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Use Try and Finally on Disposable Resources

Why

Using a try/finally block ensures that resources are disposed even if an exception occurs. Not disposing resources properly leads to performance degradation over time. 

When

This is important guideline when working with disposable resources such as 

  • Database connections 
  • File handles 
  • Message queue handles 
  • Text reader, writer 
  • Binary reader, writer 
  • Crypto stream 
  • Symmetric, Asymmetric and Hash algorithms. 
  • Windows Identity, Windows Impersonation Context  
  • Timer, Wait Handle in case of threading 
  • Impersonation Context 
  • XML Reader 
  • XML Writer

How

The following code fragment demonstrates disposing resources in a finally block..

SqlConnection conn = new SqlConnection(...)

try

{

   conn.Open();

   ...

}

finally

{

   if(null != conn)

     conn.close();

}

If developing in C# you can use the 'using' keyword which will automatically dispose resources after their usage.

using(SqlConnection conn = new SqlConnection(...))

{

   conn.Open();   

   ....

}


Problem Example

A database connection is opened and used to access data. 

Unfortunately, if there is an exception other than SqlException or if the exception handling code itself throws an exception the database connection won't be closed. This failure to close database connections could cause the application to run out of database connection impacting application performance.

try

{

   conn.Open();

   // do something with the connection

   // some more processing

   // close the connection

   if(conn != null)

     conn.Close();

}

catch(SqlException ex)

{

   // do exception handling

   // close the connection

   if(conn != null)

     conn.Close();

}

Solution Example

A database connection is opened and used to access data. The finally block will be executed whether there is exception or not, ensuring that the database connection is closed. 

SqlConnection conn = new SqlConnection(...)

try

{

   conn.Open();

   // do something with the connection

   // some more processing

}

catch(SqlException ex)

{

   // do exception handling 

  

}

finally

{

   // close the connection

   if(conn != null)

     conn.Close();

}

 

 

Additional Resources

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