Display histograms from subprocesses in chrome://histograms

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 143 matching lines @@
 void SparseHistogram::AddSamples(const HistogramSamples& samples) {
   base::AutoLock auto_lock(lock_);
   samples_->Add(samples);
 }
 
 bool SparseHistogram::AddSamplesFromPickle(PickleIterator* iter) {
   base::AutoLock auto_lock(lock_);
   return samples_->AddFromPickle(iter);
 }
 
-void SparseHistogram::WriteHTMLGraph(std::string* output) const {
+void SparseHistogram::WriteHTMLGraph(const HistogramSamples* snapshot,
+                                     std::string* output) const {
   output->append("<PRE>");
-  WriteAsciiImpl(true, "<br>", output);
+  WriteAsciiImpl(true, "<br>", snapshot, output);
   output->append("</PRE>");
 }
 
-void SparseHistogram::WriteAscii(std::string* output) const {
-  WriteAsciiImpl(true, "\n", output);
+void SparseHistogram::WriteAscii(const HistogramSamples* snapshot,
+                                 std::string* output) const {
+  WriteAsciiImpl(true, "\n", snapshot, 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())) {}
@@ skipping 37 matching lines @@
 }
 
 void SparseHistogram::GetCountAndBucketData(Count* count,
                                             int64_t* sum,
                                             ListValue* buckets) const {
   // TODO(kaiwang): Implement. (See HistogramBase::WriteJSON.)
 }
 
 void SparseHistogram::WriteAsciiImpl(bool graph_it,
                                      const std::string& newline,
+                                     const HistogramSamples* snapshot,
                                      std::string* output) const {
-  // Get a local copy of the data so we are consistent.
-  std::unique_ptr<HistogramSamples> snapshot = SnapshotSamples();
+  std::unique_ptr<HistogramSamples> local_snapshot;
+  if (!snapshot) {
+    // Get local (stack) copies of all effectively volatile class data so
+    // that we are consistent across our output activities.
+    local_snapshot = SnapshotSamples();
+    snapshot = local_snapshot.get();
+  }
   Count total_count = snapshot->TotalCount();
   double scaled_total_count = total_count / 100.0;
 
   WriteAsciiHeader(total_count, output);
   output->append(newline);
 
   // Determine how wide the largest bucket range is (how many digits to print),
   // so that we'll be able to right-align starts for the graphical bars.
   // Determine which bucket has the largest sample count so that we can
   // normalize the graphical bar-width relative to that sample count.
@@ skipping 39 matching lines @@
                                        std::string* output) const {
   StringAppendF(output,
                 "Histogram: %s recorded %d samples",
                 histogram_name().c_str(),
                 total_count);
   if (flags() & ~kHexRangePrintingFlag)
     StringAppendF(output, " (flags = 0x%x)", flags() & ~kHexRangePrintingFlag);
 }
 
 }  // namespace base