Merge subprocess metrics into global StatisticsRecorder.

chrome/browser/metrics/subprocess_metrics_provider.h

 // Copyright 2016 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.
 
 #ifndef CHROME_BROWSER_METRICS_SUBPROCESS_METRICS_PROVIDER_H_
 #define CHROME_BROWSER_METRICS_SUBPROCESS_METRICS_PROVIDER_H_
 
 #include <memory>
 #include <set>
 
 #include "base/gtest_prod_util.h"
 #include "base/id_map.h"
 #include "base/scoped_observer.h"
 #include "base/threading/thread_checker.h"
 #include "components/metrics/metrics_provider.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 #include "content/public/browser/render_process_host_observer.h"
 
 namespace base {
 class PersistentHistogramAllocator;
 class SharedPersistentMemoryAllocator;
 }
 
-// SubprocessMetricsProvider gathers and logs histograms stored in shared
-// memory segments between processes.
+// SubprocessMetricsProvider gathers and merges histograms stored in shared
+// memory segments between processes. Merging occurs when a process exits,
+// when metrics are being collected for upload, or when something else needs
+// combined metrics (such as the chrome://histograms page).
 class SubprocessMetricsProvider : public metrics::MetricsProvider,
                                   public content::NotificationObserver,
                                   public content::RenderProcessHostObserver {
  public:
   SubprocessMetricsProvider();
   ~SubprocessMetricsProvider() override;
 
  private:
   friend class SubprocessMetricsProviderTest;
 
   // Indicates subprocess to be monitored with unique id for later reference.
   // Metrics reporting will read histograms from it and upload them to UMA.
   void RegisterSubprocessAllocator(
       int id,
       std::unique_ptr<base::PersistentHistogramAllocator> allocator);
 
   // Indicates that a subprocess has exited and is thus finished with the
   // allocator it was using.
   void DeregisterSubprocessAllocator(int id);
 
-  // Report all histograms of a given allocator to the snapshot-manager.
-  void RecordHistogramSnapshotsFromAllocator(
-      base::HistogramSnapshotManager* snapshot_manager,
+  // Merge all histograms of a given allocator to the global StatisticsRecorder.
+  // This is called periodically during UMA metrics collection (if enabled) and
+  // possibly on-demand for other purposes.
+  void MergeHistogramDeltasFromAllocator(
       int id,
       base::PersistentHistogramAllocator* allocator);
 
   // metrics::MetricsProvider:
-  void OnDidCreateMetricsLog() override;
-  void OnRecordingEnabled() override;
-  void OnRecordingDisabled() override;
-  void RecordHistogramSnapshots(
-      base::HistogramSnapshotManager* snapshot_manager) override;
+  void MergeHistogramDeltas() override;
 
   // content::NotificationObserver:
   void Observe(int type,
                const content::NotificationSource& source,
                const content::NotificationDetails& details) override;
 
   // content::RenderProcessHostObserver:
   void RenderProcessReady(content::RenderProcessHost* host) override;
   void RenderProcessExited(content::RenderProcessHost* host,
                            base::TerminationStatus status,
                            int exit_code) override;
   void RenderProcessHostDestroyed(content::RenderProcessHost* host) override;
 
   base::ThreadChecker thread_checker_;
 
   // Object for registing notification requests.
   content::NotificationRegistrar registrar_;
 
   // All of the shared-persistent-allocators for known sub-processes.
   using AllocatorByIdMap =
       IDMap<base::PersistentHistogramAllocator, IDMapOwnPointer, int>;
   AllocatorByIdMap allocators_by_id_;
 
-  // Allocators that are no longer attached to a subprocess, to be released
-  // once the last data contained therein has been reported.
-  std::vector<std::unique_ptr<base::PersistentHistogramAllocator>>
-      allocators_for_exited_processes_;
-  std::vector<std::unique_ptr<base::PersistentHistogramAllocator>>
-      allocators_to_release_;
-
   // Track all observed render processes to un-observe them on exit.
   ScopedObserver<content::RenderProcessHost, SubprocessMetricsProvider>
       scoped_observer_;
 
-  // Flag indicating if metrics recording is enabled. Allocators will not
-  // live past the death of the subprocess if it is not.
-  bool metrics_recording_enabled_ = false;
-
   DISALLOW_COPY_AND_ASSIGN(SubprocessMetricsProvider);
 };
 
 #endif  // CHROME_BROWSER_METRICS_SUBPROCESS_METRICS_PROVIDER_H_