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