Add a new Gauge class ValueGauge

[comcastrong]

Hey,
I added a new Gauge class ValueGauge class which can save any gauge value as a long number. Somebody else might need use it. Can you please review it and pull merge to your master? If you have any questions, please let me know. My email is : yongjun_rong@cable.comcast.com
Thank you.
Yongjun Rong

[codahale]

This doesn't merge cleanly, but it's also not broadly applicable to most usages of Metrics. Returning a constant value doesn't need much in the way of optimization.

[comcastrong]

ok. I also fixed this issue mojodna/metricsd#2 by adding the new ValueGauge class. By the way, what do you mean optimization here? Do you mean most people prefer to use the RatioGauge, PercentGauge?

[codahale]

I mean, it's optimizing the following code:

new Gauge<Long>() {
    @Override
    public Long value() {
        return 33;
    }
};

You're the first person to want to do this, so unless other people speak up about this I'm not going to add more complexity to Metrics.

[comcastrong]

That way cannot get the latest gauge value. Please refer to mojodna/metricsd#2 . In MetricsRegistry,

public <T> Gauge<T> newGauge(MetricName metricName,
                                 Gauge<T> metric) {
        return getOrAdd(metricName, metric);
    }

It will return the first metric always. The metrics value never get changed.

[codahale]

I know.

The gauge is responsible for returning the most recent value. This is not the responsibility of the registry.

[comcastrong]

The gauge itself cannot reset the value to a new value if there is way to change the value inside the existing gauge in the registry. That's why I have to add this to the class Metrics

/**
     * Given a new gauge Long value, registers it under the given metric name.
     *
     * @param metricName the name of the metric
     * @param value    the gauge value
     * @return {@code ValueGauge}
     */
    public static ValueGauge newGauge(MetricName metricName,
                                        Long metricValue) {

        ValueGauge gauge = (ValueGauge) DEFAULT_REGISTRY.newGauge(metricName, new ValueGauge());
        gauge.set(metricValue);
        return gauge;
    }

[codahale]

Ok, I'm not sure what problem you're trying to solve. The issue you're linking to seems unrelated to the code you're posting.

If you want a mutable gauge, make a mutable gauge in your own application. I will not accept this patch.

[comcastrong]

It's your decision. The issue I linked to is not related. I miss understood it. The problem I'm trying to solve is that the gauge registered in the MetricsRegistry should be able to change the value from outside. If it use the optimization way you provided to instantiate a new gauge instance by override the value method. The gauge value in the MetricsRegistry never get changed because it always returns the first gauge instance with the first gauge value.
Thanks
Yongjun Rong

[comcastrong]

Another question, we found in metrics, it will attach ".value" for gauge and ".count" for counter in the end of the graphite stats scheme name. Like for example, when sending in "jmx.test", it will show up as "jmx.test.count" in graphite after it pass through the metrics. Can you please explain what the reason you want that extension string to be added?
Thank you.