Metacat

/**

 *  '$RCSfile$'

 *    Purpose: A class represent a DBConnection pool. Another user can use the

 *    object to initial a connection pool, get db connection or return it. 

 *  Copyright: 2000 Regents of the University of California and the

 *             National Center for Ecological Analysis and Synthesis

 *    Authors: Jing Tao

 *    Release: @release@

 *

 *   '$Author: tao $'

 *     '$Date: 2002-06-14 09:36:04 -0700 (Fri, 14 Jun 2002) $'

 * '$Revision: 1220 $'

 *

 * 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; either version 2 of the License, or

 * (at your option) any later version.

 *

 * 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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

 */

package edu.ucsb.nceas.metacat;

import java.io.*;

import java.util.Vector;

import java.lang.*;

import java.sql.*;

import java.util.Stack;

import java.util.Hashtable;

import java.util.Enumeration;

/** 

 * A class represent a DBConnection pool. Another user can use the

 * object to initial a connection pool, get db connection or return it.

 * This a singleton class, this means only one instance of this class could

 * be in the program at one time. 

 */

public class DBConnectionPool implements Runnable

{

  //static attributes

  private static DBConnectionPool instance;

  private static Vector connectionPool;

  private static Thread runner;

  //maximum connection number in the connection pool

  final static int MAXIMUMCONNECTIONNUMBER=

                  Integer.parseInt(MetaCatUtil.getOption("maximumConnections"));

  //inintila connection number int the connection pool

  final static int INITIALCONNECTIONNUMBER=

                  Integer.parseInt(MetaCatUtil.getOption("initialConnections"));

  //the number to increase connection pool size

  final static int INCREASECONNECTIONNUMBER=

                Integer.parseInt(MetaCatUtil.getOption("incrementConnections"));

  //maximum age for a connection (in milli seconds)

  final static long MAXIMUMAGE =

                  Long.parseLong(MetaCatUtil.getOption("maximumConnectionAge"));

  //maximum connection time for a connection ( in milli second)

  final static long MAXIMUMCONNECTIONTIME =

                 Long.parseLong(MetaCatUtil.getOption("maximumConnectionTime"));

  //maximum number for using a connection.

  final static int MAXIMUMUSAGENUMBER =

                  Integer.parseInt(MetaCatUtil.getOption("maximumUsageNumber"));

  //the parameter if run dbconncestionrecyclethread or not

  final static String DBCONNECTIONRECYCLETHREAD =

                          MetaCatUtil.getOption("runDBConnectionRecycleThread");

  //the cycle time of connection recycle action

  final static long CYCLETIMEOFDBCONNECTION = 

               Long.parseLong(MetaCatUtil.getOption("cycleTimeOfDBConnection"));

  //the number for trying to check out a connection in the pool in 

  //getDBConnection method

  final static int LIMIT = 2;

  final static int FREE = 0; //status of a connection

  final static int BUSY = 1; //statis of a connection

  /**

   * Returns the single instance, creating one if it's the

   * first time this method is called.

   */

  public static synchronized DBConnectionPool getInstance()

                                 throws SQLException 

  {

    MetaCatUtil.debugMessage

                      ("MaximumConnectionNumber: "+MAXIMUMCONNECTIONNUMBER, 49);

    MetaCatUtil.debugMessage

                     ("Intial connection number: "+INITIALCONNECTIONNUMBER, 49);

    MetaCatUtil.debugMessage

                 ("Increated connection Number: "+INCREASECONNECTIONNUMBER, 49);

    MetaCatUtil.debugMessage

                  ("Maximum connection age: "+MAXIMUMAGE, 49);

    MetaCatUtil.debugMessage

                  ("Maximum connection time: "+MAXIMUMCONNECTIONTIME, 49);

    MetaCatUtil.debugMessage

                  ("Maximum usage count: "+MAXIMUMUSAGENUMBER, 49);

    MetaCatUtil.debugMessage

             ("Running recycle thread or not: "+DBCONNECTIONRECYCLETHREAD, 49);

    MetaCatUtil.debugMessage

             ("Cycle time of recycle: "+CYCLETIMEOFDBCONNECTION, 49); 

    if (instance == null) 

    {

      instance = new DBConnectionPool();

    }

    return instance;

  }//getInstance

  /**

   * This is a private constructor since it is singleton

   */

  private DBConnectionPool()  throws SQLException 

  {

    connectionPool = new Vector();

    initialDBConnectionPool();

    //running the thread to recycle DBConnection

    if (DBCONNECTIONRECYCLETHREAD.equals("on"))

    {

      runner = new Thread(this);

      runner.start();

    }

  }//DBConnection

  /**

   * Method to get the size of DBConnectionPool

   */

  public int getSizeOfDBConnectionPool()

  {

    return connectionPool.size();

  }

  /**

   * Method to initial a pool of DBConnection objects 

   */

  private void initialDBConnectionPool() throws SQLException 

  {

    DBConnection dbConn = null;

    for ( int i = 0; i < INITIALCONNECTIONNUMBER; i++ ) 

    {

      //create a new object of DBConnection

      //this DBConnection object has a new connection in it

      //it automatically generate the createtime and tag

      dbConn = new DBConnection();

      //put DBConnection into vetor

      connectionPool.add(dbConn);

    }    

  }//initialDBConnectionPool

  /**

   * Method to get Connection object (Not DBConnection)

   */

  /*public static Connection getConnection() throws SQLException

  {

    DBConnection dbConn = null;

    //get a DBConnection

    dbConn = getDBConnection();

    //get connection object in DBConnection object

    //The following getConnections method is in DBConnection class

    return dbConn.getConnections();

  }*/

  /**

   * Method to get a DBConnection in connection pool

   * 1) try to get a DBConnection from DBConnection pool

   * 2) if 1) failed, then check the size of pool. If the size reach the

   *    maximum number of connection, throw a exception: couldn't get one

   * 3) If the size is less than the maximum number of connectio, create some

   *    new connections and recursive get one

   * @param methodName, the name of method which will check connection out

   */

  public static synchronized DBConnection getDBConnection(String methodName) 

                                                throws SQLException

  {

    DBConnection db = null;

    int random = 0; //random number

    int index = 0; //index

    int size = 0; //size of connection pool

    MetaCatUtil.debugMessage("Try to checking out connection...", 45);

    size = connectionPool.size();

    MetaCatUtil.debugMessage("size of connection pool: "+size, 45);

     //try every DBConnection in the pool

    //every DBConnection will be try LIMITE times

    for (int j=0 ; j<LIMIT; j++)

    {

       //create a random number as the started index for connection pool

      //So that the connection ofindex of 0 wouldn't be a the heaviest user

      random = (new Double (Math.random()*100)).intValue();

      for (int i=0; i<size; i++)

      {

        index =(i+random)%size;

        db = (DBConnection) connectionPool.elementAt(index);

        MetaCatUtil.debugMessage("Index: "+index, 45);

        MetaCatUtil.debugMessage("Tag: "+db.getTag(), 45);

        MetaCatUtil.debugMessage("Status: "+db.getStatus(), 45);

        //check if the connection is free

        if (db.getStatus()==FREE)

        {

          //If this connection is good, return this DBConnection

          if (validateDBConnection(db))

          {

            //set this DBConnection status

            db.setStatus(BUSY);

            //increase checkout serial number

            db.increaseCheckOutSerialNumber(1);

            //increase one usageCount

            db.increaseUsageCount(1);

            //set method name to DBConnection

            db.setCheckOutMethodName(methodName);

            //debug message

            MetaCatUtil.debugMessage("The connection is checked out: "

                                       +db.getTag(), 35);

            MetaCatUtil.debugMessage("The method for checking is: " 

                                              +db.getCheckOutMethodName(), 35);

            MetaCatUtil.debugMessage("The age is "+db.getAge(), 40);

            MetaCatUtil.debugMessage("The usage is "+db.getUsageCount(), 40);

            MetaCatUtil.debugMessage("The conection time it has: "

                                                +db.getConnectionTime(), 40);

            //set check out time

            db.setCheckOutTime(System.currentTimeMillis());

            //check it out

            return db;

          }//if

          else//The DBConnection has some problem

          {

            //close this DBConnection

            db.close();

            //remove it form connection pool

            connectionPool.remove(index);

            //insert a new DBConnection to same palace

            db = new DBConnection();

            connectionPool.insertElementAt(db, index);

          }//else

        }//if

      }//for

    }//for

    //if couldn't get a connection, we should increase DBConnection pool

    //if the connection pool size is less than maximum connection number

    if ( size < MAXIMUMCONNECTIONNUMBER )

    {

       if ((size+INCREASECONNECTIONNUMBER) < MAXIMUMCONNECTIONNUMBER)

       { 

         //if we can create INCREASECONNECTIONNUMBER of new DBConnection

         //add to connection pool

         for ( int i=0; i<INCREASECONNECTIONNUMBER; i++)

         {

           DBConnection dbConn = new DBConnection();

           connectionPool.add(dbConn);

         }//for

       }//if

       else

       {

         //There is no enough room to increase INCREASECONNECTIONNUMBER 

         //we create new DBCoonection to Maximum connection number

         for (int i= size+1; i<= MAXIMUMCONNECTIONNUMBER; i++)

         {

           DBConnection dbConn = new DBConnection();

           connectionPool.add(dbConn);

         }//for

       }//else

    }//if

    else

    {

      /*throw new SQLException("The maximum of " +MAXIMUMCONNECTIONNUMBER + 

                            " open db connections is reached." +

                            " New db connection to MetaCat" +

                            " cannot be established.");*/

       MetaCatUtil.debugMessage("The maximum of " +MAXIMUMCONNECTIONNUMBER + 

                            " open db connections is reached." +

                            " New db connection to MetaCat" +

                            " cannot be established.", 1);

       return null;

       //if couldn't get a connection, sleep 20 seconds and try again.

       /*try

       {

         System.out.println("sleep");

         Thread.sleep(2000);

       }

       catch (Exception e)

       {

       }*/

    }//else

    //recursive to get new connection    

    return getDBConnection(methodName); 

  }//getDBConnection

  /** 

   * Method to check if a db connection works fine or not

   * Check points include:

   * 1. check the usageCount if it is too many

   * 2. check the dbconne age if it is too old

   * 3. check the connection time if it is too long

   * 4. run simple sql query

   *

   * @param dbConn, the DBConnection object need to check

   */

  private static boolean validateDBConnection (DBConnection dbConn)

  {

    //Check if the DBConnection usageCount if it is too many

    if (dbConn.getUsageCount() >= MAXIMUMUSAGENUMBER )

    {

      MetaCatUtil.debugMessage("Connection usageCount is too many: "+

      dbConn.getUsageCount(), 40);

      return false;

    }

    //Check if the DBConnection has too much connection time

    if (dbConn.getConnectionTime() >= MAXIMUMCONNECTIONTIME)

    {

      MetaCatUtil.debugMessage("Connection has too much connection time: "+

      dbConn.getConnectionTime(), 40);

      return false;

    }

    //Check if the DBConnection is too old

    if (dbConn.getAge() >=MAXIMUMAGE)

    {

      MetaCatUtil.debugMessage("Connection is too old: "+dbConn.getAge(), 40);

      return false;

    }

    //Try to run a simple query

    try

    {

      long startTime=System.currentTimeMillis();

      DatabaseMetaData metaData = dbConn.getMetaData();

      long stopTime=System.currentTimeMillis();

      //increase one usagecount

      dbConn.increaseUsageCount(1);

      //increase connection time

      dbConn.setConnectionTime(stopTime-startTime);

    }

    catch (Exception e)

    {

      MetaCatUtil.debugMessage("Error in validateDBConnection: "

                                +e.getMessage(), 30);

      return false;

    }

    return true;

  }//validateDBConnection()

  /**

   * Method to return a connection to DBConnection pool.

   * @param conn, the Connection object need to check in

   */

  public static synchronized void returnDBConnection(DBConnection conn, 

                                                              int serialNumber)

  {

    int index = -1;

    DBConnection dbConn = null;

    index = getIndexOfPoolForConnection(conn);

    if ( index ==-1 )

    {

      MetaCatUtil.debugMessage("Couldn't find a DBConnection in the pool"

                                  +" which have same tag to the returned"

                                  +" DBConnetion object", 30);

      return;

    }//if

    else

    {

      //check the paramter - serialNumber which will be keep in calling method

      //if it is as same as the object's checkoutserial number.

      //if it is same return it. If it is not same, maybe the connection already

      // was returned ealier.

      MetaCatUtil.debugMessage("serial number in Connection: "

                                      +conn.getCheckOutSerialNumber(), 40);

      MetaCatUtil.debugMessage("serial number in local: "+serialNumber, 40);

      if (conn.getCheckOutSerialNumber() == serialNumber)

      {

        dbConn = (DBConnection) connectionPool.elementAt(index);

        //set status to free

        dbConn.setStatus(FREE);

        //count connection time

        dbConn.setConnectionTime

                          (System.currentTimeMillis()-dbConn.getCheckOutTime());

        //set check out time to 0

        dbConn.setCheckOutTime(0);

        MetaCatUtil.debugMessage("Connection: "+dbConn.getTag()+" checked in.",

                                                                        35);

         MetaCatUtil.debugMessage("Connection: "+dbConn.getTag()+"'s status: "

                                                    +dbConn.getStatus(), 35);

      }//if

      else

      {

        MetaCatUtil.debugMessage("This DBConnection couldn't return", 30);

      }//else

    }//else

  }//returnConnection

  /**

   * Given a returned DBConnection, try to find the index of DBConnection object

   * in dbConnection pool by comparing DBConnection' tag and conn.toString.

   * If couldn't find , -1 will be returned.

   * @param conn, the connection need to be found

   */

  private static synchronized int getIndexOfPoolForConnection(DBConnection conn)

  {

    int index = -1;

    String info = null;

    //if conn is null return -1 too

    if (conn==null)

    {

      return -1;

    }

    //get tag of this returned DBConnection

    info = conn.getTag();

    //if the tag is null or empty, -1 will be returned

    if (info==null || info.equals(""))

    {

      return index;

    }

    //compare this info to the tag of every DBConnection in the pool

    for ( int i=0; i< connectionPool.size(); i++)

    {

      DBConnection dbConn = (DBConnection) connectionPool.elementAt(i);

      if (info.equals(dbConn.getTag()))

      {

        index = i;

        break;

      }//if

    }//for

    return index;

  }//getIndexOfPoolForConnection  

  /**

   * Method to shut down all connections

   */

  public static void release()

  {

    //shut down the backgroud recycle thread

    if (DBCONNECTIONRECYCLETHREAD.equals("on"))

    {

      runner.interrupt();

    }

    //cose every dbconnection in the pool

    synchronized(connectionPool)

    {

      for (int i=0;i<connectionPool.size();i++)

      {

        try

        {

          DBConnection dbConn= (DBConnection) connectionPool.elementAt(i);

          dbConn.close();

        }//try

        catch (SQLException e)

        {

          MetaCatUtil.debugMessage("Error in release connection: "

                                            +e.getMessage(), 10);

        }//catch

      }//for

    }//synchronized

  }//release()

  /**

   * periodically to recycle the connection

   */

  public void run()

  {

    DBConnection dbConn = null;

    //keep the thread running

    while (true)

    {

      //check every dbconnection in the pool

      synchronized(connectionPool)

      {

        for (int i=0; i<connectionPool.size(); i++)

        {

          dbConn = (DBConnection) connectionPool.elementAt(i);

          //if a DBConnection conncectioning time for one check out is greater 

          //than 30000 milliseconds print it out

          if (dbConn.getStatus()==BUSY && 

            (System.currentTimeMillis()-dbConn.getCheckOutTime())>=30000)

          {

            MetaCatUtil.debugMessage("This DBConnection is checked out for: "

            +(System.currentTimeMillis()-dbConn.getCheckOutTime())/1000

            +" secs" , 1);

            MetaCatUtil.debugMessage(dbConn.getTag(), 1);

            MetaCatUtil.debugMessage("method: "

                                          +dbConn.getCheckOutMethodName(), 10);

          }

          //check the validation of free connection in the pool

          if (dbConn.getStatus() == FREE)

          {

            try

            {

              //try to print out the warning message for every connection

              if (dbConn.getWarningMessage()!=null)

              {

                MetaCatUtil.debugMessage("Warning for connection "

                  +dbConn.getTag()+" : "+ dbConn.getWarningMessage(), 10);

              }

              //check if it is valiate, if not create new one and replace old one

              if (!validateDBConnection(dbConn))

              {

                MetaCatUtil.debugMessage("Recyle it: "+ dbConn.getTag(), 40);

                //close this DBConnection

                dbConn.close();

                //remove it form connection pool

                connectionPool.remove(i);

                //insert a new DBConnection to same palace

                dbConn = new DBConnection();

                connectionPool.insertElementAt(dbConn, i);

               }//if

            }//try

            catch (SQLException e)

            {

              MetaCatUtil.debugMessage("Error in DBConnectionPool.run: "

                                              +e.getMessage(), 20);

            }//catch

          }//if

        }//for

      }//synchronize   

      //Thread sleep 

      try

      {

        Thread.sleep(CYCLETIMEOFDBCONNECTION);

      }

      catch (Exception e)

      {

        MetaCatUtil.debugMessage("Error in DBConnectionPool.run: "

                                              +e.getMessage(), 20);

      }

    }//while

  }//run

  /**

   * Method to get the number of free DBConnection in DBConnection pool

   */

  public static synchronized int getFreeDBConnectionNumber()

  {

    int numberOfFreeDBConnetion = 0; //return number

    DBConnection db = null; //single DBconnection

    int poolSize = 0; //size of connection pool

    //get the size of DBConnection pool

    poolSize = connectionPool.size();

    //Check every DBConnection in the pool

    for ( int i=0; i<poolSize; i++)

    {

      db = (DBConnection) connectionPool.elementAt(i);

      //check the status of db. If it is free, count it

      if (db.getStatus() == FREE)

      {

        numberOfFreeDBConnetion++;

      }//if

    }//for

    //return the count result

    return numberOfFreeDBConnetion;

  }//getFreeDBConnectionNumber

   /**

   * Method to print out the method name which have busy DBconnection

   */

  public void printMethodNameHavingBusyDBConnection()

  {

    DBConnection db = null; //single DBconnection

    int poolSize = 0; //size of connection pool

    //get the size of DBConnection pool

    poolSize = connectionPool.size();

    //Check every DBConnection in the pool

    for ( int i=0; i<poolSize; i++)

    {

      db = (DBConnection) connectionPool.elementAt(i);

      //check the status of db. If it is free, count it

      if (db.getStatus() == BUSY)

      {

        MetaCatUtil.debugMessage("This method having a busy DBConnection: "

                                    +db.getCheckOutMethodName(), 30);

        MetaCatUtil.debugMessage("The busy DBConnection tag is: "

                                    +db.getTag(), 30);

      }//if

    }//for

  }//printMethodNameHavingBusyDBConnection

  /**

   * Method to decrease dbconnection pool size when all dbconnections are idle

   * If all connections are free and connection pool size greater than 

   * initial value, shrink connection pool size to intital value

   */

  public static synchronized boolean shrinkConnectionPoolSize() 

  {

     int connectionPoolSize = 0; //store the number of dbconnection pool size

     int freeConnectionSize = 0; //store the number of free dbconnection in pool

     int difference = 0; // store the difference number between connection size

                         // and free connection

     boolean hasException = false; //to check if has a exception happend

     boolean result = false; //result

     DBConnection conn = null; // the dbconnection

     connectionPoolSize = connectionPool.size();

     freeConnectionSize = getFreeDBConnectionNumber();

     MetaCatUtil.debugMessage("Connection pool size: " +connectionPoolSize, 3);

     MetaCatUtil.debugMessage("Free Connection number: "+freeConnectionSize, 3);

     difference = connectionPoolSize - freeConnectionSize;

     //If all connections are free and connection pool size greater than 

     //initial value, shrink connection pool size to intital value

     if (difference == 0 && connectionPoolSize > INITIALCONNECTIONNUMBER)

     {

       //db connection having index from  to connectionpoolsize -1

       //intialConnectionnumber should be close and remove from pool

       for ( int i=connectionPoolSize-1; i >= INITIALCONNECTIONNUMBER ; i--)

       {

         //get the dbconnection from pool

         conn = (DBConnection) connectionPool.elementAt(i);

         try

         {

           //close conn

           conn.close();

         }//try

         catch (SQLException e)

         { 

           // set hadException ture

           hasException = true;

           MetaCatUtil.debugMessage("Couldn't close a DBConnection in " +

                            "DBConnectionPool.shrinkDBConnectionPoolSize: " +

                            e.getMessage(), 30);

         }//catch

        //remove it from pool

        connectionPool.remove(i);

        // becuase enter the loop, set result true

        result = true;

       }//for

     }//if

     //if hasException is true ( there at least once exception happend)

     // the result should be false

     if (hasException)

     {

       result =false;

     }//if

     // return result

     return result;

  }//shrinkDBConnectionPoolSize

    /**

   * Method to decrease dbconnection pool size when all dbconnections are idle

   * If all connections are free and connection pool size greater than 

   * initial value, shrink connection pool size to intital value

   */

  public static synchronized void shrinkDBConnectionPoolSize() 

  {

     int connectionPoolSize = 0; //store the number of dbconnection pool size

     int freeConnectionSize = 0; //store the number of free dbconnection in pool

     int difference = 0; // store the difference number between connection size

                         // and free connection

     DBConnection conn = null; // the dbconnection

     connectionPoolSize = connectionPool.size();

     freeConnectionSize = getFreeDBConnectionNumber();

     MetaCatUtil.debugMessage("Connection pool size: " +connectionPoolSize, 3);

     MetaCatUtil.debugMessage("Free Connection number: "+freeConnectionSize, 3);

     difference = connectionPoolSize - freeConnectionSize;

     //If all connections are free and connection pool size greater than 

     //initial value, shrink connection pool size to intital value

     if (difference == 0 && connectionPoolSize > INITIALCONNECTIONNUMBER)

     {

       //db connection having index from  to connectionpoolsize -1

       //intialConnectionnumber should be close and remove from pool

       for ( int i=connectionPoolSize-1; i >= INITIALCONNECTIONNUMBER ; i--)

       {

         //get the dbconnection from pool

         conn = (DBConnection) connectionPool.elementAt(i);

         //make sure again the DBConnection status is free

         if (conn.getStatus()==FREE)

         {

           try

           {

             //close conn

             conn.close();

           }//try

           catch (SQLException e)

           { 

             MetaCatUtil.debugMessage("Couldn't close a DBConnection in " +

                            "DBConnectionPool.shrinkDBConnectionPoolSize: " +

                            e.getMessage(), 30);

           }//catch

           //remove it from pool

           connectionPool.remove(i);

         }//if

       }//for

     }//if

  }//shrinkDBConnectionPoolSize

}//DBConnectionPool