Process • Implementing in the Open • Organization of Work • Part II: Calendrical Types • Part III: Clocks • Part IV: Leap Seconds • What are leap seconds? • How did we implement them in MSVC? • Part Feature branch (feature/chrono) for rapid development and collaboration • Code Review Videos! • clocks, clock_cast, leap_seconds (https://youtu.be/WX3OmVu4lAs) • time_zone and time_zone_link (https://youtu clients of them! Plus, the types often end up boiling down to constants anyway!18 Part III: Clocks19 What is a clock? #include #include using namespace std::chrono; class MyClock

Compile-Time Rational Numbers  Durations  Clocks  Time Points  Dates  Time Zones 4 Agenda  Compile-Time Rational Numbers  Durations  Clocks  Time Points  Dates  Time Zones5 = ratio<1'000'000'000'000'000'000, 1>;9 Agenda  Compile-Time Rational Numbers  Durations  Clocks  Time Points  Dates  Time Zones10 Durations  Interval between two points in time  Represented // 1.519 Agenda  Compile-Time Rational Numbers  Durations  Clocks  Time Points  Dates  Time Zones20 Clocks  Several clocks available in :  std::system_clock: wall clock time from

wall-clock dependencies in TiDB. Placement Driver, for instance, allocates timestamps based on local wall-clocks, but ensures monotonicity through Raft plus a leader lease. Clock skew between PD nodes can cause strobing the clock up and down ev- ery few milliseconds. We also used libfaketime to simulate some node clocks, both CLOCK_REALTIME and CLOCK_MONOTONIC, running up to 5x faster than oth- ers. PingCAP had written increas- ing. PingCAP and Jepsen believe this could lead to consistency anomalies when monotonic clocks are not well behaved. However, we don’t have experimental ev- idence to confirm this hypothesis.

make a copy of the underlying data ambiguous [‘infer’, bool-ndarray, ‘NaT’, default ‘raise’] When clocks moved backward due to DST, ambiguous times may arise. For example in Central European Time (UTC+01) nonexistent [str, default ‘raise’] A nonexistent time does not exist in a particular timezone where clocks moved forward due to DST. Valid valuse are: • ‘shift_forward’ will shift the nonexistent time forward information preserving local time. ambiguous [‘infer’, ‘NaT’, bool array, default ‘raise’] When clocks moved backward due to DST, ambiguous times may arise. For example in Central European Time (UTC+01)

daylight savings time (DST) in a local time zone causes some times to occur twice within one day (“clocks fall back”). The following options are available: • 'raise': Raises a pytz.AmbiguousTimeError (the A DST transition may also shift the local time ahead by 1 hour creating nonexistent local times (“clocks spring forward”). The behavior of localizing a timeseries with nonexistent times can be controlled make a copy of the underlying data. ambiguous [‘infer’, bool-ndarray, ‘NaT’, default ‘raise’] When clocks moved back- ward due to DST, ambiguous times may arise. For example in Central European Time (UTC+01)

daylight savings time (DST) in a local time zone causes some times to occur twice within one day (“clocks fall back”). The following options are available: • 'raise': Raises a pytz.AmbiguousTimeError (the A DST transition may also shift the local time ahead by 1 hour creating nonexistent local times (“clocks spring forward”). The behavior of localizing a timeseries with nonexistent times can be controlled make a copy of the underlying data ambiguous [‘infer’, bool-ndarray, ‘NaT’, default ‘raise’] When clocks moved backward due to DST, ambiguous times may arise. For example in Central European Time (UTC+01)

daylight savings time (DST) in a local time zone causes some times to occur twice within one day (“clocks fall back”). The following options are available: • 'raise': Raises a pytz.AmbiguousTimeError (the A DST transition may also shift the local time ahead by 1 hour creating nonexistent local times (“clocks spring forward”). The behavior of localizing a timeseries with nonexistent times can be controlled make a copy of the underlying data ambiguous [‘infer’, bool-ndarray, ‘NaT’, default ‘raise’] When clocks moved backward due to DST, ambiguous times may arise. For example in Central European Time (UTC+01)

University 2020 1. Watermarks must be monotonically increasing in order to ensure that the event time clocks of tasks are progressing and not going backwards. 2. A watermark with a timestamp T indicates that

Google discarded the NTP in favor of its own time-keeping mechanism ● TrueTime API ○ Atomic clocks ○ GPS (global positioning system) receivers Google F1 ● ○ ○ ○ ○ ● ○ ○ ○ ○ ○ Let’s talk about

QoS policy ● Timer -- periodical notification/callback ● Time/Time Source -- different type of clocks ● Actionlib w/ RethinkRobotics* -- preemptable task management ● Message Gen (idl) -- dynamic