Navigation :

Time Methods

Introduction

The Lua language does not provide a native high-resolution time function.

These supplementary time-based methods are provided for convenience and compatibility.

These methods are accessed via the “n2.n2svcd” module:

    local n2svcd = require "n2.n2svcd"

.wait [Asynchronous]

This method sets a timer and hands control back to the LogicApp. When the timer expires the Lua script will be resumed.

The wait method takes the following parameters.

Parameter	Type	Description
`seconds`	Number	The number of seconds to wait.

Example:

    n2svcd.wait (5)

The wait method returns true.

.time [Synchronous]

The time method takes no parameters.

The time method returns a floating point “epoch” seconds.

This is more efficient and easier to use than the gettimeofday methods, since time deltas can be computed with a simple subtraction or addition.

    local start_time = n2svcd.time ()

    -- Processing occurs here.

    local end_time = n2svcd.time ()
    local elapsed_seconds = end_time - start_time

    if (elapsed_seconds > 0.5) then
        error ("Processing too slow.  Aborting script!")
    end

.gettimeofday [Synchronous]

The get_time_of_day method takes no parameters.

The get_time_of_day method returns a two-element Lua list.

Parameter	Type	Description
`[1]`	Integer	The total number of Epoch seconds.
`[2]`	Integer	The microseconds associated with our number of Epoch seconds.

    local tod = n2svcd.gettimeofday ()
    n2svcd.debug ("NOW = %d.%d", tod[1], tod[2])

.get_time_of_day [Synchronous]

The get_time_of_day method is a minor variant which returns a Lua table with named attributes.

Parameter	Type	Description
`seconds`	Integer	The total number of Epoch seconds.
`microseconds`	Integer	The microseconds associated with our number of Epoch seconds.

    local tod = n2svcd.get_time_of_day ()
    n2svcd.debug ("NOW = %d.%d", tod.seconds, tod.microseconds)

.tv_interval [Pure Lua]

The tv_interval method accepts either one or two two-element Lua lists as returned from gettimeofday.

Parameter	Type	Description
`from`	Two-Element Integer List	[Required] The start time of the interval.
`to`	Two-Element Integer List	The end time of the interval. (Default: The current time "now")

The tv_interval method returns the floating-point number difference in seconds between the times represented by from and to. If the from time is later than the to time then the result will be negative.

    local from = n2svcd.gettimeofday ()
    n2svcd.wait (3.5)
    local to = n2svcd.gettimeofday ()
    n2svcd.debug ("ELAPSED = %f", n2svcd.tv_interval (from, to))