Clock
A computer clock is a timekeeping source or interface that provides time values or measurements to software.
Rust in Action: Systems programming concepts and techniques
A system clock is the operating system's maintained representation of the current time, from which applications obtain time values.
- How it is used
- Provides the operating system’s current-time values to applications and serves as the clock adjusted during time synchronization.
- How deep it goes
- Defines the clock, explains its hardware relationship and jumps, and outlines OS-specific setting; the shown libc call omits success checking.
- Examples
- Uses a Raspberry Pi starting at the epoch and a Rust libc::settimeofday implementation to make clock behavior concrete.
- What you can do after
- Build it from scratch: create an NTP client and set system time through OS-specific calls while accounting for clock jumps.
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Acing the CCNA Exam: Volume 2 Advanced Networking and Security
A software clock is the operating-system-maintained clock in a network device that tracks the current date and time.
- How it is used
- Supports accurate timestamps for security mechanisms, log correlation, troubleshooting, and network-device operation.
- How deep it goes
- Defines software and hardware clocks, supplies IOS commands, and verifies NTP synchronization with operational output.
- Examples
- Uses show clock detail, clock set, calendar set, clock timezone, and NTP association and status outputs.
- What you can do after
- Operate/configure a Cisco device clock, synchronize it with NTP, and verify its source, authority, and synchronization state.
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C++ Concurrency in Action, Second Edition
A C++ chrono clock is a class that provides a time source, a time-point type, a tick period, and information about whether it is steady.
- How it is used
- Supplies time readings for measuring elapsed work and calculating deadlines or timeouts.
- How deep it goes
- Defines clock properties, time-point relationships, and arithmetic, while noting that epochs are not directly queryable.
- Examples
- Uses system_clock::now(), a 500-nanosecond offset, and high_resolution_clock readings to illustrate clock use.
- What you can do after
- Apply std::chrono to read clock values, measure elapsed time, and calculate time-based deadlines.
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Modern C
clock is a C standard library function that obtains processor time consumed by the program.
- How it is used
- Measures processor time consumed by the running program.
- How deep it goes
- Defines the function's purpose and prototype but does not explain timing units or conversion.
- Examples
- Shows the declaration clock_t clock(void).
- What you can do after
- Evaluate processor time consumed by a program using clock.
100 Go Mistakes and How to Avoid Them
A wall clock is a clock that represents the current time of day and may jump forward or backward when synchronized.
- How it is used
- Explains why wall-clock jumps and JSON round trips can produce surprising time behavior in Go programs.
- How deep it goes
- Distinguishes wall and monotonic clocks, traces JSON’s loss of monotonic data, and contrasts == with Equal.
- Examples
- Uses a time.Time JSON round trip, printed monotonic data, Equal, and Truncate(0) to expose comparison differences.
- What you can do after
- Diagnose misleading time.Time comparisons and choose Equal, Truncate(0), or monotonic timing appropriately.
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Related concepts
- nowuses · A now operation or keyword yields or derives a value representing the current date or time according to a relevant clock or system.
- time_pointconfigured by · std::chrono::time_point is a C++ standard library class template representing a point in time relative to a clock's epoch, measured using a duration.
- NTPconfigured by · The Network Time Protocol is an Internet protocol that synchronizes computer clocks over packet-switched networks using reference time sources and timestamp exchanges.
- monotonic clockcontrasts with · A monotonic clock is a time source whose readings never decrease and are suitable for measuring elapsed durations independently of wall-clock adjustments.
- system_clockincludes · std::chrono::system_clock is a C++ standard-library clock that represents system-wide wall-clock time and can be converted to and from calendar time.
- timestampproduces · A timestamp is a value representing a specific point in time, typically associated with an event, observation, or data item.
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