Use persistent memory for receiving metrics from sub-processes.

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/memory/weak_ptr.h"
 #include "base/scoped_observer.h"
 #include "base/threading/thread_checker.h"
 #include "components/metrics/metrics_provider.h"
+#include "content/public/browser/browser_child_process_observer.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 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::BrowserChildProcessObserver,
                                   public content::NotificationObserver,
                                   public content::RenderProcessHostObserver {
  public:
   SubprocessMetricsProvider();
   ~SubprocessMetricsProvider() override;
 
+  // Start tracking sub-processes. This is called separately rather than being
+  // set in the constructor because library code that checks for calling on
+  // the correct thread (i.e. UI thread) can break tests because test threads
+  // don't have that ID.
+  void EnableSubprocessTracking();
+
  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);
 
   // 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 MergeHistogramDeltas() override;
 
+  // content::BrowserChildProcessObserver:
+  void BrowserChildProcessHostConnected(
+      const content::ChildProcessData& data) override;
+  void BrowserChildProcessHostDisconnected(
+      const content::ChildProcessData& data) override;
+  void BrowserChildProcessCrashed(
+      const content::ChildProcessData& data,
+      int exit_code) override;
+  void BrowserChildProcessKilled(
+      const content::ChildProcessData& data,
+      int exit_code) 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;
 
+  // Gets a histogram allocator from a subprocess. This must be called on
+  // the IO thread.
+  static std::unique_ptr<base::PersistentHistogramAllocator>
+  GetSubprocessHistogramAllocatorOnIOThread(int id);
+
   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_;
 
   // Track all observed render processes to un-observe them on exit.
   ScopedObserver<content::RenderProcessHost, SubprocessMetricsProvider>
       scoped_observer_;
 
+  base::WeakPtrFactory<SubprocessMetricsProvider> weak_ptr_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(SubprocessMetricsProvider);
 };
 
 #endif  // CHROME_BROWSER_METRICS_SUBPROCESS_METRICS_PROVIDER_H_