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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 namespace {
     18 
     19 // A simple object to set an "active" flag and clear it upon destruction. It is
     20 // an error if the flag is already set.
     21 class MakeActive {
     22  public:
     23   MakeActive(std::atomic<bool>* is_active) : is_active_(is_active) {
     24     bool was_active = is_active_->exchange(true, std::memory_order_relaxed);
     25     CHECK(!was_active);
     26   }
     27   ~MakeActive() { is_active_->store(false, std::memory_order_relaxed); }
     28 
     29  private:
     30   std::atomic<bool>* is_active_;
     31 
     32   DISALLOW_COPY_AND_ASSIGN(MakeActive);
     33 };
     34 
     35 }  // namespace
     36 
     37 HistogramSnapshotManager::HistogramSnapshotManager(
     38     HistogramFlattener* histogram_flattener)
     39     : histogram_flattener_(histogram_flattener) {
     40   DCHECK(histogram_flattener_);
     41   is_active_.store(false, std::memory_order_relaxed);
     42 }
     43 
     44 HistogramSnapshotManager::~HistogramSnapshotManager() = default;
     45 
     46 void HistogramSnapshotManager::PrepareDeltas(
     47     const std::vector<HistogramBase*>& histograms,
     48     HistogramBase::Flags flags_to_set,
     49     HistogramBase::Flags required_flags) {
     50   for (HistogramBase* const histogram : histograms) {
     51     histogram->SetFlags(flags_to_set);
     52     if ((histogram->flags() & required_flags) == required_flags)
     53       PrepareDelta(histogram);
     54   }
     55 }
     56 
     57 void HistogramSnapshotManager::PrepareDelta(HistogramBase* histogram) {
     58   histogram->ValidateHistogramContents();
     59   PrepareSamples(histogram, histogram->SnapshotDelta());
     60 }
     61 
     62 void HistogramSnapshotManager::PrepareFinalDelta(
     63     const HistogramBase* histogram) {
     64   histogram->ValidateHistogramContents();
     65   PrepareSamples(histogram, histogram->SnapshotFinalDelta());
     66 }
     67 
     68 void HistogramSnapshotManager::PrepareSamples(
     69     const HistogramBase* histogram,
     70     std::unique_ptr<HistogramSamples> samples) {
     71   DCHECK(histogram_flattener_);
     72 
     73   // Ensure that there is no concurrent access going on while accessing the
     74   // set of known histograms. The flag will be reset when this object goes
     75   // out of scope.
     76   MakeActive make_active(&is_active_);
     77 
     78   // Get information known about this histogram. If it did not previously
     79   // exist, one will be created and initialized.
     80   SampleInfo* sample_info = &known_histograms_[histogram->name_hash()];
     81 
     82   // Crash if we detect that our histograms have been overwritten.  This may be
     83   // a fair distance from the memory smasher, but we hope to correlate these
     84   // crashes with other events, such as plugins, or usage patterns, etc.
     85   uint32_t corruption = histogram->FindCorruption(*samples);
     86   if (HistogramBase::BUCKET_ORDER_ERROR & corruption) {
     87     // Extract fields useful during debug.
     88     const BucketRanges* ranges =
     89         static_cast<const Histogram*>(histogram)->bucket_ranges();
     90     uint32_t ranges_checksum = ranges->checksum();
     91     uint32_t ranges_calc_checksum = ranges->CalculateChecksum();
     92     int32_t flags = histogram->flags();
     93     // The checksum should have caught this, so crash separately if it didn't.
     94     CHECK_NE(0U, HistogramBase::RANGE_CHECKSUM_ERROR & corruption);
     95     CHECK(false);  // Crash for the bucket order corruption.
     96     // Ensure that compiler keeps around pointers to |histogram| and its
     97     // internal |bucket_ranges_| for any minidumps.
     98     base::debug::Alias(&ranges_checksum);
     99     base::debug::Alias(&ranges_calc_checksum);
    100     base::debug::Alias(&flags);
    101   }
    102   // Checksum corruption might not have caused order corruption.
    103   CHECK_EQ(0U, HistogramBase::RANGE_CHECKSUM_ERROR & corruption);
    104 
    105   // Note, at this point corruption can only be COUNT_HIGH_ERROR or
    106   // COUNT_LOW_ERROR and they never arise together, so we don't need to extract
    107   // bits from corruption.
    108   if (corruption) {
    109     DLOG(ERROR) << "Histogram: \"" << histogram->histogram_name()
    110                 << "\" has data corruption: " << corruption;
    111     // Don't record corrupt data to metrics services.
    112     const uint32_t old_corruption = sample_info->inconsistencies;
    113     if (old_corruption == (corruption | old_corruption))
    114       return;  // We've already seen this corruption for this histogram.
    115     sample_info->inconsistencies |= corruption;
    116     return;
    117   }
    118 
    119   if (samples->TotalCount() > 0)
    120     histogram_flattener_->RecordDelta(*histogram, *samples);
    121 }
    122 
    123 }  // namespace base
    124