Merge histograms from providers into StatisticsRecorder for display.

base/metrics/statistics_recorder.cc

Index: base/metrics/statistics_recorder.cc
diff --git a/base/metrics/statistics_recorder.cc b/base/metrics/statistics_recorder.cc
index 482845045f2bfcf08596846aabb032c277b0f048..3c1665c7e268f4cfbdfecbe39e200518b8518fcd 100644
--- a/base/metrics/statistics_recorder.cc
+++ b/base/metrics/statistics_recorder.cc
@@ -87,6 +87,7 @@ StatisticsRecorder::~StatisticsRecorder() {
   histograms_ = existing_histograms_.release();
   callbacks_ = existing_callbacks_.release();
   ranges_ = existing_ranges_.release();
+  providers_ = existing_providers_.release();
 }
 
 // static
@@ -113,6 +114,12 @@ bool StatisticsRecorder::IsActive() {
 }
 
 // static
+void StatisticsRecorder::RegisterHistogramProvider(
+    const WeakPtr<HistogramProvider>& provider) {
+  providers_->push_back(provider);
+}
+
+// static
 HistogramBase* StatisticsRecorder::RegisterOrDeleteDuplicate(
     HistogramBase* histogram) {
   HistogramBase* histogram_to_delete = nullptr;
@@ -307,6 +314,18 @@ HistogramBase* StatisticsRecorder::FindHistogram(base::StringPiece name) {
 }
 
 // static
+void StatisticsRecorder::ImportProvidedHistograms() {

[Alexei Svitkine (slow), 2017/01/27 16:22:03]

Can you add a thread check here?

[bcwhite, 2017/01/27 18:05:31]

Not sure if I can because base/ doesn't generally know about specific threads.

The providers, though, have thread-checkers that will break if not called on the
UI thread.

[Alexei Svitkine (slow), 2017/01/27 18:06:57]

Can you add base::ThreadChecker as a member and use
DCHECK(thread_checker_.CalledOnValidThread()) ?

[bcwhite, 2017/01/27 18:12:57]

These are static methods so there's no object to hold the thread_checker_.  A
static one could be created like the other static objects are, but I don't think
it's worth the complication.

+  if (!providers_)
+    return;
+
+  // Merge histogram data from each provider in turn.
+  for (const WeakPtr<HistogramProvider>& provider : *providers_) {
+    if (provider)

[Alexei Svitkine (slow), 2017/01/27 16:22:03]

Nit: Maybe add a comment here to mention this is check is because the weak
pointer may have been invalidated.

[bcwhite, 2017/01/27 18:05:31]

Done.

+      provider->MergeHistogramDeltas();
+  }
+}
+
+// static
 StatisticsRecorder::HistogramIterator StatisticsRecorder::begin(
     bool include_persistent) {
   DCHECK(histograms_);
@@ -346,6 +365,8 @@ void StatisticsRecorder::GetSnapshot(const std::string& query,
   if (!histograms_)
     return;
 
+  ImportGlobalPersistentHistograms();
+
   for (const auto& entry : *histograms_) {
     if (entry.second->histogram_name().find(query) != std::string::npos)
       snapshot->push_back(entry.second);
@@ -458,10 +479,12 @@ StatisticsRecorder::StatisticsRecorder() {
   existing_histograms_.reset(histograms_);
   existing_callbacks_.reset(callbacks_);
   existing_ranges_.reset(ranges_);
+  existing_providers_.reset(providers_);
 
   histograms_ = new HistogramMap;
   callbacks_ = new CallbackMap;
   ranges_ = new RangesMap;
+  providers_ = new HistogramProviders;
 
   InitLogOnShutdownWithoutLock();
 }
@@ -479,14 +502,17 @@ void StatisticsRecorder::Reset() {
   std::unique_ptr<HistogramMap> histograms_deleter;
   std::unique_ptr<CallbackMap> callbacks_deleter;
   std::unique_ptr<RangesMap> ranges_deleter;
+  std::unique_ptr<HistogramProviders> providers_deleter;
   {
     base::AutoLock auto_lock(lock_.Get());
     histograms_deleter.reset(histograms_);
     callbacks_deleter.reset(callbacks_);
     ranges_deleter.reset(ranges_);
+    providers_deleter.reset(providers_);
     histograms_ = nullptr;
     callbacks_ = nullptr;
     ranges_ = nullptr;
+    providers_ = nullptr;
   }
   // We are going to leak the histograms and the ranges.
 }
@@ -506,6 +532,8 @@ StatisticsRecorder::CallbackMap* StatisticsRecorder::callbacks_ = nullptr;
 // static
 StatisticsRecorder::RangesMap* StatisticsRecorder::ranges_ = nullptr;
 // static
+StatisticsRecorder::HistogramProviders* StatisticsRecorder::providers_;
+// static
 base::LazyInstance<base::Lock>::Leaky StatisticsRecorder::lock_ =
     LAZY_INSTANCE_INITIALIZER;