Question

JI have written a .NET C# Windows Form app in Visual Studio 2008 that uses a Semaphore to run multiple jobs as threads when the Start button is pressed.

It’s experiencing an issue where the Form goes into a comma after being run for 40 minutes or more. The log files indicate that the current jobs complete, it picks a new job from the list, and there it hangs.

I have noticed that the Windows Form becomes unresponsive when this happens. The form is running in its own thread.

This is a sample of the code I am using:

protected void ProcessJobsWithStatus (Status status)
        {
int maxJobThreads = Convert.ToInt32(ConfigurationManager.AppSettings["MaxJobThreads"]);
            Semaphore semaphore = new Semaphore(maxJobThreads, maxJobThreads);  // Available=3; Capacity=3


            int threadTimeOut = Convert.ToInt32(ConfigurationManager.AppSettings["ThreadSemaphoreWait"]);//in Seconds
            //gets a list of jobs from a DB Query.
List<Job> jobList = jobQueue.GetJobsWithStatus(status);
            //we need to create a list of threads to check if they all have stopped.
            List<Thread> threadList = new List<Thread>();
            if (jobList.Count > 0)
            {
                foreach (Job job in jobList)
                {
                    logger.DebugFormat("Waiting green light for JobId: [{0}]", job.JobId.ToString());
                    if (!semaphore.WaitOne(threadTimeOut * 1000))
                    {
                        logger.ErrorFormat("Semaphore Timeout. A thread did NOT complete in time[{0} seconds]. JobId: [{1}] will start", threadTimeOut, job.JobId.ToString());

                    }

                    logger.DebugFormat("Acquired green light for JobId: [{0}]", job.JobId.ToString());
                    // Only N threads can get here at once    
                    job.semaphore = semaphore;
                    ThreadStart threadStart = new ThreadStart(job.Process);

                    Thread thread = new Thread(threadStart);
                    thread.Name = job.JobId.ToString();
                    threadList.Add(thread);
                    thread.Start();


                }

                logger.Info("Waiting for all threads to complete");

                //check that all threads have completed.
                foreach (Thread thread in threadList)
                {
                    logger.DebugFormat("About to join thread(jobId): {0}", thread.Name);
                    if (!thread.Join(threadTimeOut * 1000))
                    {
                        logger.ErrorFormat("Thread did NOT complete in time[{0} seconds]. JobId: [{1}]", threadTimeOut, thread.Name);
                    }
                    else {
                        logger.DebugFormat("Thread did complete in time. JobId: [{0}]", thread.Name);
                    }
                }                   

            }

            logger.InfoFormat("Finished Processing Jobs in Queue with status [{0}]...", status);

}

//form methods

private void button1_Click(object sender, EventArgs e)
        {
            buttonStop.Enabled = true;
            buttonStart.Enabled = false;

            ThreadStart threadStart = new ThreadStart(DoWork);
            workerThread = new Thread(threadStart);

            serviceStarted = true;
            workerThread.Start();



        }

private void DoWork()
        {
            EmailAlert emailAlert = new EmailAlert ();
            // start an endless loop; loop will abort only when "serviceStarted" flag = false
            while (serviceStarted)
            {  
                emailAlert.ProcessJobsWithStatus(0);

                // yield
                if (serviceStarted)
                {
                    Thread.Sleep(new TimeSpan(0, 0, 1));
                }
            }

            // time to end the thread
            Thread.CurrentThread.Abort();
        }

//job.process()

 public void Process()
        {
             try
            {

                //sets the status, DateTimeStarted, and the processId
                this.UpdateStatus(Status.InProgress);

                //do something

                logger.Debug("Updating Status to [Completed]");

                //hits, status,DateFinished
                this.UpdateStatus(Status.Completed);

            }
            catch (Exception e)
            {
                logger.Error("Exception: " + e.Message);
                this.UpdateStatus(Status.Error);

            }
            finally {
                logger.Debug("Relasing semaphore");
                semaphore.Release();
            }

I have tried to log what I can into a file to detect where the problem is happening, but so far I haven’t been able to identify where this happens. Losing control of the Windows Form makes me think that this has nothing to do with processing the jobs. Any ideas?

Solution: Profiling it with RedGate ANTS was producing the issue. It does not happen when run directly.

Answer 1

The first thing I see is your Thread.CurrentThread.Abort() call. This is unnecessary. Let the function exit and the thread will shut down gracefully.

The second thing I noticed is that even if a timeout occurs for acquiring a semaphore a thread will be created anyway. Your form could be hanging as a result of too many threads.

logger.DebugFormat("Waiting green light for JobId: [{0}]", job.JobId.ToString());
if (!semaphore.WaitOne(threadTimeOut * 1000))
{
   logger.ErrorFormat("Semaphore Timeout. A thread did NOT complete in time[{0} seconds]. JobId: [{1}] will start", threadTimeOut, job.JobId.ToString());
   // Should have exit here.
}
logger.DebugFormat("Acquired green light for JobId: [{0}]", job.JobId.ToString());

The third thing is your worker thread is calling a function which simply creates threads for every job in the jobs loop. If a job doesn’t complete (assuming this causes a job to be removed from the queue since I don’t see that code anywhere.) before DoWork wakes up from it’s sleep it’s going to iterate over the same Job and try to create another thread for it.