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RandomBalanceStrategy.java

/*
 Copyright (c) 2007, 2011, Oracle and/or its affiliates. All rights reserved.
 

  The MySQL Connector/J is licensed under the terms of the GPLv2
  <http://www.gnu.org/licenses/old-licenses/gpl-2.0.html>, like most MySQL Connectors.
  There are special exceptions to the terms and conditions of the GPLv2 as it is applied to
  this software, see the FLOSS License Exception
  <http://www.mysql.com/about/legal/licensing/foss-exception.html>.

  This program is free software; you can redistribute it and/or modify it under the terms
  of the GNU General Public License as published by the Free Software Foundation; version 2
  of the License.

  This program 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 for more details.

  You should have received a copy of the GNU General Public License along with this
  program; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth
  Floor, Boston, MA 02110-1301  USA
 
 */
package com.mysql.jdbc;

import java.sql.SQLException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Properties;

00033 public class RandomBalanceStrategy implements BalanceStrategy {

      public RandomBalanceStrategy() {
      }

00038       public void destroy() {
            // we don't have anything to clean up
      }

00042       public void init(Connection conn, Properties props) throws SQLException {
            // we don't have anything to initialize
      }

00046       public ConnectionImpl pickConnection(LoadBalancingConnectionProxy proxy,
                  List<String> configuredHosts, Map<String, ConnectionImpl> liveConnections, long[] responseTimes,
                  int numRetries) throws SQLException {
            int numHosts = configuredHosts.size();

            SQLException ex = null;

            List<String> whiteList = new ArrayList<String>(numHosts);
            whiteList.addAll(configuredHosts);
            
            Map<String, Long> blackList = proxy.getGlobalBlacklist();

            whiteList.removeAll(blackList.keySet());
            
            Map<String, Integer> whiteListMap = this.getArrayIndexMap(whiteList);
            

            for (int attempts = 0; attempts < numRetries;) {
                  int random = (int) Math.floor((Math.random() * whiteList.size()));
                  if(whiteList.size() == 0){
                        throw SQLError.createSQLException("No hosts configured", null);
                  }

                  String hostPortSpec = whiteList.get(random);

                  ConnectionImpl conn = liveConnections.get(hostPortSpec);

                  if (conn == null) {
                        try {
                              conn = proxy.createConnectionForHost(hostPortSpec);
                        } catch (SQLException sqlEx) {
                              ex = sqlEx;

                              if (proxy.shouldExceptionTriggerFailover(sqlEx)) {

                                    Integer whiteListIndex = whiteListMap.get(hostPortSpec);

                                    // exclude this host from being picked again
                                    if (whiteListIndex != null) {
                                          whiteList.remove(whiteListIndex.intValue());
                                          whiteListMap = this.getArrayIndexMap(whiteList);
                                    }
                                    proxy.addToGlobalBlacklist( hostPortSpec );

                                    if (whiteList.size() == 0) {
                                          attempts++;
                                          try {
                                                Thread.sleep(250);
                                          } catch (InterruptedException e) {
                                          }

                                          // start fresh
                                          whiteListMap = new HashMap<String, Integer>(numHosts);
                                          whiteList.addAll(configuredHosts);
                                          blackList = proxy.getGlobalBlacklist();

                                          whiteList.removeAll(blackList.keySet());
                                          whiteListMap = this.getArrayIndexMap(whiteList);
                                    }

                                    continue;
                              } else {
                                    throw sqlEx;
                              }
                        }
                  }
                  
                  return conn;
            }

            if (ex != null) {
                  throw ex;
            }

            return null; // we won't get here, compiler can't tell
      }
      
      private Map<String, Integer> getArrayIndexMap(List<String> l) {
            Map<String, Integer> m = new HashMap<String, Integer>(l.size());
            for (int i = 0; i < l.size(); i++) {
                  m.put(l.get(i), Integer.valueOf(i));
            }
            return m;
            
      }

}

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