How deeply does 100 Go Mistakes and How to Avoid Them cover clock?

Distinguishes wall and monotonic clocks, traces JSON’s loss of monotonic data, and contrasts == with Equal.

Clock

As explained in 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.

A wall clock represents the current time of day, but synchronization such as NTP can make it jump forward or backward. Do not measure durations with it: backward jumps can produce negative durations. A monotonic clock instead moves forward continuously and is not affected by time jumps. section 10.3.2

When JSON changes a time comparison

Calling time.Now() can produce a time.Time containing both wall and monotonic time. JSON preserves the wall time but drops the monotonic value, so comparing the original and unmarshaled structs with == prints false even though they represent the same instant. Use time.Time.Equal for instant comparison, or remove the monotonic component with Truncate(0) before a structural comparison.

Choose the operation according to what the timestamp means:

Use the wall time to represent calendar or clock time, including values serialized through JSON. section 10.3.2
Use a monotonic clock for elapsed-time measurement when clock synchronization could otherwise distort the result. section 10.3.2
Use Equal instead of == when comparing time.Time values that may have different monotonic components. section 10.8

How 100 Go Mistakes and How to Avoid Them covers it

Cover of 100 Go Mistakes and How to Avoid Them

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Also explained in

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Rust in Action: Systems programming concepts and techniquesA system clock is the operating system's maintained representation of the current time, from which applications obtain time values.
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Acing the CCNA Exam: Volume 2 Advanced Networking and SecurityA software clock is the operating-system-maintained clock in a network device that tracks the current date and time.
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C++ Concurrency in Action, Second EditionA 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.
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Modern Cclock is a C standard library function that obtains processor time consumed by the program.

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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.

This explainer was generated by Manning's knowledge graph from the text of 100 Go Mistakes and How to Avoid Them. The section links point to the parts of the book it draws on.