[histogram] Make histograms more resistant to overflows.

base/metrics/sparse_histogram.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/metrics/sparse_histogram.h"
 
 #include <utility>
 
 #include "base/memory/ptr_util.h"
 #include "base/metrics/metrics_hashes.h"
@@ skipping 67 matching lines @@
     const std::string& name,
     HistogramSamples::Metadata* meta,
     HistogramSamples::Metadata* logged_meta) {
   return WrapUnique(
       new SparseHistogram(allocator, name, meta, logged_meta));
 }
 
 SparseHistogram::~SparseHistogram() {}
 
 uint64_t SparseHistogram::name_hash() const {
-  return samples_->id();
+  return unlogged_samples_->id();
 }
 
 HistogramType SparseHistogram::GetHistogramType() const {
   return SPARSE_HISTOGRAM;
 }
 
 bool SparseHistogram::HasConstructionArguments(
     Sample expected_minimum,
     Sample expected_maximum,
     uint32_t expected_bucket_count) const {
   // SparseHistogram never has min/max/bucket_count limit.
   return false;
 }
 
 void SparseHistogram::Add(Sample value) {
   AddCount(value, 1);
 }
 
 void SparseHistogram::AddCount(Sample value, int count) {
   if (count <= 0) {
     NOTREACHED();
     return;
   }
   {
     base::AutoLock auto_lock(lock_);
-    samples_->Accumulate(value, count);
+    unlogged_samples_->Accumulate(value, count);
   }
 
   FindAndRunCallback(value);
 }
 
 std::unique_ptr<HistogramSamples> SparseHistogram::SnapshotSamples() const {
   std::unique_ptr<SampleMap> snapshot(new SampleMap(name_hash()));
 
   base::AutoLock auto_lock(lock_);
-  snapshot->Add(*samples_);
+  snapshot->Add(*unlogged_samples_);
+  snapshot->Add(*logged_samples_);
   return std::move(snapshot);
 }
 
 std::unique_ptr<HistogramSamples> SparseHistogram::SnapshotDelta() {
   DCHECK(!final_delta_created_);
 
   std::unique_ptr<SampleMap> snapshot(new SampleMap(name_hash()));
   base::AutoLock auto_lock(lock_);
-  snapshot->Add(*samples_);
+  snapshot->Add(*unlogged_samples_);
 
-  // Subtract what was previously logged and update that information.
-  snapshot->Subtract(*logged_samples_);
+  unlogged_samples_->Subtract(*snapshot);
   logged_samples_->Add(*snapshot);
   return std::move(snapshot);
 }
 
 std::unique_ptr<HistogramSamples> SparseHistogram::SnapshotFinalDelta() const {
   DCHECK(!final_delta_created_);
   final_delta_created_ = true;
 
   std::unique_ptr<SampleMap> snapshot(new SampleMap(name_hash()));
   base::AutoLock auto_lock(lock_);
-  snapshot->Add(*samples_);
+  snapshot->Add(*unlogged_samples_);
 
-  // Subtract what was previously logged and then return.
-  snapshot->Subtract(*logged_samples_);
   return std::move(snapshot);
 }
 
 void SparseHistogram::AddSamples(const HistogramSamples& samples) {
   base::AutoLock auto_lock(lock_);
-  samples_->Add(samples);
+  unlogged_samples_->Add(samples);
 }
 
 bool SparseHistogram::AddSamplesFromPickle(PickleIterator* iter) {
   base::AutoLock auto_lock(lock_);
-  return samples_->AddFromPickle(iter);
+  return unlogged_samples_->AddFromPickle(iter);
 }
 
 void SparseHistogram::WriteHTMLGraph(std::string* output) const {
   output->append("<PRE>");
   WriteAsciiImpl(true, "<br>", output);
   output->append("</PRE>");
 }
 
 void SparseHistogram::WriteAscii(std::string* output) const {
   WriteAsciiImpl(true, "\n", output);
 }
 
 bool SparseHistogram::SerializeInfoImpl(Pickle* pickle) const {
   return pickle->WriteString(histogram_name()) && pickle->WriteInt(flags());
 }
 
 SparseHistogram::SparseHistogram(const std::string& name)
     : HistogramBase(name),
-      samples_(new SampleMap(HashMetricName(name))),
-      logged_samples_(new SampleMap(samples_->id())) {}
+      unlogged_samples_(new SampleMap(HashMetricName(name))),
+      logged_samples_(new SampleMap(unlogged_samples_->id())) {}
 
 SparseHistogram::SparseHistogram(PersistentHistogramAllocator* allocator,
                                  const std::string& name,
                                  HistogramSamples::Metadata* meta,
                                  HistogramSamples::Metadata* logged_meta)
     : HistogramBase(name),
       // While other histogram types maintain a static vector of values with
       // sufficient space for both "active" and "logged" samples, with each
       // SampleVector being given the appropriate half, sparse histograms
       // have no such initial allocation. Each sample has its own record
       // attached to a single PersistentSampleMap by a common 64-bit identifier.
       // Since a sparse histogram has two sample maps (active and logged),
       // there must be two sets of sample records with diffent IDs. The
       // "active" samples use, for convenience purposes, an ID matching
       // that of the histogram while the "logged" samples use that number
       // plus 1.
-      samples_(new PersistentSampleMap(HashMetricName(name), allocator, meta)),
-      logged_samples_(
-          new PersistentSampleMap(samples_->id() + 1, allocator, logged_meta)) {
-}
+      unlogged_samples_(
+          new PersistentSampleMap(HashMetricName(name), allocator, meta)),
+      logged_samples_(new PersistentSampleMap(unlogged_samples_->id() + 1,
+                                              allocator,
+                                              logged_meta)) {}
 
 HistogramBase* SparseHistogram::DeserializeInfoImpl(PickleIterator* iter) {
   std::string histogram_name;
   int flags;
   if (!iter->ReadString(&histogram_name) || !iter->ReadInt(&flags)) {
     DLOG(ERROR) << "Pickle error decoding Histogram: " << histogram_name;
     return NULL;
   }
 
   flags &= ~HistogramBase::kIPCSerializationSourceFlag;
@@ skipping 68 matching lines @@
                                        std::string* output) const {
   StringAppendF(output,
                 "Histogram: %s recorded %d samples",
                 histogram_name().c_str(),
                 total_count);
   if (flags())
     StringAppendF(output, " (flags = 0x%x)", flags());
 }
 
 }  // namespace base