common/ceph_time: introduce time_guard for RAII-styled timediff calculation

Signed-off-by: Radoslaw Zarzynski <[email protected]>

Author: rzarzynski

src/common/ceph_time.h

@@ -342,6 +342,23 @@ class coarse_mono_clock {
   }
 };
 
+// Please note time_guard is not thread safety -- multiple threads
+// updating same diff_accumulator can corrupt it.
+template <class ClockT = mono_clock>
+class time_guard {
+  const typename ClockT::time_point start;
+  timespan& diff_accumulator;
+
+public:
+  time_guard(timespan& diff_accumulator)
+    : start(ClockT::now()),
+      diff_accumulator(diff_accumulator) {
+  }
+  ~time_guard() {
+    diff_accumulator += ClockT::now() - start;
+  }
+};
+
 namespace time_detail {
 // So that our subtractions produce negative spans rather than
 // arithmetic underflow.