histogram* 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
800Histogram* 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
809Histogram::ClassType LinearHistogram::histogram_type() const {
810  return LINEAR_HISTOGRAM;
811}
812
813void 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
820LinearHistogram::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
827LinearHistogram::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
836void 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
849double 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
857const 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
865bool 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
874Histogram* 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
890Histogram::ClassType BooleanHistogram::histogram_type() const {
891  return BOOLEAN_HISTOGRAM;
892}
893
894void BooleanHistogram::AddBoolean(bool value) {
895  Add(value ? 1 : 0);
896}
897
898BooleanHistogram::BooleanHistogram(const std::string& name)
899    : LinearHistogram(name, 1, 2, 3) {
900}
901
902//------------------------------------------------------------------------------
903// CustomHistogram:
904//------------------------------------------------------------------------------
905
906Histogram* 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
939Histogram::ClassType CustomHistogram::histogram_type() const {
940  return CUSTOM_HISTOGRAM;
941}
942
943CustomHistogram::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
951void 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
961double 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.
973StatisticsRecorder::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
988StatisticsRecorder::~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
1009bool StatisticsRecorder::IsActive() {
1010  if (lock_ == NULL)
1011    return false;
1012  base::AutoLock auto_lock(*lock_);
1013  return NULL != histograms_;
1014}
1015
1016Histogram* 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
1036void 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
1060void 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
1080void 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
1094bool 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
1109void 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
1125StatisticsRecorder::HistogramMap* StatisticsRecorder::histograms_ = NULL;
1126// static
1127base::Lock* StatisticsRecorder::lock_ = NULL;
1128// static
1129bool StatisticsRecorder::dump_on_exit_ = false;
1130
1131}  // namespace base
1132