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From James Peach <jpe...@apache.org>
Subject Re: Review Request 59858: Allow Gauge metrics to avoid process::defer().
Date Tue, 06 Jun 2017 23:31:52 GMT


> On June 6, 2017, 10:18 p.m., Benjamin Bannier wrote:
> > 3rdparty/libprocess/include/process/metrics/gauge.hpp
> > Line 34 (original), 35-39 (patched)
> > <https://reviews.apache.org/r/59858/diff/2/?file=1743153#file1743153line35>
> >
> >     I believe the gist of this change is to recognize that a `Gauge` has no dependency
on the production of its value to be deferred; instead this decision should be should be left
to the creator of the `Gauge`.
> >     
> >     For most existing `Gauge`s in the Mesos code base we not only depend on some
process to carry out calculcation of values, but also introduce a life-time dependency made
safe by using `Deferred`. This is inherent to the functions passed in here (they could e.g.,
be implicitly converted from a `_Deferred`.
> >     
> >     Given that, I am not sure we need to explain `Deferred` here. I would instead
update the existing comment, e.g., `s/deferred object/producer function/` or similar.

I wanted to capture something about the common usage in the codebase and give some guidance
without second-guessing how this should be used. I would like to make the comment a bit more
expansive so we can explain how to use `Gauge` safely, but I'm open to suggestions :)


- James


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https://reviews.apache.org/r/59858/#review177103
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On June 6, 2017, 9:16 p.m., James Peach wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://reviews.apache.org/r/59858/
> -----------------------------------------------------------
> 
> (Updated June 6, 2017, 9:16 p.m.)
> 
> 
> Review request for mesos, Benjamin Bannier and Benjamin Mahler.
> 
> 
> Repository: mesos
> 
> 
> Description
> -------
> 
> A `Deferred` function object is always defined to be a
> `std::function`, so when we are constructing a `Gauge` metrics
> is it not strictly required for the callback to be a `Deferred`
> object. In cases where the value is a constant or can be calculated
> by reading constant data, a metrics producer can emit a `Gauge`
> without the taking the additional dispatch cost.
> 
> 
> Diffs
> -----
> 
>   3rdparty/libprocess/include/process/metrics/gauge.hpp c5bbeaf5d53c60f3636d1778db47cdb6cdda34e8

>   3rdparty/libprocess/src/tests/metrics_tests.cpp c13520d23ca17144f553fb4588fb8a747ea46e72

> 
> 
> Diff: https://reviews.apache.org/r/59858/diff/3/
> 
> 
> Testing
> -------
> 
> make check (Fedora 25)
> 
> 
> Thanks,
> 
> James Peach
> 
>


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