/*
 * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package org.openjdk.btrace.core.annotations;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * Marks an {@linkplain OnMethod} handler as a sampled one. When a handler is sampled not all events
 * will be traced - only a statistical sample with the given mean.
 *
 * <p>By default an adaptive sampling is used. BTrace will increase or decrease the number of
 * invocations between samples to keep the mean time window, thus decreasing the overall overhead.
 *
 * @author Jaroslav Bachorik
 */
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.CLASS)
public @interface Sampled {
  int MEAN_DEFAULT = 10;

  /**
   * The sampler kind
   *
   * @return The sampler kind
   */
  Sampler kind() default Sampler.Const;

  /**
   * The sampler mean.
   *
   * <p>For {@code Sampler.Const} it is the average number of events between samples.<br>
   * For {@code Sampler.Adaptive} it is the average time (in ns) between samples<br>
   *
   * @return The sampler mean
   */
  int mean() default MEAN_DEFAULT;

  /**
   * Specifies the sampler kind
   *
   * <ul>
   *   <li>{@code None} - no sampling
   *   <li>{@code Const} - keeps the average number of events between samples
   *   <li>{@code Adaptive} - increases or decreases the average number of events between samples to
   *       lower overhead
   * </ul>
   */
  enum Sampler {
    /** No Sampling */
    None,
    /** Keeps the average number of events between samples */
    Const,
    /** Increases or decreases the average number of events between samples to lower overhead */
    Adaptive
  }
}
