Merge histograms from providers into StatisticsRecorder for display.

base/metrics/statistics_recorder.h

 // 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.
 
 // StatisticsRecorder holds all Histograms and BucketRanges that are used by
 // Histograms in the system. It provides a general place for
 // Histograms/BucketRanges to register, and supports a global API for accessing
 // (i.e., dumping, or graphing) the data.
 
 #ifndef BASE_METRICS_STATISTICS_RECORDER_H_
 #define BASE_METRICS_STATISTICS_RECORDER_H_
 
 #include <stdint.h>
 
 #include <list>
 #include <map>
 #include <memory>
 #include <string>
 #include <vector>
 
 #include "base/base_export.h"
 #include "base/callback.h"
 #include "base/gtest_prod_util.h"
 #include "base/lazy_instance.h"
 #include "base/macros.h"
+#include "base/memory/weak_ptr.h"
 #include "base/metrics/histogram_base.h"
 #include "base/strings/string_piece.h"
 #include "base/synchronization/lock.h"
 
 namespace base {
 
 class BucketRanges;
 
 class BASE_EXPORT StatisticsRecorder {
  public:
@@ skipping 19 matching lines @@
         return false;
 
       // Fall back to an actual string comparison. The lengths are the same
       // so a simple memory-compare is sufficient. This is slightly more
       // efficient than calling operator<() for StringPiece which would
       // again have to check lengths before calling wordmemcmp().
       return wordmemcmp(data(), rhs.data(), length()) < 0;
     }
   };
 
+  // An interface class that allows the StatisticsRecorder to forcibly merge
+  // histograms from providers when necessary.
+  class HistogramProvider {
+   public:
+    // Merges all histogram information into the global versions.
+    virtual void MergeHistogramDeltas() = 0;
+  };
+
   typedef std::map<StringKey, HistogramBase*> HistogramMap;
   typedef std::vector<HistogramBase*> Histograms;
+  typedef std::vector<WeakPtr<HistogramProvider>> HistogramProviders;
 
   // A class for iterating over the histograms held within this global resource.
   class BASE_EXPORT HistogramIterator {
    public:
     HistogramIterator(const HistogramMap::iterator& iter,
                       bool include_persistent);
     HistogramIterator(const HistogramIterator& rhs);  // Must be copyable.
     ~HistogramIterator();
 
     HistogramIterator& operator++();
@@ skipping 17 matching lines @@
   };
 
   ~StatisticsRecorder();
 
   // Initializes the StatisticsRecorder system. Safe to call multiple times.
   static void Initialize();
 
   // Find out if histograms can now be registered into our list.
   static bool IsActive();
 
+  // Register a provider of histograms that can be called to merge those into
+  // the global StatisticsRecorder.

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

Nit: Mention ImportProvidedHistograms() here.

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

Done.

+  static void RegisterHistogramProvider(
+      const WeakPtr<HistogramProvider>& provider);
+
   // Register, or add a new histogram to the collection of statistics. If an
   // identically named histogram is already registered, then the argument
   // |histogram| will deleted.  The returned value is always the registered
   // histogram (either the argument, or the pre-existing registered histogram).
   static HistogramBase* RegisterOrDeleteDuplicate(HistogramBase* histogram);
 
   // Register, or add a new BucketRanges. If an identically BucketRanges is
   // already registered, then the argument |ranges| will deleted. The returned
   // value is always the registered BucketRanges (either the argument, or the
   // pre-existing one).
@@ skipping 13 matching lines @@
   // Method for extracting histograms which were marked for use by UMA.
   static void GetHistograms(Histograms* output);
 
   // Method for extracting BucketRanges used by all histograms registered.
   static void GetBucketRanges(std::vector<const BucketRanges*>* output);
 
   // Find a histogram by name. It matches the exact name. This method is thread
   // safe.  It returns NULL if a matching histogram is not found.
   static HistogramBase* FindHistogram(base::StringPiece name);
 
+  // Imports histograms from providers. This must be called on the UI thread.
+  static void ImportProvidedHistograms();
+
   // Support for iterating over known histograms.
   static HistogramIterator begin(bool include_persistent);
   static HistogramIterator end();
 
   // GetSnapshot copies some of the pointers to registered histograms into the
   // caller supplied vector (Histograms). Only histograms which have |query| as
   // a substring are copied (an empty string will process all registered
   // histograms).
   static void GetSnapshot(const std::string& query, Histograms* snapshot);
 
@@ skipping 66 matching lines @@
   // Initialize implementation but without lock. Caller should guard
   // StatisticsRecorder by itself if needed (it isn't in unit tests).
   void InitLogOnShutdownWithoutLock();
 
   // These are copies of everything that existed when the (test) Statistics-
   // Recorder was created. The global ones have to be moved aside to create a
   // clean environment.
   std::unique_ptr<HistogramMap> existing_histograms_;
   std::unique_ptr<CallbackMap> existing_callbacks_;
   std::unique_ptr<RangesMap> existing_ranges_;
+  std::unique_ptr<HistogramProviders> existing_providers_;
 
   bool vlog_initialized_ = false;
 
   static void Reset();
   static void DumpHistogramsToVlog(void* instance);
 
   static HistogramMap* histograms_;
   static CallbackMap* callbacks_;
   static RangesMap* ranges_;
+  static HistogramProviders* providers_;
 
   // Lock protects access to above maps. This is a LazyInstance to avoid races
   // when the above methods are used before Initialize(). Previously each method
   // would do |if (!lock_) return;| which would race with
   // |lock_ = new Lock;| in StatisticsRecorder(). http://crbug.com/672852.
   static base::LazyInstance<base::Lock>::Leaky lock_;
 
   DISALLOW_COPY_AND_ASSIGN(StatisticsRecorder);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_STATISTICS_RECORDER_H_