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// Copyright 2016 Yahoo Inc. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.jdisc;
import com.google.inject.ProvidedBy;
import com.google.inject.Provider;
import com.yahoo.jdisc.application.MetricConsumer;
import com.yahoo.jdisc.application.MetricProvider;
import java.util.Map;
/**
* <p>This interface provides an API for writing metric data to the configured {@link MetricConsumer}. If no {@link
* Provider} for the MetricConsumer class has been bound by the application, all calls to this interface are no-ops. The
* implementation of this interface uses thread local consumer instances, so as long as the {@link MetricConsumer} is
* thread-safe, so is this.</p>
*
* <p>An instance of this class can be injected anywhere.</p>
*
* @author Simon Thoresen
*/
@ProvidedBy(MetricProvider.class)
public interface Metric {
/**
* <p>Set a metric value. This is typically used with histogram-type metrics.</p>
*
* @param key The name of the metric to modify.
* @param val The value to assign to the named metric.
* @param ctx The context to further describe this entry.
*/
void set(String key, Number val, Context ctx);
/**
* <p>Add to a metric value. This is typically used with counter-type metrics.</p>
*
* @param key The name of the metric to modify.
* @param val The value to add to the named metric.
* @param ctx The context to further describe this entry.
*/
void add(String key, Number val, Context ctx);
/**
* <p>Creates a {@link MetricConsumer}-specific {@link Context} object that encapsulates the given properties. The
* returned Context object should be passed along every future call to {@link #set(String, Number, Context)} and
* {@link #add(String, Number, Context)} where the properties match those given here.</p>
*
* @param properties The properties to incorporate in the context.
* @return The created context.
*/
Context createContext(Map<String, ?> properties);
/**
* <p>Declares the interface for the arbitrary context object to pass to both the {@link
* #set(String, Number, Context)} and {@link #add(String, Number, Context)} methods. This is intentionally empty so
* that implementations can vary.</p>
*/
interface Context {
}
}
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