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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 "base/memory/scoped_ptr.h"
      8 #include "base/metrics/histogram_flattener.h"
      9 #include "base/metrics/histogram_samples.h"
     10 #include "base/metrics/statistics_recorder.h"
     11 #include "base/stl_util.h"
     12 
     13 using std::map;
     14 using std::string;
     15 
     16 namespace base {
     17 
     18 HistogramSnapshotManager::HistogramSnapshotManager(
     19     HistogramFlattener* histogram_flattener)
     20     : histogram_flattener_(histogram_flattener) {
     21   DCHECK(histogram_flattener_);
     22 }
     23 
     24 HistogramSnapshotManager::~HistogramSnapshotManager() {
     25   STLDeleteValues(&logged_samples_);
     26 }
     27 
     28 void HistogramSnapshotManager::PrepareDeltas(HistogramBase::Flags flag_to_set,
     29                                              bool record_only_uma) {
     30   StatisticsRecorder::Histograms histograms;
     31   StatisticsRecorder::GetHistograms(&histograms);
     32   for (StatisticsRecorder::Histograms::const_iterator it = histograms.begin();
     33        histograms.end() != it;
     34        ++it) {
     35     (*it)->SetFlags(flag_to_set);
     36     if (record_only_uma &&
     37         0 == ((*it)->flags() & Histogram::kUmaTargetedHistogramFlag))
     38       continue;
     39     PrepareDelta(**it);
     40   }
     41 }
     42 
     43 void HistogramSnapshotManager::PrepareDelta(const HistogramBase& histogram) {
     44   DCHECK(histogram_flattener_);
     45 
     46   // Get up-to-date snapshot of sample stats.
     47   scoped_ptr<HistogramSamples> snapshot(histogram.SnapshotSamples());
     48   const std::string& histogram_name = histogram.histogram_name();
     49 
     50   int corruption = histogram.FindCorruption(*snapshot);
     51 
     52   // Crash if we detect that our histograms have been overwritten.  This may be
     53   // a fair distance from the memory smasher, but we hope to correlate these
     54   // crashes with other events, such as plugins, or usage patterns, etc.
     55   if (HistogramBase::BUCKET_ORDER_ERROR & corruption) {
     56     // The checksum should have caught this, so crash separately if it didn't.
     57     CHECK_NE(0, HistogramBase::RANGE_CHECKSUM_ERROR & corruption);
     58     CHECK(false);  // Crash for the bucket order corruption.
     59   }
     60   // Checksum corruption might not have caused order corruption.
     61   CHECK_EQ(0, HistogramBase::RANGE_CHECKSUM_ERROR & corruption);
     62 
     63   // Note, at this point corruption can only be COUNT_HIGH_ERROR or
     64   // COUNT_LOW_ERROR and they never arise together, so we don't need to extract
     65   // bits from corruption.
     66   if (corruption) {
     67     DLOG(ERROR) << "Histogram: " << histogram_name
     68                 << " has data corruption: " << corruption;
     69     histogram_flattener_->InconsistencyDetected(
     70         static_cast<HistogramBase::Inconsistency>(corruption));
     71     // Don't record corrupt data to metrics services.
     72     int old_corruption = inconsistencies_[histogram_name];
     73     if (old_corruption == (corruption | old_corruption))
     74       return;  // We've already seen this corruption for this histogram.
     75     inconsistencies_[histogram_name] |= corruption;
     76     histogram_flattener_->UniqueInconsistencyDetected(
     77         static_cast<HistogramBase::Inconsistency>(corruption));
     78     return;
     79   }
     80 
     81   HistogramSamples* to_log;
     82   map<string, HistogramSamples*>::iterator it =
     83       logged_samples_.find(histogram_name);
     84   if (it == logged_samples_.end()) {
     85     to_log = snapshot.release();
     86 
     87     // This histogram has not been logged before, add a new entry.
     88     logged_samples_[histogram_name] = to_log;
     89   } else {
     90     HistogramSamples* already_logged = it->second;
     91     InspectLoggedSamplesInconsistency(*snapshot, already_logged);
     92     snapshot->Subtract(*already_logged);
     93     already_logged->Add(*snapshot);
     94     to_log = snapshot.get();
     95   }
     96 
     97   if (to_log->redundant_count() > 0)
     98     histogram_flattener_->RecordDelta(histogram, *to_log);
     99 }
    100 
    101 void HistogramSnapshotManager::InspectLoggedSamplesInconsistency(
    102       const HistogramSamples& new_snapshot,
    103       HistogramSamples* logged_samples) {
    104   HistogramBase::Count discrepancy =
    105       logged_samples->TotalCount() - logged_samples->redundant_count();
    106   if (!discrepancy)
    107     return;
    108 
    109   histogram_flattener_->InconsistencyDetectedInLoggedCount(discrepancy);
    110   if (discrepancy > Histogram::kCommonRaceBasedCountMismatch) {
    111     // Fix logged_samples.
    112     logged_samples->Subtract(*logged_samples);
    113     logged_samples->Add(new_snapshot);
    114   }
    115 }
    116 
    117 }  // namespace base
    118