Persist setup metrics and have Chrome report them during UMA upload.

chrome/browser/metrics/chrome_setup_metrics_provider.cc

+// Copyright 2015 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/chrome_setup_metrics_provider.h"
+
+#include <vector>
+
+#include "base/command_line.h"
+#include "base/files/file.h"
+#include "base/files/file_util.h"
+#include "base/files/memory_mapped_file.h"
+#include "base/logging.h"
+#include "base/metrics/histogram_base.h"
+#include "base/metrics/persistent_memory_allocator.h"
+#include "base/prefs/pref_service.h"
+#include "base/threading/worker_pool.h"
+#include "base/time/time.h"
+#include "chrome/installer/util/google_update_constants.h"
+#include "components/metrics/metrics_pref_names.h"
+#include "components/metrics/metrics_service.h"
+
+
+ChromeSetupMetricsProvider::ChromeSetupMetricsProvider(
+    metrics::MetricsService* metrics_service,
+    PrefService* local_state)
+    : metrics_found_(0),
+      metrics_service_(metrics_service),
+      pref_service_(local_state),
+      program_directory_(base::CommandLine::ForCurrentProcess()->GetProgram()
+                             .DirName()) {
+  // Don't do any further actions if metrics_service is not valid (for testing).
+  if (!metrics_service_)
+    return;
+
+  // Start a background check for pending setup metrics so it can be uploaded
+  // during the initial report.
+  bool posted = base::WorkerPool::PostTask(
+    FROM_HERE,
+    base::Bind(&ChromeSetupMetricsProvider::CheckForSetupMetrics,

[Alexei Svitkine (slow), 2015/12/21 16:54:53]

In Chromium code, it's best practice to not have the same object instance be
accessed from multiple threads. You can search chromium-dev for discussions on
this topic.

Often, a good structure for the code is to have the work that happens on the
other thread be done in a free standing function in an anon namespace that will
pass its results back to the UI thread object via a callback.

[bcwhite, 2015/12/22 12:51:30]

Okay.  I'm rewriting this to support multiple files, both once-written and
constantly-updated.  I'll keep that in mind.

+               base::Unretained(this)),
+    false);
+  DCHECK(posted);
+}
+
+ChromeSetupMetricsProvider::~ChromeSetupMetricsProvider() {
+  // Destruction of this object can lead to failures because of a task
+  // posted on the Worker Pool or because the owned Memory Allocator has
+  // been passed to the Metrics Service. Both cases can only occur if
+  // a Metrics Service has been provided (i.e. not during testing).
+  if (metrics_service_) {
+    NOTREACHED();
+    // Removing the allocator may not be sufficient to avoid a crash (some
+    // Histogram could still be pointing to the memory) but it's the best
+    // that can be done.
+    if (metrics_allocator_)
+      metrics_service_->RemovePersistentMemorySegment(metrics_allocator_.get());
+  }
+}
+
+void ChromeSetupMetricsProvider::OnDidCreateMetricsLog() {
+  if (metrics_allocator_) {
+    // If an allocator has been created then the previous log collected all
+    // the metrics. The allocator can be released and the preferences updated
+    // to make sure it isn't reported again.
+    pref_service_->SetInt64(metrics::prefs::kSetupMetricsLastSeen,
+                            base::Time::Now().ToInternalValue());
+    if (metrics_service_)
+      metrics_service_->RemovePersistentMemorySegment(metrics_allocator_.get());

[Alexei Svitkine (slow), 2015/12/21 16:54:53]

Can this functionality be done by a different helper class than metrics service?
MetricsService is already pretty complex, so if we can avoid adding more things
directly to it, it would be preferable.

[bcwhite, 2015/12/22 12:51:30]

Not really.  MetricsService is what owns the HSM and flattener, hence it
controls how everything gets merged.

+    metrics_allocator_.reset();
+    metrics_found_.store(false);
+    return;
+  }
+
+  if (metrics_found_.load(std::memory_order_acquire)) {  // ACQ metrics_file
+    // A new file of setup metrics has been found. Attach to it and add it to
+    // the list of persistent allocators that need to have metrics reported.
+    DCHECK(metrics_file_);
+    if (base::FilePersistentMemoryAllocator::IsFileAcceptable(*metrics_file_)) {
+      metrics_allocator_.reset(new base::FilePersistentMemoryAllocator(
+                                   metrics_file_.release(), 0, std::string()));
+      if (!metrics_allocator_->IsCorrupt()) {
+        if (metrics_service_) {
+          metrics_service_->AddPersistentMemorySegment(
+              metrics_allocator_.get());
+        }
+        return;
+      }
+    }
+    // Something is fundamentally wrong with the file. Ignore it.
+    LOG(ERROR) << "Setup metrics file \""
+               << GetSetupMetricsFile().AsUTF8Unsafe()
+               << "\" is not valid -- ignored.";
+    metrics_allocator_.reset();
+    pref_service_->SetInt64(metrics::prefs::kSetupMetricsLastSeen,
+                            base::Time::Now().ToInternalValue());
+    return;
+  }
+
+  // Don't do any further actions if metrics_service is not valid (for testing).
+  if (!metrics_service_)
+    return;
+
+  // Nothing else is going on so schedule a check to see if there are new
+  // setup metrics to load. If so, they will be reported during the next
+  // collection run after this one. The check is run off of the worker-
+  // pool so as to not cause delays on the main UI thread (which is currently
+  // where metric collection is done).
+  bool posted = base::WorkerPool::PostTask(
+    FROM_HERE,
+    base::Bind(&ChromeSetupMetricsProvider::CheckForSetupMetrics,
+               base::Unretained(this)),
+    false);
+  DCHECK(posted);
+}
+
+base::FilePath ChromeSetupMetricsProvider::GetSetupMetricsFile() {
+  return program_directory_.AppendASCII(
+      google_update::kSetupHistogramAllocatorName);
+}
+
+void ChromeSetupMetricsProvider::CheckForSetupMetrics() {
+  DCHECK(!metrics_found_.load());
+  DCHECK(!metrics_file_);
+
+  base::File::Info info;
+  if (!base::GetFileInfo(GetSetupMetricsFile(), &info) ||
+      info.is_directory || info.size == 0) {
+    return;
+  }
+
+  const base::Time last_seen = base::Time::FromInternalValue(
+      pref_service_->GetInt64(metrics::prefs::kSetupMetricsLastSeen));
+  if (last_seen >= info.last_modified)
+    return;
+
+  // A new file of setup metrics has been found. Map it into memory.
+  metrics_file_.reset(new base::MemoryMappedFile());
+  metrics_file_->Initialize(GetSetupMetricsFile());
+
+  // Tell main thread that metrics have been found.
+  metrics_found_.store(true, std::memory_order_release);  // REL metrics_file
+}
+
+void ChromeSetupMetricsProvider::SetProgramDirectory(
+    const base::FilePath& dir) {
+  program_directory_ = dir;
+}