Re: [Tarantool-patches] [PATCH 2/2] app/fiber: wait till a full event loop iteration ends.

[Vladislav Shpilevoy <v.shpilevoy@tarantool.org>]

Hi! Thanks for the path!

We don't use dots in commit title. I guess this is a typo.

On 13/11/2019 19:04, Serge Petrenko wrote:
> fiber.top() fills in statistics every event loop iteration,
> so if it was just enabled, fiber.top() may contain 'inf's and
> 'nan's in fiber cpu usage averages because total time consumed by
> the main thread was not yet accounted for.
> Same stands for viewing top() results for a freshly created fiber:
> its metrics will be zero since it hasn't lived a full ev loop iteration
> yet.
> Fix this by delaying the test till top() results are meaningful and add
> minor refactoring.
> 
> Follow-up #2694
> ---
>  test/app/fiber.result   | 35 ++++++++++++++++++++++++++---------
>  test/app/fiber.test.lua | 31 +++++++++++++++++++++++--------
>  2 files changed, 49 insertions(+), 17 deletions(-)
> 
> diff --git a/test/app/fiber.result b/test/app/fiber.result
> index 4a094939f..d447a36fc 100644
> --- a/test/app/fiber.result
> +++ b/test/app/fiber.result
> @@ -1469,6 +1469,19 @@ sum = 0
>  fiber.top_enable()
>  ---
>  ...
> +-- Check that a number is finite.
> +-- Lua doesn't have this, sorry.
> +function finite(num)\
> +    return type(num) == 'number' and num < math.huge and\
> +           num > -math.huge and tostring(num) ~= 'nan'\

1. A canonical way to check for NaN is compare a value with
itself. If they are not equal, then it is NaN.

But more important questions are:
- How can a number from top() have a not 'number' type?
- How can top() contain a NaN, and an infinite value?

> +end
> +---
> +...
> +-- Wait till a full event loop iteration passes, so that
> +-- top() contains meaningful results.
> +while not finite(fiber.top().cpu["1/sched"].instant) do  fiber.yield() end

2. Double whitespace after 'do'.