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:
MakeActive(std::atomic<bool> * is_active)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 }
~MakeActive()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
HistogramSnapshotManager(HistogramFlattener * histogram_flattener)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
PrepareDeltas(const std::vector<HistogramBase * > & histograms,HistogramBase::Flags flags_to_set,HistogramBase::Flags required_flags)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
PrepareDelta(HistogramBase * histogram)57 void HistogramSnapshotManager::PrepareDelta(HistogramBase* histogram) {
58 histogram->ValidateHistogramContents();
59 PrepareSamples(histogram, histogram->SnapshotDelta());
60 }
61
PrepareFinalDelta(const HistogramBase * histogram)62 void HistogramSnapshotManager::PrepareFinalDelta(
63 const HistogramBase* histogram) {
64 histogram->ValidateHistogramContents();
65 PrepareSamples(histogram, histogram->SnapshotFinalDelta());
66 }
67
PrepareSamples(const HistogramBase * histogram,std::unique_ptr<HistogramSamples> samples)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