Review Videos! • clocks, clock_cast, leap_seconds (https://youtu.be/WX3OmVu4lAs) • time_zone and time_zone_link (https://youtu.be/MODhhr7m-5s) • system_clock::now(), file_clock, leap second awareness (https://youtu 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 { public: is_steady = false; static time_point now() {} }; static_assert(is_clock_v); For a type T to qualify as a Clock, it must satisfy each of the following conditions: • The following qualified-ids

in :  std::system_clock: wall clock time from system-wide real-time clock  std::steady_clock: guarantees it never goes backwards  std::high_resolution_clock: has shortest possible tick C++20 adds:  utc_clock, tai_clock, gps_clock, and file_clock  Every clock has a now() method21 Clocks – Examples  Example: // Get current time as a time_point. system_clock::time_point tpoint tpoint { system_clock::now() }; // Or: auto tpoint { system_clock::now() }; // Convert to a time_t. time_t tt { system_clock::to_time_t(tpoint) }; // Convert to local time. tm* t { localtime(&tt) }; // Write

uint64_t CPU_CLOCK_HZ = 400'000'000; // API to implement: std::chrono::nanoseconds elapsed_time(uint64_t num_cpu_ticks); 1 2 3 4 8Example: “CPU ticks” time units constexpr uint64_t CPU_CLOCK_HZ = 400'000'000; nds elapsed_time(uint64_t num_cpu_ticks) { using NS_PER_TICK = std::ratio<1'000'000'000, CPU_CLOCK_HZ>; return std::chrono::nanoseconds{ num_cpu_ticks * NS_PER_TICK::num / NS_PER_TICK::den NS_PER_TICK::den }; } 1 2 3 4 5 6 8.1Example: “CPU ticks” time units constexpr uint64_t CPU_CLOCK_HZ = 400'000'000; // API to implement: std::chrono::nanoseconds elapsed_time(uint64_t num_cpu_ticks); 1 2

also passes. Finally, TiDB has a theoretical dependence on CLOCK_MONOTONIC_RAW for safety, but we have not yet observed anomalies due to clock skew, possibly due to tooling limitations. PingCAP has published are some 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 shouldn’t result in prolonged un- availability: PD will allocate timestamps in the future if its own clock falls behind what’s committed to Raft. To improve throughput, PD nodes reserve a batch of timestamps

(int i { startValue }; i < startValue + numberOfValues; ++i) { time_t t { system_clock::to_time_t(system_clock::now()) }; cout << std::ctime(&t); co_yield i; } } int main() { auto gen 1 week into days62 Calendars & Timezones  New clocks (besides system_clock, steady_clock, high_resolution_clock):  utc_clock: represents Coordinated Universal Time (UTC), measures time since 00:00:00 00:00:00 UTC, Thursday, 1 January 1970, including leap seconds  tai_clock: represents International Atomic Time (TAI), measures time since 00:00:00, 1 January 1958, and was offseted 10 seconds ahead of

auto start = Clock::now(); for( size_t i=0; iconcrete(); } auto end = Clock::now(); auto concrete_duration = end-start; start = Clock::now(); for( for( size_t i=0; ivirt(); } end = Clock::now(); auto virt_duration = end-start;There are interesting technical details and surprising conclusions that virtual

. . . . . . . . . . . . . . . . . . . . . . . . . . 159 9.13.2 Accelerate or slow down the guest clock . . . . . . . . . . . . . . . . . . 160 9.13.3 Tuning the Guest Additions time synchronization parameters details. Hardware clock in UTC time If checked, VirtualBox will report the system time in UTC format to the guest instead of local (host) time. This affects how the virtual real-time clock (RTC) operates operates and may be useful for Unix-like guest operating systems, which typically expect the hardware clock to be set to UTC. Enable absolute pointing device If enabled, VirtualBox reports to the virtual machine

. . . . . . . . . . . . . . . . . . . . . . . . . . 170 9.15.2 Accelerate or slow down the guest clock . . . . . . . . . . . . . . . . . . 171 9.15.3 Tuning the Guest Additions time synchronization parameters details. Hardware clock in UTC time If checked, VirtualBox will report the system time in UTC format to the guest instead of local (host) time. This affects how the virtual real-time clock (RTC) operates operates and may be useful for Unix-like guest operating systems, which typically expect the hardware clock to be set to UTC. Enable absolute pointing device If enabled, VirtualBox reports to the virtual machine

above: async def minute_loop2(): while True: nxt = gen.sleep(60) # Start the clock. await do_something() # Run while the clock is ticking. await nxt # Wait for the timer to run out. 6.1.4 Queue example request. • start_time: Time at which the HTTP operation started, based on time.time (not the monotonic clock used by IOLoop.time). May be None if the request timed out while in the queue. • time_info: dictionary implementa- tions. request_time is now more accurate for curl_httpclient because it uses a monotonic clock when available. rethrow() → None If there was an error on the request, raise an HTTPError. Exceptions

in the Game Boy's CPU, typically corresponding to one clock tick of the CPU. Emulators with T-cycle accuracy simulate the exact number of clock ticks for every instruction, providing the highest level in the Game Boy's CPU, typically corresponding to one clock tick of the CPU. Emulators with T-cycle accuracy simulate the exact number of clock ticks for every instruction, providing the highest level