Adding Support for Debugging in a Custom Task

The Integration Services run-time engine enables packages, tasks, and other types of containers to be suspended during execution by using breakpoints. The use of breakpoints lets you review and correct errors that prevent your application or tasks from running correctly. The breakpoint architecture enables the client to evaluate the run-time value of objects in the package at defined points of execution while task processing is suspended.

Custom task developers can use this architecture to create custom breakpoint targets by using the IDTSBreakpointSite interface, and its parent interface, IDTSSuspend. The IDTSBreakpointSite interface defines the interaction between the run-time engine and the task for creating and managing custom breakpoint sites or targets. The IDTSSuspend interface provides methods and properties that are called by the run-time engine to notify the task to suspend or resume its execution.

A breakpoint site or target is a point in the execution of the task where processing can be suspended. Users select from available breakpoint sites in the Set Breakpoints dialog box. For example, in addition to the default breakpoint options, the Foreach Loop Container offers the "Break at the beginning of every iteration of the loop" option.

When a task reaches a breakpoint target during execution, it evaluates the breakpoint target to determine whether a breakpoint is enabled. This indicates that the user wants execution to stop at that breakpoint. If the breakpoint is enabled, the task raises the OnBreakpointHit event to the run-time engine. The run-time engine responds to the event by calling the Suspend method of each task that is currently running in the package. Execution of the task resumes when the runtime calls the ResumeExecution method of the suspended task.

Tasks that do not use breakpoints should still implement the IDTSBreakpointSite and IDTSSuspend interfaces. This ensures that the task is suspended correctly when other objects in the package raise OnBreakpointHit events.

IDTSBreakpointSite Interface and BreakpointManager

Tasks create breakpoint targets by calling the CreateBreakpointTarget method of the BreakpointManager, providing an integer ID and string description as parameters. When the task reaches the point in its code that contains a breakpoint target, it evaluates the breakpoint target by using the IsBreakpointTargetEnabled method to determine whether that breakpoint is enabled. If true, the task notifies the run-time engine by raising the OnBreakpointHit event.

The IDTSBreakpointSite interface defines a single method, AcceptBreakpointManager, which is called by the run-time engine during task creation. This method provides as a parameter the BreakpointManager object, which is then used by the task to create and manage its breakpoints. Tasks should store the BreakpointManager locally for use during the Validate and Execute methods.

The following sample code demonstrates how to create a breakpoint target by using the BreakpointManager. The sample calls the OnBreakpointHit method to raise the event.

public void AcceptBreakpointManager( BreakpointManager breakPointManager )
{
   //   Store the breakpoint manager locally.
   this.bpm  = breakPointManager;
}
public override DTSExecResult Execute( Connections connections,
  Variables variables, IDTSComponentEvents events,
  IDTSLogging log, DtsTransaction txn)
{
   //   Create a breakpoint.
   this.bpm.CreateBreakPointTarget( 1 , "A sample breakpoint target." );
...
   if( this.bpm.IsBreakpointTargetEnabled( 1 ) == true )
      events.OnBreakpointHit( this.bpm.GetBreakpointTarget( 1 ) );
}

Public Sub AcceptBreakpointManager(ByVal breakPointManager As BreakpointManager)

   ' Store the breakpoint manager locally.
   Me.bpm  = breakPointManager

End Sub

Public Overrides Function Execute(ByVal connections As Connections, _
  ByVal variables As Variables, ByVal events As IDTSComponentEvents, _
  ByVal log As IDTSLogging, ByVal txn As DtsTransaction) As DTSExecResult

   ' Create a breakpoint.
   Me.bpm.CreateBreakPointTarget(1 , "A sample breakpoint target.")

   If Me.bpm.IsBreakpointTargetEnabled(1) = True Then
      events.OnBreakpointHit(Me.bpm.GetBreakpointTarget(1))
   End If

End Function

IDTSSuspend Interface

The IDTSSuspend interface defines the methods that are called by the run-time engine when it pauses or resumes execution of a task. The IDTSSuspend interface is implemented by the IDTSBreakpointSite interface, and its Suspend and ResumeExecution methods are usually overridden by the custom task. When the run-time engine receives an OnBreakpointHit event from a task, it calls the Suspend method of each running task, notifying the tasks to pause. When the client resumes execution, the run-time engine calls the ResumeExecution method of the tasks that are suspended.

Suspending and resuming task execution involves pausing and resuming the task's execution thread. In managed code, you do this using the ManualResetEvent class in System.Threading namespace of the .NET Framework.

The following code sample demonstrates suspension and resumption of task execution. Notice that the Execute method has changed from the previous code sample, and the execution thread is paused when firing the breakpoint.

private ManualResetEvent m_suspended = new ManualResetEvent( true );
private ManualResetEvent m_canExecute = new ManualResetEvent( true );
private int   m_suspendRequired = 0;
private int   m_debugMode = 0;

public override DTSExecResult Execute( Connections connections, Variables variables, IDTSComponentEvents events, IDTSLogging log, DtsTransaction txn)
{
   // While a task is not executing, it is suspended.  
   // Now that we are executing,
   // change to not suspended.
   ChangeEvent(m_suspended, false);
   
   // Check for a suspend before doing any work, 
   // in case the suspend and execute calls
   // were initiated at virtually the same time.
   CheckAndSuspend();
   CheckAndFireBreakpoint( componentEvents, 1);
}
private void CheckAndSuspend()
{
   // Loop until we can execute.  
   // The loop is required rather than a simple If
   // because there is a time between the return from WaitOne and the
   // reset that we might receive another Suspend call.  
   // Suspend() will see that we are suspended
   // and return.  So we need to rewait.
   while (!m_canExecute.WaitOne(0, false))
   {
      ChangeEvent(m_suspended, true);
      m_canExecute.WaitOne();
      ChangeEvent(m_suspended, false);
   }
}
private void CheckAndFireBreakpoint(IDTSComponentEvents events, int breakpointID)
{
   // If the breakpoint is enabled, fire it.
   if (m_debugMode != 0 &&    this.bpm.IsBreakpointTargetEnabled(breakpointID))
   {
      //   Enter a suspend mode before firing the breakpoint.  
      //   Firing the breakpoint will cause the runtime 
      //   to call Suspend on this task.  
      //   Because we are blocked on the breakpoint, 
      //   we are suspended.
      ChangeEvent(m_suspended, true);
      events.OnBreakpointHit(this.bpm.GetBreakpointTarget(breakpointID));
      ChangeEvent(m_suspended, false);
   }
   // Check for a suspension for two reasons: 
   //   1. If we are at a point where we could fire a breakpoint, 
   //      we are at a valid suspend point.  Even if we didn't hit a
   //      breakpoint, the runtime may have called suspend, 
   //      so check for it.     
   //   2. Between the return from OnBreakpointHit 
   //      and the reset of the event, it is possible to have
   //      received a suspend call from which we returned because 
   //      we were already suspended.  We need to be sure it is okay
   //      to continue executing now.
   CheckAndSuspend();
}
static void ChangeEvent(ManualResetEvent e, bool shouldSet)
{
   bool succeeded;
   if (shouldSet)
      succeeded = e.Set();
   else
      succeeded = e.Reset();

   if (!succeeded)
      throw new Exception("Synchronization object failed.");
            
}
public bool SuspendRequired
{
   get   {return m_suspendRequired != 0;}
   set
   {
      // This lock is also taken by Suspend().  
      // Because it is possible for the package to be
      // suspended and resumed in quick succession, 
      // this property might be set before
      // the actual Suspend() call.  
      // Without the lock, the Suspend() might reset the canExecute
      // event after we set it to abort the suspension.
      lock (this)
      {
         Interlocked.Exchange(ref m_suspendRequired, value ? 1 : 0);
         if (!value)
            ResumeExecution();
      }
   }
}
public void ResumeExecution()
{
   ChangeEvent( m_canExecute,true );
}
public void Suspend()
{
   // This lock is also taken by the set SuspendRequired method.  
   // It prevents this call from overriding an 
   // aborted suspension.  See comments in set SuspendRequired.
   lock (this)
   {
      // If a Suspend is required, do it.
      if (m_suspendRequired != 0)
         ChangeEvent(m_canExecute, false);
   }
   // We can't return from Suspend until the task is "suspended".
   // This can happen one of two ways: 
   // the m_suspended event occurs, indicating that the execute thread
   // has suspended, or the canExecute flag is set, 
   // indicating that a suspend is no longer required.
   WaitHandle [] suspendOperationComplete = {m_suspended, m_canExecute};
   WaitHandle.WaitAny(suspendOperationComplete);
}

Private m_suspended As ManualResetEvent = New ManualResetEvent(True)
Private m_canExecute As ManualResetEvent = New ManualResetEvent(True)
Private m_suspendRequired As Integer = 0
Private m_debugMode As Integer = 0

Public Overrides Function Execute(ByVal connections As Connections, _
ByVal variables As Variables, ByVal events As IDTSComponentEvents, _
ByVal log As IDTSLogging, ByVal txn As DtsTransaction) As DTSExecResult

   ' While a task is not executing it is suspended.  
   ' Now that we are executing,
   ' change to not suspended.
   ChangeEvent(m_suspended, False)

   ' Check for a suspend before doing any work, 
   ' in case the suspend and execute calls
   ' were initiated at virtually the same time.
   CheckAndSuspend()
   CheckAndFireBreakpoint(componentEvents, 1)

End Function

Private Sub CheckAndSuspend()

   ' Loop until we can execute.  
   ' The loop is required rather than a simple if
   ' because there is a time between the return from WaitOne and the
   ' reset that we might receive another Suspend call.  
   ' Suspend() will see that we are suspended
   ' and return.  So we need to rewait.
   Do While Not m_canExecute.WaitOne(0, False)
              ChangeEvent(m_suspended, True)
              m_canExecute.WaitOne()
              ChangeEvent(m_suspended, False)
   Loop

End Sub

Private Sub CheckAndFireBreakpoint(ByVal events As IDTSComponentEvents, _
ByVal breakpointID As Integer)

   ' If the breakpoint is enabled, fire it.
   If m_debugMode <> 0 AndAlso Me.bpm.IsBreakpointTargetEnabled(breakpointID) Then
              '   Enter a suspend mode before firing the breakpoint.  
              '   Firing the breakpoint will cause the runtime 
              '   to call Suspend on this task.  
              '   Because we are blocked on the breakpoint, 
              '   we are suspended.
              ChangeEvent(m_suspended, True)
              events.OnBreakpointHit(Me.bpm.GetBreakpointTarget(breakpointID))
              ChangeEvent(m_suspended, False)
   End If

   ' Check for a suspension for two reasons: 
   '   1. If we are at a point where we could fire a breakpoint, 
   '         we are at a valid suspend point.  Even if we didn't hit a
   '         breakpoint, the runtime may have called suspend, 
   '         so check for it.   
   '   2. Between the return from OnBreakpointHit 
   '         and the reset of the event, it is possible to have
   '         received a suspend call from which we returned because 
   '         we were already suspended.  We need to be sure it is okay
   '         to continue executing now.
   CheckAndSuspend()

End Sub

Shared Sub ChangeEvent(ByVal e As ManualResetEvent, ByVal shouldSet As Boolean)

   Dim succeeded As Boolean
   If shouldSet Then
              succeeded = e.Set()
   Else
              succeeded = e.Reset()
   End If

   If (Not succeeded) Then
              Throw New Exception("Synchronization object failed.")
   End If
 
End Sub

Public Property SuspendRequired() As Boolean
   Get
               Return m_suspendRequired <> 0
  End Get
  Set
    ' This lock is also taken by Suspend().  
     '   Because it is possible for the package to be
     '   suspended and resumed in quick succession, 
     '   this property might be set before
     '   the actual Suspend() call.  
     '   Without the lock, the Suspend() might reset the canExecute
     '   event after we set it to abort the suspension.
              SyncLock Me
                         Interlocked.Exchange(m_suspendRequired,IIf(Value, 1, 0))
                         If (Not Value) Then
                                    ResumeExecution()
                         End If
              End SyncLock
   End Set
End Property

Public Sub ResumeExecution()
   ChangeEvent(m_canExecute,True)
End Sub

Public Sub Suspend()

   ' This lock is also taken by the set SuspendRequired method.  
   ' It prevents this call from overriding an 
   ' aborted suspension.  See comments in set SuspendRequired.
   SyncLock Me
   ' If a Suspend is required, do it.
              If m_suspendRequired <> 0 Then
                         ChangeEvent(m_canExecute, False)
              End If
   End SyncLock
   ' We can't return from Suspend until the task is "suspended".
   ' This can happen one of two ways: 
   ' the m_suspended event occurs, indicating that the execute thread
   ' has suspended, or the canExecute flag is set, 
   ' indicating that a suspend is no longer required.
   Dim suspendOperationComplete As WaitHandle() = {m_suspended, m_canExecute}
   WaitHandle.WaitAny(suspendOperationComplete)

End Sub

See Also

Tasks

Debugging Control Flow