source: Ballon/out/artifacts/geisa_artifact/WEB-INF/lib/mysql-connector-java-5.1.21/src/com/mysql/jdbc/SequentialBalanceStrategy.java

/*
 Copyright (c) 2007, 2012, 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.
 *
 */
public class SequentialBalanceStrategy implements BalanceStrategy {
        private int currentHostIndex = -1;
        
        public SequentialBalanceStrategy() {
        }

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

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

        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;
                                        }
                                        throw sqlEx;
                                }
                        }
                        
                        return conn;
                }

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

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

}