Create and pass shared-histogram-allocator from browser to renderer.

chrome/browser/metrics/subprocess_metrics_provider.cc

+// 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.
+
+#include "chrome/browser/metrics/subprocess_metrics_provider.h"
+
+#include "base/logging.h"
+#include "base/metrics/histogram_base.h"
+#include "base/metrics/histogram_macros.h"
+#include "base/metrics/persistent_histogram_allocator.h"
+#include "base/metrics/persistent_memory_allocator.h"
+#include "components/metrics/metrics_service.h"
+#include "content/public/browser/notification_service.h"
+#include "content/public/browser/notification_types.h"
+#include "content/public/browser/render_process_host.h"
+
+SubprocessMetricsProvider::SubprocessMetricsProvider()
+    : scoped_observer_(this) {
+  registrar_.Add(this, content::NOTIFICATION_RENDERER_PROCESS_CREATED,
+                 content::NotificationService::AllBrowserContextsAndSources());
+}
+
+SubprocessMetricsProvider::~SubprocessMetricsProvider() {}
+
+void SubprocessMetricsProvider::RegisterSubprocessAllocator(
+    int id,
+    scoped_ptr<base::PersistentHistogramAllocator> allocator) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK(!allocators_by_id_.Lookup(id));
+
+  // Map is "MapOwnPointer" so transfer ownership to it.
+  allocators_by_id_.AddWithID(allocator.release(), id);
+}
+
+void SubprocessMetricsProvider::DeregisterSubprocessAllocator(int id) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
+  if (!allocators_by_id_.Lookup(id))
+    return;
+
+  // Extract the matching allocator from the list of active ones.
+  scoped_ptr<base::PersistentHistogramAllocator> allocator(
+      allocators_by_id_.Replace(id, nullptr));
+  allocators_by_id_.Remove(id);
+  DCHECK(allocator);
+
+  // If metrics recording is enabled, transfer the allocator to the "release"
+  // list. The allocator will continue to live (and keep the associated shared
+  // memory alive) until the next upload after which it will be released.
+  // Otherwise, the allocator and its memory will be released when the
+  // scoped_ptr goes out of scope at the end of this method.
+  if (metrics_recording_enabled_)
+    allocators_to_release_.push_back(std::move(allocator));
+}
+
+void SubprocessMetricsProvider::OnRecordingEnabled() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
+  metrics_recording_enabled_ = true;
+}
+
+void SubprocessMetricsProvider::OnRecordingDisabled() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
+  metrics_recording_enabled_ = false;
+  allocators_to_release_.clear();
+}
+
+void SubprocessMetricsProvider::RecordHistogramSnapshotsFromAllocator(
+    base::HistogramSnapshotManager* snapshot_manager,
+    int id,
+    base::PersistentHistogramAllocator* allocator) {
+  DCHECK(allocator);
+
+  int histogram_count = 0;
+  base::PersistentHistogramAllocator::Iterator hist_iter;
+  allocator->CreateIterator(&hist_iter);
+  while (true) {
+    scoped_ptr<base::HistogramBase> histogram =
+        allocator->GetNextHistogram(&hist_iter);
+    if (!histogram)
+      break;
+    snapshot_manager->PrepareDeltaTakingOwnership(std::move(histogram));
+    ++histogram_count;
+  }
+
+  DVLOG(1) << "Reported " << histogram_count << " histograms from subprocess #"
+           << id;
+}
+
+void SubprocessMetricsProvider::RecordHistogramSnapshots(
+    base::HistogramSnapshotManager* snapshot_manager) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
+  for (AllocatorByIdMap::iterator iter(&allocators_by_id_); !iter.IsAtEnd();
+       iter.Advance()) {
+    RecordHistogramSnapshotsFromAllocator(
+        snapshot_manager, iter.GetCurrentKey(), iter.GetCurrentValue());
+  }
+
+  for (auto& allocator : allocators_to_release_)
+    RecordHistogramSnapshotsFromAllocator(snapshot_manager, 0, allocator.get());
+
+  UMA_HISTOGRAM_COUNTS_100(
+      "UMA.SubprocessMetricsProvider.SubproccessCount",

[Alexei Svitkine (slow), 2016/03/31 22:00:57]

Add this to histograms.xml please.

[bcwhite, 2016/03/31 23:53:47]

Done.

+      allocators_by_id_.size() + allocators_to_release_.size());
+
+  // The snapshot-manager has taken ownership of the histograms but needs
+  // access to only the histogram objects, not "sample" data it uses. Thus,
+  // it is safe to release shared-memory segments without waiting for the
+  // snapshot-manager to "finish".
+  allocators_to_release_.clear();
+}
+
+void SubprocessMetricsProvider::Observe(
+    int type,
+    const content::NotificationSource& source,
+    const content::NotificationDetails& details) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DCHECK_EQ(content::NOTIFICATION_RENDERER_PROCESS_CREATED, type);
+
+  content::RenderProcessHost* host =
+      content::Source<content::RenderProcessHost>(source).ptr();
+
+  // Sometimes, the same host will cause multiple notifications in tests so
+  // could possibly do the same in a release build.
+  if (!scoped_observer_.IsObserving(host))
+    scoped_observer_.Add(host);
+}
+
+void SubprocessMetricsProvider::RenderProcessReady(
+    content::RenderProcessHost* host) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
+  // If the render-process-host passed a persistent-memory-allocator to the
+  // renderer process, extract it and register it here.
+  scoped_ptr<base::SharedPersistentMemoryAllocator> allocator =
+      host->ExtractMetricsAllocator();
+  if (allocator) {
+    RegisterSubprocessAllocator(
+        host->GetID(),
+        make_scoped_ptr(new base::PersistentHistogramAllocator(
+            std::move(allocator))));
+  }
+}
+
+void SubprocessMetricsProvider::RenderProcessHostDestroyed(
+    content::RenderProcessHost* host) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+
+  DeregisterSubprocessAllocator(host->GetID());
+  scoped_observer_.Remove(host);
+}