Added a util scope timer class

Signed-off-by: Thien Nguyen <nguyentm@ornl.gov>

xacc/utils/Utils.cpp

@@ -310,4 +310,25 @@ void XACCLogger::error(const std::string &msg, MessagePredicate predicate) {
   }
 }
 
+ScopeTimer::ScopeTimer(const std::string& scopeName, bool shouldLog):
+  m_startTime(std::chrono::system_clock::now()),
+  m_shouldLog(shouldLog),
+  m_scopeName(scopeName)
+  {
+    if (m_shouldLog) {
+      XACCLogger::instance()->info("'" + scopeName + "' started.");
+    }
+  }
+
+double ScopeTimer::getDurationMs() const {
+  return static_cast<double>(
+    std::chrono::duration_cast<std::chrono::microseconds>(std::chrono::system_clock::now() - m_startTime).count()/1000.0);
+}
+
+ScopeTimer::~ScopeTimer() {
+  const double elapsedTime = getDurationMs();
+  if (m_shouldLog) {
+    XACCLogger::instance()->info("'" + m_scopeName + "' finished [" + std::to_string(elapsedTime) + " ms].");
+  }
+}
 } // namespace xacc

xacc/utils/Utils.hpp

@@ -21,6 +21,7 @@
 #include <sstream>
 #include <algorithm>
 #include <map>
+#include <chrono>
 
 namespace spdlog {
 class logger;
@@ -233,6 +234,40 @@ template <typename T> std::vector<T> linspace(T a, T b, size_t N) {
   return xs;
 }
 
+// Util timer to log execution elapsed time of a scope block.
+// Example usage:
+// (1) Time a function body:
+/* 
+void slowFunc {
+  // Use __FUNCTION__ macro to get the function name 
+  // Can use a custom string as well
+  ScopeTimer timer(__FUNCTION__);
+  .... code
+}
+*/
+// The above timer will log when the function starts and ends (with elapsed time).
+// (2) Time a code block, including function calls
+/* 
+ ... irrelevant code
+ // Create a scope block:
+ {
+  ScopeTimer timer("human readable name of this block");
+  .... code
+ }
+  ... irrelevant code
+*/
+// This will log the timing data of that specific code block.
+class ScopeTimer {
+public:
+  ScopeTimer(const std::string& scopeName, bool shouldLog = true);
+  double getDurationMs() const;
+  ~ScopeTimer();
+private:
+  std::chrono::time_point<std::chrono::system_clock> m_startTime;
+  bool m_shouldLog;
+  std::string m_scopeName;
+};
+
 // container helper
 namespace container {
   template<typename ContainerType, typename ElementType>