NSPR defines a platform-dependent type, {ref}`PRIntervalTime`, for timing
intervals of fewer than approximately 6 hours. This chapter describes
{ref}`PRIntervalTime` and the functions that allow you to use it for timing
purposes:

- [Interval Time Type and
  Constants](#Interval_Time_Type_and_Constants)
- [Interval Functions](#Interval_Functions)

(interval-time-type-and-constants)=

# Interval Time Type and Constants

All timed functions in NSPR require a parameter that depicts the amount
of time allowed to elapse before the operation is declared failed. The
type of such arguments is {ref}`PRIntervalTime`. Such parameters are common
in NSPR functions such as those used for I/O operations and operations
on condition variables.

NSPR 2.0 provides interval times that are efficient in terms of
performance and storage requirements. Conceptually, they are based on
free-running counters that increment at a fixed rate without possibility
of outside influence (as might be observed if one was using a
time-of-day clock that gets reset due to some administrative action).
The counters have no fixed epoch and have a finite period. To make use
of these counters, the application must declare a point in time, the
epoch, and an amount of time elapsed since that **epoch**, the
**interval**. In almost all cases the epoch is defined as the value of
the interval timer at the time it was sampled.

> - {ref}`PRIntervalTime`

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# Interval Functions

Interval timing functions are divided into three groups:

- [Getting the Current Interval and Ticks Per
  Second](#Getting_the_Current_Interval_and_Ticks_Per_Second)
- [Converting Standard Clock Units to Platform-Dependent
  Intervals](#Converting_Standard_Clock_Units_to_Platform-Dependent_Intervals)
- [Converting Platform-Dependent Intervals to Standard Clock
  Units](#Converting_Platform-Dependent_Intervals_to_Standard_Clock_Units)

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## Getting the Current Interval and Ticks Per Second

> - {ref}`PR_IntervalNow`
> - {ref}`PR_TicksPerSecond`

(converting-standard-clock-units-to-platform-dependent-intervals)=

## Converting Standard Clock Units to Platform-Dependent Intervals

> - {ref}`PR_SecondsToInterval`
> - {ref}`PR_MillisecondsToInterval`
> - {ref}`PR_MicrosecondsToInterval`

(converting-platform-dependent-intervals-to-standard-clock-units)=

## Converting Platform-Dependent Intervals to Standard Clock Units

> - {ref}`PR_IntervalToSeconds`
> - {ref}`PR_IntervalToMilliseconds`
> - {ref}`PR_IntervalToMicroseconds`