Question

Aborting Threads in C# avoiding Thread.Abort()

Asked by: SINCO

I'm using a BackgroundWorker which, when run, runs through a queue of delegates and invokes each one, which carries out automation on a robot.  If the user wants to abort this automation at any stage all movement and operation on the robot needs to be stopped immediately.  You would think that Thread.Abort() would work nicely, as this should stop the thread that is invoking the delegates.  However, this causes all kinds of programming issues and a quick look on Google has shown me that using Thread.Abort() is not recommended.  Also the BackgroundWorker.CancelAsync() method is not suitable as it waits for a safe point to cancel the thread, which is simply not responsive enough.

What I guess would be the ultimate solution is to have an abort event that when triggered (on abort) stops any active delegate and exits the iteration of the queue that invokes them, thus letting the thread end gracefully.

Is there a way to stop a delegate that has been invoked, and cancel any remaining methods that it contains, without each method (within the delegate) itself having access to a Boolean which contains whether it should be run or not?

I have included the code that invokes my queue of delegates to hopefully make this a bit clearer.

Hope this all makes sense and someone can help!

/// <summary>
        /// Run the program
        /// </summary>
        /// <returns></returns>
        private EFeedback doProgramRun()
        {
            // disply message
            DataMonitor.WriteLine("Running the RoToR program...");
 
            // assign threadname
            Thread.CurrentThread.Name = ProgramName;
 
            // display thread attributes
            DataMonitor.WriteLine("Thread ID for this worker ({0}) is: 0x{1}", Thread.CurrentThread.Name, Convert.ToString(Thread.CurrentThread.ManagedThreadId,16));
 
            // also set this threads priority to maxmimum
            Thread.CurrentThread.Priority = ThreadPriority.Highest;
 
            // capture a refernce to this programs worker thread
            thisProgramWorkerThread = Thread.CurrentThread;
 
            // increment run counter
            ProgramsRun++;
 
            // get program start time
            DateTime programStartTime = DateTime.Now;
 
            try
            {
                // reset complete routines count
                this.completedRoutines = 0;
 
                // for each routine in program queue
                foreach (IRoToRRoutine currentMethod in this.ProgramQueue)
                {
                    // get the current time
                    DateTime routineStartTime = DateTime.Now;
 
                    // run the method - returning feedback to data monitor 
                    DataMonitor.Monitor(currentMethod.ReturnDelegation().Invoke());
 
                    // display how long it took
                    DataMonitor.WriteLine("Routine took {0}", DateTime.Now - routineStartTime);
 
                    // add a line so that routines appear seperate
                    DataMonitor.InsertConsoleBreak();
 
                    // increment completed routines
                    this.completedRoutines++;
 
                    // check for subscribers to event
                    if (this.RoutineComplete != null)
                    {
                        // dispatch event
                        this.RoutineComplete(new CommunicationEventArgs());
                    }
                }
 
                // if program completed ok
                if (!wasCancelled)
                {
                    // display message
                    DataMonitor.WriteLine("RoToR program complete in {0}", DateTime.Now - programStartTime);
 
                    // increment complete counter
                    ProgramsComplete++;
 
                    // return complete
                    return EFeedback.Complete;
                }
                else
                {
                    // return abort
                    return EFeedback.Abort;
                }
 
            }
            catch (Exception e)
            {
                // display error
                DataMonitor.WriteLine(" -RoToR program error detected: {0}", e.Message);
 
                // increment error counter
                ProgramsError++;
 
                // return error
                return EFeedback.Error;
            }
            finally
            {
                // unsubscribe event handlers - because garbage collector may not collect for a while
                this.uninstallEventHandlers();
                // always for disposal of worker before garbage collector
                this.programWorker.Dispose();
            }
        }

                                  
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Asked On
2009-03-25 at 05:37:26ID24262892
Tags

C#

,

Thread

,

Thread.Abort()

Topics

C / C++ / C# Editors and IDEs

,

Automation

Participating Experts
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Points
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Comments
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Answers

 

by: taliesin1977Posted on 2009-03-25 at 13:49:21ID: 23984537

I am not sure if this is a problem for .NET 2.0 and later. It sounds like for .NET 2.0 and later the ThreadAbortException is delayed until the end of a finally block if it occurs in the finally block.

See the comment by cbeyls at the end of this page:
http://dotnet.org.za/ernst/archive/2004/03/15/736.aspx

 

by: SINCOPosted on 2009-04-02 at 07:51:09ID: 24050456

Thanks, although I think that just due to the nature of Thread.Abort() it does still cause issues.

To be a bit clearer, the problem is showing itself only when the the thread is re allocated, and not when it is aborted.  It seems that once you abort, the system works fine, and then when a new thread is needed and the framework allocates one a 'random' exception is thrown.  I just cant find a clean way of killing a thread as instantly as possible (BackgroundWorker CancelPending is just not responsive enough).

20120131-EE-VQP-002

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