StatsdClient flush functionality

[James-Bartman]

Problem

The StatsDClient utilizes a MetricSink, which can optionally be buffered. Buffering helps save network bandwidth; however, the BufferedUdpMetricSink won't be flushed until it is full. For, an application which emits relatively few time-sensitive metrics in conjunction with a large amount of time-insensitive metrics, the default buffer flushing may not give the user enough control and result in faulty metric collection (especially since StatsD does not tag metics with a timestamp).

Solution

I have added a pub fn flush() to the StatsDClient which gives users the control they need to flush time-sensitive metrics while also allowing the regular buffer functionality to flush once the buffer is full. Also, I added a ToCounterValue implementation for the u64 type since most counters are unsigned.

[56quarters]

Hi! Thanks for the PR. Adding a flush() method to StatsdClient was previously proposed in #176. I'm still not a huge fan of adding that method and would rather have a sink that periodically flushes (every 1s or so) but it seems like people want this functionality.

I'm curious about your opinion @mlowicki since you recently made some flush() related changes to the QueuingMetricSink.

Also, I added a ToCounterValue implementation for the u64 type since most counters are unsigned.

Do you mind opening a separate PR for those changes? Thank you!

[James-Bartman]

Yeah we didn't see any sinks that flush on a time interval and also figured some manual control would be best for developers who need it. And sure, I will separate out the ToCounterValue changes. Thanks!

[mlowicki]

Hi! Thanks for the PR. Adding a flush() method to StatsdClient was previously proposed in #176. I'm still not a huge fan of adding that method and would rather have a sink that periodically flushes (every 1s or so) but it seems like people want this functionality.

I'm curious about your opinion @mlowicki since you recently made some flush() related changes to the QueuingMetricSink.

It should be still possible to manually flush by keeping reference to the underlying sink and calling flush() directly on such sink so method on StatsdClient seems redundant (although it may simplify the code by avoiding a bit of code to wrap the sink with Arc and so on).

[56quarters]

OK, I will defer to users instead of forcing everyone to copy the code from examples/wrapped.rs

[James-Bartman]

Sounds good, I've made the changes and everything should be RTG.

[56quarters]

One last change and I think this is good to merge.

[56quarters]

Thanks!