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SequentialBalanceStrategy.java

/*
 Copyright (c) 2007, 2010, 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.List;
import java.util.Map;
import java.util.Properties;

/**
 * A balancing strategy that starts at a random point, and then advances
 * in the list (wrapping around) for each new pickConnection() call.
 * 
 * The initial point selection, and subsequent point selections are
 * blacklist-aware.
 *
 */
00039 public class SequentialBalanceStrategy implements BalanceStrategy {
      private int currentHostIndex = -1;
      
      public SequentialBalanceStrategy() {
      }

00045       public void destroy() {
            // we don't have anything to clean up
      }

00049       public void init(Connection conn, Properties props) throws SQLException {
            // we don't have anything to initialize
      }

00053       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;

            Map<String, Long> blackList = proxy.getGlobalBlacklist();

            for (int attempts = 0; attempts < numRetries;) {
                  if (numHosts == 1) {
                        currentHostIndex = 0; // pathological case
                  } else  if (currentHostIndex == -1) {
                        int random = (int) Math.floor((Math.random() * numHosts));
                        
                        for (int i = random; i < numHosts; i++) {
                              if (!blackList.containsKey(configuredHosts.get(i))) {
                                    currentHostIndex = i; 
                                    break;
                              }
                        }
                        
                        if (currentHostIndex == -1) {
                              for (int i = 0; i < random; i++) {
                                    if (!blackList.containsKey(configuredHosts.get(i))) {
                                          currentHostIndex = i; 
                                          break;
                                    }
                              }
                        }
                        
                        if (currentHostIndex == -1) {
                              blackList = proxy.getGlobalBlacklist(); // it may have changed
                                                // and the proxy returns a copy
                              
                              try {
                                    Thread.sleep(250);
                              } catch (InterruptedException e) {
                              }

                              continue; // retry
                        }
                  } else {

                        
                        int i = currentHostIndex + 1;
                        boolean foundGoodHost = false;
                        
                        for (; i < numHosts; i++) {
                              if (!blackList.containsKey(configuredHosts.get(i))) {
                                    currentHostIndex = i;
                                    foundGoodHost = true;
                                    break;
                              }
                        }

                        if (!foundGoodHost) {
                              for (i = 0; i < currentHostIndex; i++) {
                                    if (!blackList.containsKey(configuredHosts.get(i))) {
                                          currentHostIndex = i;
                                          foundGoodHost = true;
                                          break;
                                    }
                              }
                        }
                  
                        if (!foundGoodHost) {
                              blackList = proxy.getGlobalBlacklist(); // it may have changed
                              // and the proxy returns a copy
            
                              try {
                                    Thread.sleep(250);
                              } catch (InterruptedException e) {
                              }
                  
                              continue; // retry
                        }
                  }

                  String hostPortSpec = configuredHosts.get(currentHostIndex);

                  ConnectionImpl conn = liveConnections.get(hostPortSpec);

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

                              if (sqlEx instanceof CommunicationsException
                                          || "08S01".equals(sqlEx.getSQLState())) {

                                    proxy.addToGlobalBlacklist( hostPortSpec );

                                    try {
                                          Thread.sleep(250);
                                    } catch (InterruptedException e) {
                                    }
                                    
                                    continue;
                              } else {
                                    throw sqlEx;
                              }
                        }
                  }
                  
                  return conn;
            }

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

            return null; // we won't get here, compiler can't tell
      }

}

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