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I do not understand why we need to make this change to `Gauge`. It should
already now be possible to `defer` to the current thread, i.e., with no
additional `dispatch` cost, by using `process::defer(F&&)`.
If the test code you added would use a definition like
Gauge gaugeConst("test/gauge_const", process::defer([]() { return 99.;
}));
no other changes, e.g., to `Gauge`, would be required to make the tests pass.
This code does not involve runtime-dispatches, but instead creates a
`_Deferred` which is implicitly converted a `Deferred` in the construction of
the `Gauge`,
https://github.com/apache/mesos/blob/79daf9769d28317a7314b8c6e75cf18c0c293683/3rdparty/libprocess/include/process/deferred.hpp#L76-L78.
- Benjamin Bannier
On June 6, 2017, 11:16 p.m., James Peach wrote:
>
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> This is an automatically generated e-mail. To reply, visit:
> https://reviews.apache.org/r/59858/
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>
> (Updated June 6, 2017, 11:16 p.m.)
>
>
> Review request for mesos, Benjamin Bannier and Benjamin Mahler.
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> Repository: mesos
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>
> Description
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>
> 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/2/
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>
> Testing
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> make check (Fedora 25)
>
>
> Thanks,
>
> James Peach
>
>
