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      1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #include "base/metrics/histogram_snapshot_manager.h"
      6 
      7 #include <memory>
      8 
      9 #include "base/debug/alias.h"
     10 #include "base/metrics/histogram_flattener.h"
     11 #include "base/metrics/histogram_samples.h"
     12 #include "base/metrics/statistics_recorder.h"
     13 #include "base/stl_util.h"
     14 
     15 namespace base {
     16 
     17 HistogramSnapshotManager::HistogramSnapshotManager(
     18     HistogramFlattener* histogram_flattener)
     19     : histogram_flattener_(histogram_flattener) {
     20   DCHECK(histogram_flattener_);
     21 }
     22 
     23 HistogramSnapshotManager::~HistogramSnapshotManager() {
     24 }
     25 
     26 void HistogramSnapshotManager::PrepareDelta(HistogramBase* histogram) {
     27   PrepareSamples(histogram, histogram->SnapshotDelta());
     28 }
     29 
     30 void HistogramSnapshotManager::PrepareFinalDelta(
     31     const HistogramBase* histogram) {
     32   PrepareSamples(histogram, histogram->SnapshotFinalDelta());
     33 }
     34 
     35 void HistogramSnapshotManager::PrepareSamples(
     36     const HistogramBase* histogram,
     37     std::unique_ptr<HistogramSamples> samples) {
     38   DCHECK(histogram_flattener_);
     39 
     40   // Get information known about this histogram. If it did not previously
     41   // exist, one will be created and initialized.
     42   SampleInfo* sample_info = &known_histograms_[histogram->name_hash()];
     43 
     44   // Crash if we detect that our histograms have been overwritten.  This may be
     45   // a fair distance from the memory smasher, but we hope to correlate these
     46   // crashes with other events, such as plugins, or usage patterns, etc.
     47   uint32_t corruption = histogram->FindCorruption(*samples);
     48   if (HistogramBase::BUCKET_ORDER_ERROR & corruption) {
     49     // Extract fields useful during debug.
     50     const BucketRanges* ranges =
     51         static_cast<const Histogram*>(histogram)->bucket_ranges();
     52     std::vector<HistogramBase::Sample> ranges_copy;
     53     for (size_t i = 0; i < ranges->size(); ++i)
     54       ranges_copy.push_back(ranges->range(i));
     55     HistogramBase::Sample* ranges_ptr = &ranges_copy[0];
     56     uint32_t ranges_checksum = ranges->checksum();
     57     uint32_t ranges_calc_checksum = ranges->CalculateChecksum();
     58     const char* histogram_name = histogram->histogram_name().c_str();
     59     int32_t flags = histogram->flags();
     60     // The checksum should have caught this, so crash separately if it didn't.
     61     CHECK_NE(0U, HistogramBase::RANGE_CHECKSUM_ERROR & corruption);
     62     CHECK(false);  // Crash for the bucket order corruption.
     63     // Ensure that compiler keeps around pointers to |histogram| and its
     64     // internal |bucket_ranges_| for any minidumps.
     65     base::debug::Alias(&ranges_ptr);
     66     base::debug::Alias(&ranges_checksum);
     67     base::debug::Alias(&ranges_calc_checksum);
     68     base::debug::Alias(&histogram_name);
     69     base::debug::Alias(&flags);
     70   }
     71   // Checksum corruption might not have caused order corruption.
     72   CHECK_EQ(0U, HistogramBase::RANGE_CHECKSUM_ERROR & corruption);
     73 
     74   // Note, at this point corruption can only be COUNT_HIGH_ERROR or
     75   // COUNT_LOW_ERROR and they never arise together, so we don't need to extract
     76   // bits from corruption.
     77   if (corruption) {
     78     DLOG(ERROR) << "Histogram: \"" << histogram->histogram_name()
     79                 << "\" has data corruption: " << corruption;
     80     histogram_flattener_->InconsistencyDetected(
     81         static_cast<HistogramBase::Inconsistency>(corruption));
     82     // Don't record corrupt data to metrics services.
     83     const uint32_t old_corruption = sample_info->inconsistencies;
     84     if (old_corruption == (corruption | old_corruption))
     85       return;  // We've already seen this corruption for this histogram.
     86     sample_info->inconsistencies |= corruption;
     87     histogram_flattener_->UniqueInconsistencyDetected(
     88         static_cast<HistogramBase::Inconsistency>(corruption));
     89     return;
     90   }
     91 
     92   if (samples->TotalCount() > 0)
     93     histogram_flattener_->RecordDelta(*histogram, *samples);
     94 }
     95 
     96 void HistogramSnapshotManager::InspectLoggedSamplesInconsistency(
     97       const HistogramSamples& new_snapshot,
     98       HistogramSamples* logged_samples) {
     99   HistogramBase::Count discrepancy =
    100       logged_samples->TotalCount() - logged_samples->redundant_count();
    101   if (!discrepancy)
    102     return;
    103 
    104   histogram_flattener_->InconsistencyDetectedInLoggedCount(discrepancy);
    105   if (discrepancy > Histogram::kCommonRaceBasedCountMismatch) {
    106     // Fix logged_samples.
    107     logged_samples->Subtract(*logged_samples);
    108     logged_samples->Add(new_snapshot);
    109   }
    110 }
    111 
    112 }  // namespace base
    113