SERVER-36697 Utilize TickSource for transactions timing metrics

This patch converts the existing transactions diagnostics timing related
metrics to use a TickSource to record transaction durations. The
TickSource is a high precision, mock-able time source for measuring
the passage of time. This patch also converts the existing unit tests
to use a mock TickSource, which allows the tests to fully virtualize
time, making them much faster and less flaky.

1 files changed, 13 insertions, 0 deletions

diff --git a/src/mongo/util/tick_source.h b/src/mongo/util/tick_source.h
index 134f4d05737..1aef0e478dc 100644
--- a/src/mongo/util/tick_source.h
+++ b/src/mongo/util/tick_source.h
@@ -50,5 +50,18 @@ public:
      * Returns the conversion ratio from ticks to seconds.
      */
     virtual Tick getTicksPerSecond() = 0;
+
+    /**
+     * Convert the given tick count into a duration, specified by the type parameter.
+     *
+     * e.g. tickSource->ticksTo<Milliseconds>(ticks);
+     */
+    template <typename D>
+    D ticksTo(Tick ticks) {
+        // The number of ticks per 1 duration unit.
+        double ticksPerD =
+            static_cast<double>(getTicksPerSecond()) * D::period::num / D::period::den;
+        return D(static_cast<int64_t>(ticks / ticksPerD));
+    }
 };
 }  // namespace mongo