Support "shared" histograms between processes.

components/metrics/metrics_service.cc

 // Copyright 2014 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.
 
 //------------------------------------------------------------------------------
 // Description of the life cycle of a instance of MetricsService.
 //
 //  OVERVIEW
 //
 // A MetricsService instance is typically created at application startup.  It is
@@ skipping 115 matching lines @@
 
 #include <stddef.h>
 #include <algorithm>
 #include <utility>
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/location.h"
 #include "base/metrics/histogram_base.h"
 #include "base/metrics/histogram_macros.h"
+#include "base/metrics/histogram_persistence.h"
 #include "base/metrics/histogram_samples.h"
 #include "base/metrics/sparse_histogram.h"
 #include "base/metrics/statistics_recorder.h"
 #include "base/prefs/pref_registry_simple.h"
 #include "base/prefs/pref_service.h"
 #include "base/rand_util.h"
 #include "base/single_thread_task_runner.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/thread_task_runner_handle.h"
@@ skipping 587 matching lines @@
 
   // TODO(jar): Integrate bounds on log recording more consistently, so that we
   // can stop recording logs that are too big much sooner.
   if (log_manager_.current_log()->num_events() > kEventLimit) {
     UMA_HISTOGRAM_COUNTS("UMA.Discarded Log Events",
                          log_manager_.current_log()->num_events());
     log_manager_.DiscardCurrentLog();
     OpenNewLog();  // Start trivial log to hold our histograms.
   }
 
+  // If a persistent allocator is in use, update its internal histograms (such
+  // as how much memory is being used) before reporting.
+  base::PersistentMemoryAllocator* allocator =
+      base::GetPersistentHistogramMemoryAllocator();
+  if (allocator)
+    allocator->UpdateStaticHistograms();
+
   // Put incremental data (histogram deltas, and realtime stats deltas) at the
   // end of all log transmissions (initial log handles this separately).
   // RecordIncrementalStabilityElements only exists on the derived
   // MetricsLog class.
   MetricsLog* current_log = log_manager_.current_log();
   DCHECK(current_log);
   RecordCurrentEnvironment(current_log);
   base::TimeDelta incremental_uptime;
   base::TimeDelta uptime;
   GetUptimes(local_state_, &incremental_uptime, &uptime);
@@ skipping 340 matching lines @@
 void MetricsService::RecordCurrentEnvironment(MetricsLog* log) {
   std::vector<variations::ActiveGroupId> synthetic_trials;
   GetSyntheticFieldTrialsOlderThan(log->creation_time(), &synthetic_trials);
   log->RecordEnvironment(metrics_providers_.get(), synthetic_trials,
                          GetInstallDate(), GetMetricsReportingEnabledDate());
 }
 
 void MetricsService::RecordCurrentHistograms() {
   DCHECK(log_manager_.current_log());
   histogram_snapshot_manager_.PrepareDeltas(
+      base::StatisticsRecorder::begin(true), base::StatisticsRecorder::end(),
       base::Histogram::kNoFlags, base::Histogram::kUmaTargetedHistogramFlag);
 }
 
 void MetricsService::RecordCurrentStabilityHistograms() {
   DCHECK(log_manager_.current_log());
   histogram_snapshot_manager_.PrepareDeltas(
+      base::StatisticsRecorder::begin(true), base::StatisticsRecorder::end(),

[Alexei Svitkine (slow), 2016/01/18 19:25:36]

For all the calls to begin(), can you add a comment above explaining reasoning
for the true/false param, so it's obvious from the call site.

Particularly also the one in histogram_delta_serialization.cc.

[bcwhite, 2016/01/22 15:24:53]

Done.

       base::Histogram::kNoFlags, base::Histogram::kUmaStabilityHistogramFlag);
 }
 
 void MetricsService::LogCleanShutdown() {
   // Redundant setting to assure that we always reset this value at shutdown
   // (and that we don't use some alternate path, and not call LogCleanShutdown).
   clean_shutdown_status_ = CLEANLY_SHUTDOWN;
 
   clean_exit_beacon_.WriteBeaconValue(true);
   RecordCurrentState(local_state_);
@@ skipping 19 matching lines @@
                  base::Time::Now().ToTimeT());
 }
 
 void MetricsService::SkipAndDiscardUpload() {
   log_manager_.DiscardStagedLog();
   scheduler_->UploadCancelled();
   log_upload_in_progress_ = false;
 }
 
 }  // namespace metrics