Firestore C++: in AsyncQueue, use steady_clock instead of system_clock. (#1246)

This should prevent weird bugs due to system time readjustments. Because
operations are scheduled relative to now, the fact that the resulting
timepoint isn't in Unix epoch shouldn't matter.

3 files changed, 4 insertions, 4 deletions

diff --git a/Firestore/core/src/firebase/firestore/util/executor_libdispatch.mm b/Firestore/core/src/firebase/firestore/util/executor_libdispatch.mm
index b40f0dd..5491fec 100644
--- a/Firestore/core/src/firebase/firestore/util/executor_libdispatch.mm
+++ b/Firestore/core/src/firebase/firestore/util/executor_libdispatch.mm
@@ -109,7 +109,7 @@ class TimeSlot {
   void Execute();
   void RemoveFromSchedule();
 
-  using TimePoint = std::chrono::time_point<std::chrono::system_clock,
+  using TimePoint = std::chrono::time_point<std::chrono::steady_clock,
                                             Executor::Milliseconds>;
 
   ExecutorLibdispatch* const executor_;
@@ -129,7 +129,7 @@ TimeSlot::TimeSlot(ExecutorLibdispatch* const executor,
                    Executor::TaggedOperation&& operation)
     : executor_{executor},
       target_time_{std::chrono::time_point_cast<Executor::Milliseconds>(
-                       std::chrono::system_clock::now()) +
+                       std::chrono::steady_clock::now()) +
                    delay},
       tagged_{std::move(operation)} {
 }
diff --git a/Firestore/core/src/firebase/firestore/util/executor_std.cc b/Firestore/core/src/firebase/firestore/util/executor_std.cc
index 59197e1..f03a712 100644
--- a/Firestore/core/src/firebase/firestore/util/executor_std.cc
+++ b/Firestore/core/src/firebase/firestore/util/executor_std.cc
@@ -68,7 +68,7 @@ DelayedOperation ExecutorStd::Schedule(const Milliseconds delay,
                           "Schedule: delay cannot be negative");
 
   namespace chr = std::chrono;
-  const auto now = chr::time_point_cast<Milliseconds>(chr::system_clock::now());
+  const auto now = chr::time_point_cast<Milliseconds>(chr::steady_clock::now());
   const auto id =
       PushOnSchedule(std::move(tagged.operation), now + delay, tagged.tag);
 
diff --git a/Firestore/core/src/firebase/firestore/util/executor_std.h b/Firestore/core/src/firebase/firestore/util/executor_std.h
index 4ac62e1..58ef96f 100644
--- a/Firestore/core/src/firebase/firestore/util/executor_std.h
+++ b/Firestore/core/src/firebase/firestore/util/executor_std.h
@@ -55,7 +55,7 @@ class Schedule {
   // - each operation modifying the queue notifies the condition variable `cv_`.
  public:
   using Duration = std::chrono::milliseconds;
-  using Clock = std::chrono::system_clock;
+  using Clock = std::chrono::steady_clock;
   // Entries are scheduled using absolute time.
   using TimePoint = std::chrono::time_point<Clock, Duration>;