src/org/objectweb/cjdbc/controller/loadbalancer/policies/errorchecking/ErrorCheckingRoundRobin.java

説明を見る。

package org.objectweb.cjdbc.controller.loadbalancer.policies.errorchecking;

import java.util.ArrayList;

import org.objectweb.cjdbc.controller.backend.DatabaseBackend;

public class ErrorCheckingRoundRobin extends ErrorCheckingPolicy
{
  private int index = 0;

  public ErrorCheckingRoundRobin(int numberOfNodes)
  {
    super(ErrorCheckingPolicy.ROUND_ROBIN, numberOfNodes);
  }

  public ArrayList getBackends(ArrayList backends)
    throws ErrorCheckingException
  {
    int size = backends.size();

    if (nbOfNodes == 0)
      return null;
    else if (nbOfNodes == size)
      return backends;

    ArrayList result = new ArrayList(nbOfNodes);
    ArrayList clonedList = new ArrayList(size);
    for (int i = 0; i < size; i++)
    { // Take all enabled backends
      DatabaseBackend db = (DatabaseBackend) backends.get(i);
      if (db.isReadEnabled() || db.isWriteEnabled())
        clonedList.add(db);
    }

    int clonedSize = clonedList.size();

    if (nbOfNodes == clonedSize)
      return backends;
    else if (nbOfNodes > clonedSize)
      throw new ErrorCheckingException(
        "Asking for more backends ("
          + nbOfNodes
          + ") than available ("
          + clonedSize
          + ")");

    synchronized (this)
    { // index must be modified in mutual exclusion
      for (int i = 0; i < nbOfNodes; i++)
      {
        index = (index + 1) % clonedSize;
        result.add(clonedList.remove(index));
      }
    }

    return result;
  }

  public String getInformation()
  {
    return "Error checking using "
      + nbOfNodes
      + " nodes choosen using a round-robin algorithm";
  }
}

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