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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 namespace base {
     14 
     15 HistogramSnapshotManager::HistogramSnapshotManager(
     16     HistogramFlattener* histogram_flattener)
     17     : histogram_flattener_(histogram_flattener) {
     18   DCHECK(histogram_flattener_);
     19 }
     20 
     21 HistogramSnapshotManager::~HistogramSnapshotManager() {
     22   STLDeleteValues(&logged_samples_);
     23 }
     24 
     25 void HistogramSnapshotManager::PrepareDeltas(
     26     HistogramBase::Flags flag_to_set,
     27     HistogramBase::Flags required_flags) {
     28   StatisticsRecorder::Histograms histograms;
     29   StatisticsRecorder::GetHistograms(&histograms);
     30   for (StatisticsRecorder::Histograms::const_iterator it = histograms.begin();
     31        histograms.end() != it;
     32        ++it) {
     33     (*it)->SetFlags(flag_to_set);
     34     if (((*it)->flags() & required_flags) == required_flags)
     35       PrepareDelta(**it);
     36   }
     37 }
     38 
     39 void HistogramSnapshotManager::PrepareDelta(const HistogramBase& histogram) {
     40   DCHECK(histogram_flattener_);
     41 
     42   // Get up-to-date snapshot of sample stats.
     43   scoped_ptr<HistogramSamples> snapshot(histogram.SnapshotSamples());
     44 
     45   // Crash if we detect that our histograms have been overwritten.  This may be
     46   // a fair distance from the memory smasher, but we hope to correlate these
     47   // crashes with other events, such as plugins, or usage patterns, etc.
     48   int corruption = histogram.FindCorruption(*snapshot);
     49   if (HistogramBase::BUCKET_ORDER_ERROR & corruption) {
     50     // The checksum should have caught this, so crash separately if it didn't.
     51     CHECK_NE(0, HistogramBase::RANGE_CHECKSUM_ERROR & corruption);
     52     CHECK(false);  // Crash for the bucket order corruption.
     53   }
     54   // Checksum corruption might not have caused order corruption.
     55   CHECK_EQ(0, HistogramBase::RANGE_CHECKSUM_ERROR & corruption);
     56 
     57   // Note, at this point corruption can only be COUNT_HIGH_ERROR or
     58   // COUNT_LOW_ERROR and they never arise together, so we don't need to extract
     59   // bits from corruption.
     60   const uint64_t histogram_hash = histogram.name_hash();
     61   if (corruption) {
     62     DLOG(ERROR) << "Histogram: " << histogram.histogram_name()
     63                 << " has data corruption: " << corruption;
     64     histogram_flattener_->InconsistencyDetected(
     65         static_cast<HistogramBase::Inconsistency>(corruption));
     66     // Don't record corrupt data to metrics services.
     67     int old_corruption = inconsistencies_[histogram_hash];
     68     if (old_corruption == (corruption | old_corruption))
     69       return;  // We've already seen this corruption for this histogram.
     70     inconsistencies_[histogram_hash] |= corruption;
     71     histogram_flattener_->UniqueInconsistencyDetected(
     72         static_cast<HistogramBase::Inconsistency>(corruption));
     73     return;
     74   }
     75 
     76   HistogramSamples* to_log;
     77   auto it = logged_samples_.find(histogram_hash);
     78   if (it == logged_samples_.end()) {
     79     to_log = snapshot.release();
     80 
     81     // This histogram has not been logged before, add a new entry.
     82     logged_samples_[histogram_hash] = to_log;
     83   } else {
     84     HistogramSamples* already_logged = it->second;
     85     InspectLoggedSamplesInconsistency(*snapshot, already_logged);
     86     snapshot->Subtract(*already_logged);
     87     already_logged->Add(*snapshot);
     88     to_log = snapshot.get();
     89   }
     90 
     91   if (to_log->TotalCount() > 0)
     92     histogram_flattener_->RecordDelta(histogram, *to_log);
     93 }
     94 
     95 void HistogramSnapshotManager::InspectLoggedSamplesInconsistency(
     96       const HistogramSamples& new_snapshot,
     97       HistogramSamples* logged_samples) {
     98   HistogramBase::Count discrepancy =
     99       logged_samples->TotalCount() - logged_samples->redundant_count();
    100   if (!discrepancy)
    101     return;
    102 
    103   histogram_flattener_->InconsistencyDetectedInLoggedCount(discrepancy);
    104   if (discrepancy > Histogram::kCommonRaceBasedCountMismatch) {
    105     // Fix logged_samples.
    106     logged_samples->Subtract(*logged_samples);
    107     logged_samples->Add(new_snapshot);
    108   }
    109 }
    110 
    111 }  // namespace base
    112