Converts a code block to a com.codahale.metrics.health.HealthCheck and registers it.

Use it as follows:

object Application {
  // The application wide health check registry.
  val healthCheckRegistry = new com.codahale.metrics.health.HealthCheckRegistry()
}
trait Checked extends CheckedBuilder {
  val registry = Application.healthCheckRegistry
}

class ExampleWorker extends Checked {
  healthCheck("alive") { workerThreadIsActive() }
}

The code block must have a result of type Boolean, Try, Either, Future, com.codahale.metrics.health.HealthCheck.Result, or simply Unit.

• A check result of true indicates healthy, false indicates unhealthy.
• A check result of type Success indicates healthy, Failure indicates unhealthy. The embedded value (after applying .toString) or throwable is used as (un)healthy message.
• A check result of type Future will have 3 seconds to execute (by default). The result of the execution will be treated as Success or Failure.
• A check result of type Right indicates healthy, Left[Any] or Left[Throwable] indicates unhealthy. The embedded value (after applying .toString) or throwable is used as (un)healthy message.
• If the check result is of type com.codahale.metrics.health.HealthCheck.Result, the result is passed unchanged.
• A check result of type Unit indicates healthy.
• If a checker throws an exception, the result is considered unhealthy with the throwable as unhealthy message.

It is also possible to override the health check base name. For example:

class ExampleWorker extends Checked {
  override lazy val metricBaseName = MetricName("Overridden.Base.Name")
  healthCheck("alive") { workerThreadIsActive() }
}

To change the timeout for Future execution, set an implicit duration:

class ExampleWorker extends Checked {
  implicit private val timeout = 10.seconds
  healthCheck("alive")(Future { workerThreadIsActive() })
}

NOTE: only one health check can be registered under a name (including the base name which is derived from the
class name by default). Any subsequent health check registrations will be ignored. This happens for example
when a class that defines a health check is instantiated multiple times. This metrics-core behavior might be
changed with https://github.com/dropwizard/metrics/issues/1245.

@param name the name of the health check
@param unhealthyMessage the unhealthy message for checkers that return `false`, defaults to `"Health check failed"`
@param checker the code block that does the health check

The base name for all metrics created from this builder.