Add start/pause to Timer

src/timer.cc

@@ -10,33 +10,47 @@ Timer::Timer() {
 
 long long Timer::ElapsedMicroseconds() const {
   std::chrono::time_point<Clock> end = Clock::now();
-  return std::chrono::duration_cast<std::chrono::microseconds>(end - start)
-      .count();
+  long long elapsed = elapsed_;
+  if (start_.has_value()) {
+    // TODO: clang-format this file.
+    elapsed += std::chrono::duration_cast<std::chrono::microseconds>(end - *start_).count();
+  }
+  return elapsed;
 }
 
 long long Timer::ElapsedMicrosecondsAndReset() {
-  std::chrono::time_point<Clock> end = Clock::now();
-  long long microseconds =
-      std::chrono::duration_cast<std::chrono::microseconds>(end - start)
-          .count();
+  long long elapsed = ElapsedMicroseconds();
   Reset();
-  return microseconds;
+  return elapsed;
 }
 
 void Timer::Reset() {
-  start = Clock::now();
+  start_ = Clock::now();
+  elapsed_ = 0;
 }
 
 void Timer::ResetAndPrint(const std::string& message) {
-  std::chrono::time_point<Clock> end = Clock::now();
-  long long elapsed =
-      std::chrono::duration_cast<std::chrono::microseconds>(end - start)
-          .count();
-
+  long long elapsed = ElapsedMicroseconds();
   long long milliseconds = elapsed / 1000;
   long long remaining = elapsed - milliseconds;
-
   LOG_S(INFO) << message << " took " << milliseconds << "." << remaining
               << "ms";
   Reset();
 }
+
+void Timer::Pause() {
+  assert(start_.has_value());
+
+  std::chrono::time_point<Clock> end = Clock::now();
+  long long elapsed =
+      std::chrono::duration_cast<std::chrono::microseconds>(end - *start_)
+          .count();
+
+  elapsed_ += elapsed;
+  start_ = nullopt;
+}
+
+void Timer::Resume() {
+  assert(!start_.has_value());
+  start_ = Clock::now();
+}

src/timer.h

@@ -1,8 +1,13 @@
 #pragma once
 
+#include <optional.h>
+
 #include <chrono>
 #include <string>
 
+using std::experimental::nullopt;
+using std::experimental::optional;
+
 struct Timer {
   using Clock = std::chrono::high_resolution_clock;
 
@@ -17,7 +22,13 @@ struct Timer {
   void Reset();
   // Resets timer and prints a message like "<foo> took 5ms"
   void ResetAndPrint(const std::string& message);
+  // Pause the timer.
+  void Pause();
+  // Resume the timer after it has been paused.
+  void Resume();
 
   // Raw start time.
-  std::chrono::time_point<Clock> start;
+  optional<std::chrono::time_point<Clock>> start_;
+  // Elapsed time.
+  long long elapsed_ = 0;
 };