content: /*
   * Copyright (c) 2007, 2020, Oracle and/or its affiliates.
   *
   * This program is free software; you can redistribute it and/or modify it under
   * the terms of the GNU General Public License, version 2.0, as published by the
   * Free Software Foundation.
   *
   * This program is also distributed with certain software (including but not
   * limited to OpenSSL) that is licensed under separate terms, as designated in a
   * particular file or component or in included license documentation. The
   * authors of MySQL hereby grant you an additional permission to link the
   * program and your derivative works with the separately licensed software that
   * they have included with MySQL.
   *
   * Without limiting anything contained in the foregoing, this file, which is
   * part of MySQL Connector/J, is also subject to the Universal FOSS Exception,
   * version 1.0, a copy of which can be found at
   * http://oss.oracle.com/licenses/universal-foss-exception.
   *
   * 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, version 2.0,
   * 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.cj.jdbc.ha;
  
  import java.lang.reflect.InvocationHandler;
  import java.sql.SQLException;
  import java.util.List;
  import java.util.Map;
  
  import com.mysql.cj.jdbc.ConnectionImpl;
  import com.mysql.cj.jdbc.JdbcConnection;
  
  /**
   * 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 blocklist-aware.
   */
  public class SequentialBalanceStrategy implements BalanceStrategy {
      private int currentHostIndex = -1;
  
      public SequentialBalanceStrategy() {
      }
  
      @Override
      public ConnectionImpl pickConnection(InvocationHandler proxy, List<String> configuredHosts, Map<String, JdbcConnection> liveConnections,
              long[] responseTimes, int numRetries) throws SQLException {
          int numHosts = configuredHosts.size();
  
          SQLException ex = null;
  
          Map<String, Long> blockList = ((LoadBalancedConnectionProxy) proxy).getGlobalBlocklist();
  
          for (int attempts = 0; attempts < numRetries; attempts++) {
              if (numHosts == 1) {
                  this.currentHostIndex = 0; // pathological case
              } else if (this.currentHostIndex == -1) {
                  int random = (int) Math.floor((Math.random() * numHosts));
  
                  for (int i = random; i < numHosts; i++) {
                      if (!blockList.containsKey(configuredHosts.get(i))) {
                          this.currentHostIndex = i;
                          break;
                      }
                  }
  
                  if (this.currentHostIndex == -1) {
                      for (int i = 0; i < random; i++) {
                          if (!blockList.containsKey(configuredHosts.get(i))) {
                              this.currentHostIndex = i;
                              break;
                          }
                      }
                  }
  
                  if (this.currentHostIndex == -1) {
                      blockList = ((LoadBalancedConnectionProxy) proxy).getGlobalBlocklist(); // it may have changed
                      // and the proxy returns a copy
  
                      try {
                          Thread.sleep(250);
                      } catch (InterruptedException e) {
                      }
  
                      continue; // retry
                  }
              } else {
  
                  int i = this.currentHostIndex + 1;
                  boolean foundGoodHost = false;
  
                  for (; i < numHosts; i++) {
                      if (!blockList.containsKey(configuredHosts.get(i))) {
                          this.currentHostIndex = i;
                          foundGoodHost = true;
                          break;
                      }
                  }
  
                  if (!foundGoodHost) {
                      for (i = 0; i < this.currentHostIndex; i++) {
                          if (!blockList.containsKey(configuredHosts.get(i))) {
                              this.currentHostIndex = i;
                              foundGoodHost = true;
                              break;
                          }
                      }
                  }
  
                  if (!foundGoodHost) {
                      blockList = ((LoadBalancedConnectionProxy) proxy).getGlobalBlocklist(); // it may have changed
                      // and the proxy returns a copy
  
                      try {
                          Thread.sleep(250);
                      } catch (InterruptedException e) {
                      }
  
                      continue; // retry
                  }
              }
  
              String hostPortSpec = configuredHosts.get(this.currentHostIndex);
  
              ConnectionImpl conn = (ConnectionImpl) liveConnections.get(hostPortSpec);
  
              if (conn == null) {
                  try {
                      conn = ((LoadBalancedConnectionProxy) proxy).createConnectionForHost(hostPortSpec);
                  } catch (SQLException sqlEx) {
                      ex = sqlEx;
  
                      if (((LoadBalancedConnectionProxy) proxy).shouldExceptionTriggerConnectionSwitch(sqlEx)) {
  
                          ((LoadBalancedConnectionProxy) proxy).addToGlobalBlocklist(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
      }
  
  }
  