SERVLET.SYN

Minimize synchronization in Servlets

Description

This rule flags excessive synchronization in servlets.

Servlets are multi-threaded. Servlet-based applications have to recognize and handle this. However, if large sections of code are synchronized, an application effectively becomes single threaded, and throughput decreases.

Example

 package SERVLET;
 
 import javax.servlet.*;
 import javax.servlet.http.*;
 import java.sql.*;
 
 public class SYN extends HttpServlet {
     private int numberOfRows = 0;
     private javax.sql.DataSource ds = null;
 
     public void synExample (HttpServletRequest request) {
         Connection conn = null;
         ResultSet rs = null;
         PreparedStatement stmt = null;
         int startingRows;
 
         try {
             synchronized (this) {
                 startingRows = numberOfRows;
                 String info = null;
                 conn = ds.getConnection ("db2admin", "db2admin");
                 stmt = conn.prepareStatement ("select * from
db2admin.employy");
                 rs = stmt.executeQuery ();
                 info = rs.getString ("Name");
             }
         } catch (Exception e) {
         } finally {
              try { rs.close (); }
              catch (Exception e) {}
         }
     }
 }

Repair

 public void synBetterExample (HttpServletRequest request) {
         Connection conn = null;
         ResultSet rs = null;
         PreparedStatement stmt = null;
         int startingRows;
 
         // lock only necessary one.
         synchronized (this) {
             startingRows = numberOfRows;
         }
 
         try {
             String info = null;
             conn = ds.getConnection ("db2admin", "db2admin");
             stmt = conn.prepareStatement ("select * from
db2admin.employy");
             rs = stmt.executeQuery ();
             info = rs.getString ("Name");
          } catch (Exception e) {
          } finally {
              try { rs.close (); }
              catch (Exception e) {}
          }
     }

Reference

IBM WebSphere Application Server Standard and Advanced Editions, Harvey W. Gunther.

http://www-4.ibm.com/software/webservers/appserv/ws_bestpractices.pdf