Timespecs

Timespecs refer to time specifications used in computing to represent a moment in time or a time interval with nanosecond precision. They are a core concept in POSIX and related APIs, where a timespec is a small data structure used to pass high-resolution time values between user space and the kernel or between library functions.

The standard representation is a struct timespec, defined in time.h. It typically contains two fields: time_t tv_sec, which holds whole seconds, and long tv_nsec, which holds the nanoseconds part of the time. The combination of tv_sec and tv_nsec identifies a point in time or an elapsed duration, with tv_nsec always in the range 0 to 999,999,999.

Timespec-based values are produced or consumed by several APIs. clock_gettime returns the current time for a given clock as a timespec. nanosleep suspends execution for a duration specified by a timespec. Timers and event sources in POSIX use timespec to define periods, deadlines, and timeouts.

Portability and variants: While timespec is standard in POSIX, there are platform differences in size and range of fields, particularly for time_t and long. Some systems provide a 64-bit variant, such as timespec64, to maintain compatibility with 32-bit time representations. The general concept remains a two-field representation of seconds and nanoseconds, enabling high-resolution time measurements and precise timeouts across compatible systems. Usage in practice includes high-resolution timing, performance measurement, and fine-grained scheduling in POSIX-compliant environments.