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Simple persistent scheduler for scheduled tasks, recurring or ad-hoc.

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/*
 * Copyright (C) Gustav Karlsson
 *
 * Licensed 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 com.github.kagkarlsson.scheduler;

public class PollingStrategyConfig {

  public static final PollingStrategyConfig DEFAULT_FETCH =
      new PollingStrategyConfig(Type.FETCH, 0.5, 3.0);

  public static final PollingStrategyConfig DEFAULT_SELECT_FOR_UPDATE =
      new PollingStrategyConfig(Type.LOCK_AND_FETCH, 0.5, 1.0);

  public int getUpperLimit(int threadpoolSize) {
    return (int) (upperLimitFractionOfThreads * threadpoolSize);
  }

  public int getLowerLimit(int threadpoolSize) {
    return (int) (lowerLimitFractionOfThreads * threadpoolSize);
  }

  public enum Type {
    LOCK_AND_FETCH,
    FETCH,
  }

  public final Type type;
  public final double lowerLimitFractionOfThreads;
  public final double upperLimitFractionOfThreads;

  public PollingStrategyConfig(
      Type type, double lowerLimitFractionOfThreads, double upperLimitFractionOfThreads) {
    this.type = type;
    this.lowerLimitFractionOfThreads = lowerLimitFractionOfThreads;
    this.upperLimitFractionOfThreads = upperLimitFractionOfThreads;
    if (lowerLimitFractionOfThreads >= upperLimitFractionOfThreads) {
      throw new IllegalArgumentException(
          "lowerLimitFractionOfThreads should be lower than upperLimitFractionOfThreads");
    }

    if (upperLimitFractionOfThreads < 1.0) {
      throw new IllegalArgumentException(
          "upperLimit should be equals to number of threads or higher, i.e. fraction higher than 1");
    }
  }

  public String describe() {
    return "type="
        + type.name()
        + ", lowerLimit="
        + lowerLimitFractionOfThreads
        + ", upperLimit="
        + upperLimitFractionOfThreads;
  }
}