Metrics provider for statistical stack profiler

components/metrics/call_stack_profile_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 "components/metrics/call_stack_profile_metrics_provider.h"
+
+#include <cstring>
+#include <map>
+#include <utility>
+
+#include "base/logging.h"
+#include "base/macros.h"
+#include "base/profiler/stack_sampling_profiler.h"
+#include "components/metrics/metrics_hashes.h"
+#include "components/metrics/proto/chrome_user_metrics_extension.pb.h"
+
+using base::StackSamplingProfiler;
+
+namespace metrics {
+
+namespace {
+
+// The protobuf expects the MD5 checksum prefix of the module name.
+uint64 HashModuleFilename(const base::FilePath& filename) {
+  const base::FilePath::StringType basename = filename.BaseName().value();

[Ilya Sherman, 2015/03/19 00:10:19]

nit: Probably no need to make a copy here, right?

[Mike Wittman, 2015/03/19 00:56:58]

Done.

[Mike Wittman, 2015/03/19 21:51:18]

Actually, we do need to make a copy here. value() returns a reference to the
path in the temporary object produced by BaseName(), which goes away.

[Ilya Sherman, 2015/03/19 22:00:11]

Wait, really?  Fascinating!  If I'm understanding correctly, then the following
two snippets have different behavior:

const base::FilePath& path = filename.BaseName();
const base::FilePath::StringType& basename = path.value();

const base::FilePath::StringType& basename = filename.BaseName().value();

Dear C++, that is super confusing.  (No follow-up needed, I'm just really
intrigued by this C++ wart.)

+  // Copy the bytes in basename into a string buffer.
+  std::string name_bytes(basename.size() * sizeof(base::FilePath::CharType),
+                         '\0');
+  memcpy(&name_bytes[0], &basename[0],
+         basename.size() * sizeof(base::FilePath::CharType));

[Ilya Sherman, 2015/03/19 00:10:19]

nit: Please cache this computation, rather than performing it twice -- it would
be really bad to have a mismatch between the sizes used in one location vs. the
other.

[Mike Wittman, 2015/03/19 00:56:58]

Done.

+  return HashMetricName(name_bytes);
+}
+
+// Transcode |sample| into |proto_sample|, using base addresses in |modules| to
+// compute module instruction pointer offsets.
+void CopySampleToProto(
+    const StackSamplingProfiler::Sample& sample,
+    const std::vector<StackSamplingProfiler::Module>& modules,
+    CallStackProfile::Sample* proto_sample) {
+  for (const StackSamplingProfiler::Frame& frame : sample) {
+    CallStackEntry* call_stack_entry = proto_sample->add_entry();
+    // A frame may not have a valid module. If so we can't compute the

[Ilya Sherman, 2015/03/19 00:10:19]

nit: "If so we can't" -> "If so, we can't"

[Mike Wittman, 2015/03/19 00:56:58]

Done.

+    // instruction pointer offset, and we don't want to send bare pointers, so
+    // leave call_stack_entry empty.
+    if (frame.module_index < 0)
+      continue;
+    int64 module_offset =
+        reinterpret_cast<const char*>(frame.instruction_pointer) -
+        reinterpret_cast<const char*>(modules[frame.module_index].base_address);
+    DCHECK_GE(module_offset, 0);
+    call_stack_entry->set_address(static_cast<uint64>(module_offset));
+    call_stack_entry->set_module_id_index(frame.module_index);
+  }
+}
+
+// Transcode |profile| into |proto_profile|.
+void CopyProfileToProto(
+    const StackSamplingProfiler::Profile& profile,
+    CallStackProfile* proto_profile) {
+  if (profile.samples.empty())
+    return;
+
+  if (profile.preserve_sample_ordering) {
+    // Collapse only consecutive repeated samples together.
+    CallStackProfile::Sample* current_sample_proto = nullptr;
+    for (auto it = profile.samples.begin(); it != profile.samples.end(); ++it) {
+      if (!current_sample_proto || *it != *(it - 1)) {
+        current_sample_proto = proto_profile->add_sample();
+        CopySampleToProto(*it, profile.modules, current_sample_proto);
+        current_sample_proto->set_count(1);
+      } else {
+        current_sample_proto->set_count(current_sample_proto->count() + 1);
+      }
+    }
+  } else {
+    // Collapse all repeated samples together.
+    std::map<StackSamplingProfiler::Sample, int> sample_index;
+    for (auto it = profile.samples.begin(); it != profile.samples.end(); ++it) {
+      auto location = sample_index.find(*it);
+      if (location == sample_index.end()) {
+        CallStackProfile::Sample* sample_proto = proto_profile->add_sample();
+        CopySampleToProto(*it, profile.modules, sample_proto);
+        sample_proto->set_count(1);
+        sample_index.insert(
+            std::make_pair(
+                *it, static_cast<int>(proto_profile->sample().size()) - 1));
+      } else {
+        CallStackProfile::Sample* sample_proto =
+            proto_profile->mutable_sample()->Mutable(location->second);
+        sample_proto->set_count(sample_proto->count() + 1);
+      }
+    }
+  }
+
+  for (const StackSamplingProfiler::Module& module : profile.modules) {
+    ModuleIdentifier* module_id = proto_profile->add_module_id();
+    module_id->set_build_id(module.id);
+    module_id->set_name_md5_prefix(HashModuleFilename(module.filename));
+  }
+
+  proto_profile->set_profile_duration_ms(
+      profile.profile_duration.InMilliseconds());
+  proto_profile->set_sampling_period_ms(
+      profile.sampling_period.InMilliseconds());
+}
+}  // namespace
+
+CallStackProfileMetricsProvider::CallStackProfileMetricsProvider() {}
+
+CallStackProfileMetricsProvider::~CallStackProfileMetricsProvider() {}
+
+void CallStackProfileMetricsProvider::ProvideGeneralMetrics(
+    ChromeUserMetricsExtension* uma_proto) {
+  std::vector<StackSamplingProfiler::Profile> profiles;
+  if (!source_profiles_for_test_.empty())
+    profiles.swap(source_profiles_for_test_);
+  else
+    StackSamplingProfiler::GetPendingProfiles(&profiles);
+
+  for (const StackSamplingProfiler::Profile& profile : profiles) {
+    CallStackProfile* call_stack_profile =
+        uma_proto->add_sampled_profile()->mutable_call_stack_profile();
+    CopyProfileToProto(profile, call_stack_profile);
+  }
+}
+
+void CallStackProfileMetricsProvider::SetSourceProfilesForTesting(
+    const std::vector<StackSamplingProfiler::Profile>& profiles) {
+  source_profiles_for_test_ = profiles;
+}
+
+}  // namespace metrics