SERVER-45857 Add time measurement class to ClockSource

This commit adds the mongo::ClockSource::StopWatch class.

2 files changed, 44 insertions, 0 deletions

diff --git a/src/mongo/util/clock_source.cpp b/src/mongo/util/clock_source.cpp
index 00f1a6d32c5..7fa1eb32e66 100644
--- a/src/mongo/util/clock_source.cpp
+++ b/src/mongo/util/clock_source.cpp
@@ -98,4 +98,7 @@ stdx::cv_status ClockSource::waitForConditionUntil(stdx::condition_variable& cv,
     alarmInfo->cv = nullptr;
     return alarmInfo->result;
 }
+
+ClockSource::StopWatch::StopWatch() : StopWatch(SystemClockSource::get()){};
+
 }  // namespace mongo
diff --git a/src/mongo/util/clock_source.h b/src/mongo/util/clock_source.h
index f202f67f439..f57c2a35200 100644
--- a/src/mongo/util/clock_source.h
+++ b/src/mongo/util/clock_source.h
@@ -58,6 +58,40 @@ class ClockSource {
     static constexpr auto kMaxTimeoutForArtificialClocks = Seconds(1);
 
 public:
+    /**
+     * A StopWatch tracks the time that its ClockSource believes has passed since the creation of
+     * the StopWatch.
+     *
+     * For microsecond accurate metrics, use a Timer instead.
+     */
+    class StopWatch {
+    public:
+        StopWatch(ClockSource* clockSource, Date_t start)
+            : _clockSource{clockSource}, _start{start} {}
+        StopWatch(ClockSource* clockSource) : StopWatch(clockSource, clockSource->now()) {}
+        StopWatch(/** SystemClockSource::get() */);
+
+        Date_t now() noexcept {
+            return _clockSource->now();
+        }
+
+        ClockSource* getClockSource() noexcept {
+            return _clockSource;
+        }
+
+        auto start() const noexcept {
+            return _start;
+        }
+
+        auto elapsed() noexcept {
+            return now() - _start;
+        }
+
+    private:
+        ClockSource* const _clockSource;
+        const Date_t _start;
+    };
+
     virtual ~ClockSource() = default;
 
     /**
@@ -138,6 +172,13 @@ public:
         return waitForConditionUntil(cv, m, now() + duration, pred, waitable);
     }
 
+    /**
+     * Return a StopWatch that uses this ClockSource to track time
+     */
+    StopWatch makeStopWatch() {
+        return StopWatch(this);
+    }
+
 protected:
     bool _tracksSystemClock = true;
 };