Updated metric Distribution and Timer utils.

[ Merge of http://go/wvgerrit/137811 ]

Renamed TimerMetric to Timer.  Timer is used to generate durations
included in metrics, but is not a metric itself.  The method of
getting the current time did not require creating an instance of
std::steady_clock.

Updated Distribution and Timer to use default initializers instead of
constructor initialization list.

Bug: 204946540
Test: Metric unit tests
Change-Id: I7ed291b586347dd0b7ab305960883bec04637315

libwvdrmengine/cdm/core/include/cdm_session.h

@@ -266,8 +266,8 @@ class CdmSession {
   // instance variables
   std::shared_ptr<metrics::SessionMetrics> metrics_;
   metrics::CryptoMetrics* crypto_metrics_;
-  metrics::TimerMetric life_span_;
+  metrics::Timer life_span_;
-  metrics::TimerMetric license_request_latency_;
+  metrics::Timer license_request_latency_;
   CdmKeyRequestType key_request_type_;
 
   bool initialized_;

libwvdrmengine/cdm/core/include/crypto_session.h

@@ -479,7 +479,7 @@ class CryptoSession {
   };
 
   metrics::CryptoMetrics* metrics_;
-  metrics::TimerMetric life_span_;
+  metrics::Timer life_span_;
   uint32_t system_id_;
 
   bool open_;

libwvdrmengine/cdm/metrics/include/distribution.h

@@ -4,12 +4,12 @@
 //
 // This file contains the definition of a Distribution class which computes
 // the distribution values of a series of samples.
-
 #ifndef WVCDM_METRICS_DISTRIBUTION_H_
 #define WVCDM_METRICS_DISTRIBUTION_H_
-
 #include <stdint.h>
 
+#include <limits>
+
 namespace wvcdm {
 namespace metrics {
 // The Distribution class holds statistics about a series of values that the
@@ -25,7 +25,7 @@ namespace metrics {
 //   dist.Count();  // Returns 2.
 class Distribution {
  public:
-  Distribution();
+  Distribution() {}
 
   // Uses the provided sample value to update the computed statistics.
   void Record(float value);
@@ -41,11 +41,11 @@ class Distribution {
   }
 
  private:
-  uint64_t count_;
+  uint64_t count_ = 0;
-  float min_;
+  float min_ = std::numeric_limits<float>::max();
-  float max_;
+  float max_ = std::numeric_limits<float>::lowest();
-  float mean_;
+  float mean_ = 0.0f;
-  double sum_squared_deviation_;
+  double sum_squared_deviation_ = 0.0;
 };
 }  // namespace metrics
 }  // namespace wvcdm

libwvdrmengine/cdm/metrics/include/metrics_collections.h

@@ -51,7 +51,7 @@
 //       sts);
 #define M_TIME(CALL, GROUP, METRIC, ...)                 \
   if (GROUP) {                                           \
-    wvcdm::metrics::TimerMetric timer;                   \
+    wvcdm::metrics::Timer timer;                         \
     timer.Start();                                       \
     CALL;                                                \
     (GROUP)->METRIC.Record(timer.AsUs(), ##__VA_ARGS__); \
@@ -488,7 +488,7 @@ class EngineMetrics {
   std::vector<std::shared_ptr<metrics::SessionMetrics>>
       completed_session_metrics_list_;
   // This is used to populate the engine lifespan metric
-  metrics::TimerMetric life_span_internal_;
+  metrics::Timer life_span_internal_;
   CryptoMetrics crypto_metrics_;
   std::string app_package_name_;
 

libwvdrmengine/cdm/metrics/include/timer_metric.h

@@ -7,10 +7,9 @@
 
 namespace wvcdm {
 namespace metrics {
-class TimerMetric {
+class Timer {
  public:
-  // Constructs a new TimerMetric.
+  Timer() {}
-  explicit TimerMetric() : is_started_(false) {}
   // Starts the clock running. If the clock was previously set, this resets it.
   // IsStarted will return true after this call.
   void Start();
@@ -25,9 +24,8 @@ class TimerMetric {
   double AsUs() const;
 
  private:
-  std::chrono::steady_clock clock_;
   std::chrono::time_point<std::chrono::steady_clock> start_;
-  bool is_started_;
+  bool is_started_ = false;
 };
 }  // namespace metrics
 }  // namespace wvcdm

libwvdrmengine/cdm/metrics/src/distribution.cpp

@@ -3,27 +3,15 @@
 // Agreement.
 //
 // This file contains the definitions for the Distribution class members.
-
 #include "distribution.h"
 
-#include <float.h>
-
 namespace wvcdm {
 namespace metrics {
-Distribution::Distribution()
-    : count_(0ULL),
-      min_(FLT_MAX),
-      max_(-FLT_MAX),
-      mean_(0.0),
-      sum_squared_deviation_(0.0) {}
-
 void Distribution::Record(float value) {
   // Using method of provisional means.
-  float deviation = value - mean_;
+  const float deviation = value - mean_;
-  mean_ = mean_ + (deviation / ++count_);
+  mean_ += (deviation / ++count_);
-  sum_squared_deviation_ =
+  sum_squared_deviation_ += (deviation * (value - mean_));
-      sum_squared_deviation_ + (deviation * (value - mean_));
-
   min_ = min_ < value ? min_ : value;
   max_ = max_ > value ? max_ : value;
 }

libwvdrmengine/cdm/metrics/src/timer_metric.cpp

@@ -5,19 +5,26 @@
 
 namespace wvcdm {
 namespace metrics {
-void TimerMetric::Start() {
+using ClockType = std::chrono::steady_clock;
-  start_ = clock_.now();
+using TimePoint = std::chrono::time_point<ClockType>;
+
+void Timer::Start() {
+  start_ = ClockType::now();
   is_started_ = true;
 }
 
-void TimerMetric::Clear() { is_started_ = false; }
+void Timer::Clear() { is_started_ = false; }
 
-double TimerMetric::AsMs() const {
+double Timer::AsMs() const {
-  return (clock_.now() - start_) / std::chrono::milliseconds(1);
+  if (!is_started_) return 0.0;
+  const TimePoint end = ClockType::now();
+  return (end - start_) / std::chrono::milliseconds(1);
 }
 
-double TimerMetric::AsUs() const {
+double Timer::AsUs() const {
-  return (clock_.now() - start_) / std::chrono::microseconds(1);
+  if (!is_started_) return 0.0;
+  const TimePoint end = ClockType::now();
+  return (end - start_) / std::chrono::microseconds(1);
 }
 }  // namespace metrics
 }  // namespace wvcdm