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• Custom Metrics are based on the New Metric System.
• Provide essential ready-to-use metrics like LongMetric which can be exported by a existing metric exporter.
• User can store own metrics in different registers corresponding to metrics groups.
• Custom metrics are separated from the internals by registry name by name prefix "custom.".
• Custom metrics management might require a permission.
• We should document examples of effecient metrics implementations like LongAdder.

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/**
 * Manages custom metrics. Metrics have full name and are grouped into registries. Registry name is part of the full metric name until last '.'. 
 * Metric name is the last part of the full name. Names of custom metrics registers are always storedprefixed with the prefix "custom.".
 * For example, Ifif provided registryfull name is "a.b.c.regnamemname", it is automatically converted to "custom.a.b.c.regnamemname".
 * If thefull name is "custom.a.b.c.regnamemname", it is used as is. Where "custom.a.b.c" is the registry name and "mname" is the metric name. 
 */
public interface IgniteCustomMetrics {
    /**
     * Registers metric in registry {@code registryName}. Adds new metric registry if absent. 
     *
     * @return Previous metric if it already exists. with the same name. Otherwise, {@code metric} otherwise. 
     */
    <T extends Metric> T metric(String registryName, String metricNamefullName, T metric);

    /** Removes metric from registry {@code registryName}. */
    void removeMetric(String registryName, String metricNamefullName);

    /** @return Certain Metricmetric registry named '{@code registryName}'. */
    ReadOnlyMetricRegistry registry(String registryName);

    /** Removes registry named '{@code registryName}'  and all its metrics. */
    void removeRegistry(String registryName);


    // Essential metrics. Int, Long and Double should be enough.

    /**
     * Registers a {@link LongMetric} in registry {@code registryName}. Adds new metric registry if absent.
     *
     * @return Previous long value setter if it already exists with the same name. A new one otherwise.
     */
    LongConsumer longMetric(String registryName, String metricNamefullName, @Nullable String description);

    /**
     * Registers a {@link DoubleMetric} in registry {@code registryName}. Adds new metric registry if absent.
     *
     * @return Previous double value setter if it already exists with the same name. A new one otherwise.
     */
    DoubleConsumer doubleMetric(String registryNamefullName, String metricName, @Nullable String description);

    /**
     * Registers a {@link IntMetric} in registry {@code registryName}. Adds new metric registry if absent.
     *
     * @return Previous int value setter if it already exists with the same name. A new one otherwise.
     */
    IntConsumer booleanMetric(String registryName, String metricNamefullName, @Nullable String description);



    // Might be useful the gauges.

    /**
     * Registers a {@link LongMetric} metric in registry {@code registryName} with long value supplier {@code valueSupplier}. 
     * Adds new metric registry if absent.
     *
     * @return {@code True} if metric was added. {@code False} if another meric already exists under the same name.  
     */
    boolean longMetric(String registryName, String metricNamefullName, LongSupplier valueSupplier, @Nullable String description);

    /**
     * Registers a {@link DoubleMetric} metric in registry {@code registryName} with double value supplier {@code valueSupplier}. 
     * Adds new metric registry if absent.
     *
     * @return {@code True} if metric was added. {@code False} if another meric already exists under the same name.  
     */
    boolean doubleMetric(String registryName, String metricNamefullName, DoubleSupplier valueSupplier, @Nullable String description);

    /**
     * Registers a {@link IntMetric} metric in registry {@code registryName} with int value supplier {@code valueSupplier}. 
     * Adds new metric registry if absent.
     * 
     * @return {@code True} if metric was added. {@code False} if another meric already exists under the same name.  
     */
    boolean intMetric(String registryName, String metricNamefullName, BooleanSupplier valueSupplier, @Nullable String description);
}

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