hbase-noop-htrace/src/main/java/org/apache/htrace/core/Sampler.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.htrace.core;

/**
 * Extremely simple callback to determine the frequency that an action should
 * be performed.
 *
 * <p>For example, the next() function may look like this:</p>
 * <pre>
 * <code>
 * public boolean next() {
 *   return Math.random() &gt; 0.5;
 * }
 * </code>
 * </pre>
 * <p>This would trace 50% of all gets, 75% of all puts and would not trace any
 * other requests.</p>
 */
public abstract class Sampler {
  /**
   * A {@link Sampler} builder. It takes a {@link Sampler} class name and
   * constructs an instance of that class, with the provided configuration.
   */
  public static class Builder {
    public Builder(HTraceConfiguration conf) {
    }

    public Builder reset() {
      return this;
    }

    public Builder className(String className) {
      return this;
    }

    public Builder classLoader(ClassLoader classLoader) {
      return this;
    }

    public Sampler build() {
      return NEVER;
    }
  }

  public static final Sampler ALWAYS = AlwaysSampler.INSTANCE;
  public static final Sampler NEVER = NeverSampler.INSTANCE;

  public abstract boolean next();
}