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Meter Provider

It’s a common use-case to attach tags dynamically to a Meter. Let’s say we execute a job and we want to use a Timer to instrument it:

Timer.Sample sample = Timer.start(registry);

Result result = job.execute();

Timer timer = Timer.builder("job.execution")
    .tag("job.name", "job")
    .tag("status", result.status())
    .register(registry);
sample.stop(timer);

This lets us dynamically determine the status tag from the end state of the operation we are timing. There are two drawbacks of doing this:

Every time the above is executed, a new Timer.Builder instance is created. This increases the amount of data that the GC needs to collect.
The code above is somewhat boilerplate, it does not let you define the common properties of a Timer and attach what is dynamically changing but everything is always present.

In some cases you can use registry.timer("job.execution", "job.name", "my-job", "status", result.status()) instead of using Timer.Builder which can save you some extra objects but this is not always possible.

You can resolve both of these issues by using a MeterProvider. It’s a convenience interface to create new meters from tags using a common "template".

Not every Meter can do this, MeterProvider can be used with Counter, Timer, LongTaskTimer, and DistributionSummary.

Here’s what you can do instead of the above:

private MeterProvider<Timer> timerProvider = Timer.builder("job.execution")
    .tag("job.name", "my-job")
    .withRegistry(registry); (1)

// ...

Timer.Sample sample = Timer.start(registry);

Result result = job.execute();

sample.stop(timerProvider.withTags("status", result.status())); (2)

1	Definition of the `MeterProvider` for `Timer` with all the "static" fields necessary. Please note the `withRegistry` method call.
2	Definition of the dynamic tags. Note that only those tags are defined here that are dynamic and everying else is defined where the `MeterProvider` is created. The `withTags` method returns a `Timer` that is created using the tags defined in `withTags` plus everything else that is defined by the `MeterProvider`.

This and the previous example produce the same output, the only difference is the amount of boilerplate in your code and the amount of builder objects created in the heap.