DB2®Command.Cancel Method

Attempts to cancel the execution of a DB2Command.

Namespace:: IBM.Data.DB2
Assembly:: IBM.Data.DB2 (in IBM.Data.DB2.dll)

Syntax


[Visual Basic]
NotOverridable Public Sub Cancel()
[C#]
public void Cancel();
[C++]
public: __sealed void Cancel();
[JScript]
public function Cancel();

Remarks

If there is nothing to cancel, nothing happens. However, if there is a command in process, and the attempt to cancel fails, no exception is generated.

Example

The following example creates two threads, one thread for running the long query and another thread for canceling the long query after waiting for 5 seconds. To accomplish this, the method is passed a connection string which is used to connect to the database.

Here is the Visual Basic code for this task:


Public Sub CreateMyDB2Command _
(ByVal myConnectionString As String)
    Dim mySelectQuery As String = "select * from emp, dept, empact"
    Dim myConnection As New DB2Connection(myConnectionString)
    Dim myCommand As New DB2Command(mySelectQuery, myConnection)
    Dim cmdThread As New Thread(AddressOf do_Cmd)         
    Dim cancelThread As New Thread(AddressOf do_Cancel)         
    
    myCommand.Connection.Open()         
    Console.WriteLine("Starting the command thread")         
    cmdThread = New Thread(New ParameterizedThreadStart(AddressOf do_Cmd))         
    cmdThread.Start(myCommand)         
    
    Console.WriteLine("Starting the cancel thread")        
    cancelThread = New Thread(New ParameterizedThreadStart(AddressOf do_Cancel))        
    cancelThread.Start(myCommand)         
    
    cmdThread.Join()         
    cancelThread.Join()     
End Sub     

Public Sub do_Cancel(ByVal data As Object)         
    Dim cmd As New DB2Command()         
    cmd = data         
    'sleep for 5 seconds before starting to cancel the command         
    Thread.Sleep(5000)         
    Try
       cmd.Cancel()             
       Console.WriteLine("SQL command cancelled")         
    Catch ex As Exception                        
       Console.WriteLine(ex.Message)         
    End Try     
End Sub     

Public Sub do_Cmd(ByVal data As Object)         
    Dim cmd As New DB2Command()         
    Dim reader As DB2DataReader         
    cmd = data  
    Console.WriteLine("Running a long query ...")         
    Try        
        reader = cmd.ExecuteReader()             
        While (reader.Read())      
          Console.WriteLine(reader.GetString(0) + "  " + reader.GetString(1))  
        End While             
        Console.WriteLine("Query finished")  
        reader.Close()         
    Catch ex As Exception              
        Console.WriteLine(ex.Message)         
    End Try 
End Sub

Here is the C # code for this task:


public void CreateMyDB2Command(string myConnectionString)
{
   string mySelectQuery = "select * from emp, dept, empact";
   DB2Connection myConnection = new DB2Connection(myConnectionString);
   DB2Command myCommand = new DB2Command(mySelectQuery, myConnection);
   myCommand.Connection.Open();    
  
   System.Console.WriteLine("Starting the command thread");    
   Thread cmdThread = new Thread(new ParameterizedThreadStart(do_Cmd));    
   cmdThread.Start(myCommand);    

   System.Console.WriteLine("Starting the cancel thread");    
   Thread cancelThread = new Thread(new ParameterizedThreadStart(do_Cancel));  
   cancelThread.Start(myCommand);        

   cmdThread.Join();  
   cancelThread.Join(); 
}
public static void do_Cancel(object data)     
    {      
    DB2Command cmd = (DB2Command)data;       
    // sleep for 5 seconds before starting to cancel the command       
    Thread.Sleep(5000);         
    try       
    {  
       cmd.Cancel();          
       System.Console.WriteLine("SQL command cancelled");       
    }       
    catch (Exception ex)       
    {                      
       Console.WriteLine(ex.Message);       
    }  
}  

public static void do_Cmd(object data)     
    {            
     DB2Command cmd = (DB2Command)data;                 
     System.Console.WriteLine("Running a long query ...");         
     try         
     {             
        DB2DataReader reader = cmd.ExecuteReader();             
        while (reader.Read())      
        {                 
           System.Console.WriteLine(reader.GetString(0) + "  " + reader.GetString(1));                             
        }          
        System.Console.WriteLine("Query finished");             
        reader.Close();
      }         
      catch (Exception ex)         
      {            
        Console.WriteLine(ex.Message);         
      }
}

Note: DB2Command.Cancel will not close the cursor associated with the reader object (such as DB2DataReader or DB2ResultSet) created by using the DB2Command object. The application need to call the Close method on the reader object in order to release database resources associated with the reader object.