SERVER-13874 Support converting Date_t to system_clock::time_point and back.

3 files changed, 35 insertions, 3 deletions

diff --git a/src/mongo/util/time_support.cpp b/src/mongo/util/time_support.cpp
index 4c588d39071..57eefa80775 100644
--- a/src/mongo/util/time_support.cpp
+++ b/src/mongo/util/time_support.cpp
@@ -126,6 +126,13 @@ namespace {
         return fromMillisSinceEpoch(curTimeMillis64());
     }
 
+    Date_t::Date_t(stdx::chrono::system_clock::time_point tp) :
+        millis(durationCount<Milliseconds>(tp - stdx::chrono::system_clock::from_time_t(0))) {}
+
+    stdx::chrono::system_clock::time_point Date_t::toSystemTimePoint() const {
+        return stdx::chrono::system_clock::from_time_t(0) + toDurationSinceEpoch();
+    }
+
     bool Date_t::isFormattable() const {
         if (millis < 0) {
             return false;
diff --git a/src/mongo/util/time_support.h b/src/mongo/util/time_support.h
index 596812e4b65..3d5128f43e9 100644
--- a/src/mongo/util/time_support.h
+++ b/src/mongo/util/time_support.h
@@ -119,7 +119,12 @@ namespace mongo {
         /**
          * Constructs a Date_t representing the epoch.
          */
-        Date_t(): millis(0) {}
+        Date_t() = default;
+
+        /**
+         * Constructs a Date_t from a system clock time point.
+         */
+        explicit Date_t(stdx::chrono::system_clock::time_point tp);
 
         /**
          * Returns a string representation of the date.
@@ -165,6 +170,11 @@ namespace mongo {
          */
         long long toMillisSinceEpoch() const { return static_cast<long long>(millis); }
 
+        /*
+         * Returns a system clock time_point representing the same point in time as this Date_t.
+         */
+        stdx::chrono::system_clock::time_point toSystemTimePoint() const;
+
         /**
          * Returns true if this Date_t is in the range of Date_ts that can be formatted as calendar
          * dates.  This property is guaranteed to be true for all dates from the epoch,
@@ -173,6 +183,12 @@ namespace mongo {
          */
         bool isFormattable() const;
 
+        /**
+         * Implicit conversion operator to system clock time point.  Enables use of Date_t with
+         * condition_variable::wait_until.
+         */
+        operator stdx::chrono::system_clock::time_point () const { return toSystemTimePoint(); }
+
         template <typename Duration>
         Date_t& operator+=(Duration d) {
             millis += duration_cast<Milliseconds>(d).count();
@@ -223,9 +239,9 @@ namespace mongo {
         }
 
     private:
-        Date_t(long long m): millis(m) {}
+        explicit Date_t(long long m): millis(m) {}
 
-        long long millis;
+        long long millis = 0;
     };
 
     // uses ISO 8601 dates without trailing Z
diff --git a/src/mongo/util/time_support_test.cpp b/src/mongo/util/time_support_test.cpp
index 8c8f1a74f37..22a97acaf13 100644
--- a/src/mongo/util/time_support_test.cpp
+++ b/src/mongo/util/time_support_test.cpp
@@ -825,5 +825,14 @@ namespace {
         ASSERT_EQUALS("52ms52\xce\xbcs52s", os.str());
     }
 
+    TEST(SystemTime, ConvertDateToSystemTime) {
+        const std::string isoTimeString = "2015-05-14T17:28:33.123Z";
+        const Date_t aDate = unittest::assertGet(dateFromISOString(isoTimeString));
+        const auto aTimePoint = aDate.toSystemTimePoint();
+        ASSERT_EQUALS(aDate.toDurationSinceEpoch(),
+                      aTimePoint - stdx::chrono::system_clock::from_time_t(0));
+        ASSERT_EQUALS(aDate, Date_t(aTimePoint));
+    }
+
 }  // namespace
 }  // namespace mongo