I have tried but it is not working i want to stop and pause this task:: code below

private void checkingTimer()
        {
            System.Windows.Threading.DispatcherTimer dispatcherTimer = new System.Windows.Threading.DispatcherTimer();
            dispatcherTimer.Tick  = new EventHandler(startPollingAwaitingURLs);
            dispatcherTimer.Interval = new TimeSpan(0, 0, 0, 0, 1000);
            dispatcherTimer.Start();
        }

        private static object _lock_CrawlingSync = new object();
        private static bool blBeingProcessed = false;
        private static List<Task> lstCrawlingTasks = new List<Task>();
        private static List<string> lstCurrentlyCrawlingUrls = new List<string>();
        private void btnTest_Click(object sender, RoutedEventArgs e)
        {
            using (WebCrawlerEntities1 db = new WebCrawlerEntities1())
            {
                db.tblMainUrls.RemoveRange(db.tblMainUrls);
                db.SaveChanges();
            }
        }


        private void clearDBandStart(object sender, RoutedEventArgs e)
        {
            dtStartDate = DateTime.Now;
          
            crawlPage(urlTextbox.Text.normalizeUrl(), 0, urlTextbox.Text.normalizeUrl(), DateTime.Now);
            checkingTimer();
        }

        private void startPollingAwaitingURLs(object sender, EventArgs e)
        {
            lock (UserLogs)
            {
                string srPerMinCrawlingspeed = (irCrawledUrlCount.ToDouble() / (DateTime.Now - dtStartDate).TotalMinutes).ToString("N2");

                string srPerMinDiscoveredLinkSpeed = (irDiscoveredUrlCount.ToDouble() / (DateTime.Now - dtStartDate).TotalMinutes).ToString("N2");

                string srPassedTime = (DateTime.Now - dtStartDate).TotalMinutes.ToString("N2");

                UserLogs.Insert(0, $"{DateTime.Now} polling awaiting urls \t processing: {blBeingProcessed} \t number of crawling tasks: {lstCrawlingTasks.Count}");

                UserLogs.Insert(0, $"Total Time: {srPassedTime} Minutes \t Total Crawled Links Count: {irCrawledUrlCount.ToString("N0")} \t Crawling Speed Per Minute: {srPerMinCrawlingspeed} \t Total Discovered Links : {irDiscoveredUrlCount.ToString("N0")} \t Discovered Url Speed: {srPerMinDiscoveredLinkSpeed} ");
            }

            logMesssage($"polling awaiting urls \t processing: {blBeingProcessed} \t number of crawling tasks: {lstCrawlingTasks.Count}");

            if (blBeingProcessed)
                return;

            lock (_lock_CrawlingSync)
            {
                
                blBeingProcessed = true;

                lstCrawlingTasks = lstCrawlingTasks.Where(pr => pr.Status != TaskStatus.RanToCompletion && pr.Status != TaskStatus.Faulted).ToList();

                int irTasksCountToStart = _irNumberOfTotalConcurrentCrawling - lstCrawlingTasks.Count;

                if (irTasksCountToStart > 0)
                    using (WebCrawlerEntities1 db = new WebCrawlerEntities1())
                    {
                        var vrReturnedList = db.tblMainUrls.Where(x => x.isCrawled == false && x.CrawlTryCounter < _irMaximumTryCount)
                                  .OrderBy(pr => pr.DiscoverDate)
                            .Select(x => new
                            {
                                x.Url,
                                x.LinkDepthLevel
                            }).Take(irTasksCountToStart * 2).ToList();

                        logMesssage(string.Join(" , ", vrReturnedList.Select(pr => pr.Url)));

                        foreach (var vrPerReturned in vrReturnedList)
                        {
                            var vrUrlToCrawl = vrPerReturned.Url;
                            int irDepth = vrPerReturned.LinkDepthLevel;
                            lock (lstCurrentlyCrawlingUrls)
                            {
                                if (lstCurrentlyCrawlingUrls.Contains(vrUrlToCrawl))
                                {
                                    logMesssage($"bypass url since already crawling: \t {vrUrlToCrawl}");
                                    continue;
                                }
                                lstCurrentlyCrawlingUrls.Add(vrUrlToCrawl);
                            }

                            logMesssage($"starting crawling url: \t {vrUrlToCrawl}");

                            lock (UserLogs)
                            {
                                UserLogs.Insert(0, $"{DateTime.Now} starting crawling url: \t {vrUrlToCrawl}");
                            }

                            var vrStartedTask = Task.Factory.StartNew(() => { crawlPage(vrUrlToCrawl, irDepth, null, DateTime.MinValue); }).ContinueWith((pr) =>
                            {

                                lock (lstCurrentlyCrawlingUrls)
                                {
                                    lstCurrentlyCrawlingUrls.Remove(vrUrlToCrawl);
                                    logMesssage($"removing url from list since task completed: \t {vrUrlToCrawl}");
                                }

                            });
                            lstCrawlingTasks.Add(vrStartedTask);

                            if (lstCrawlingTasks.Count > _irNumberOfTotalConcurrentCrawling)
                                break;
                        }
                    }

                blBeingProcessed = false;
            }
        }

so is there a way to stop my task up ahead and pause should i mre.set() or .Set()

my application is a web crawler that get links from any website.

so when pressing on a button web crawling task pause or stop and restart ... any methods to do or changes

CodePudding user response：

Try :

• Thread.Sleep() to pause your task.
• Thread.Interrupt() to stop your sleeping task.

CodePudding user response：

Technically you can't stop a Task. Task isn't running anything but only waiting for a completion of something it was bound for. You can stop the code, running in the Thread. For example, with ManualResetEventSlim.

private readonly ManualResetEventSlim _mre = new ManualResetEventSlim(true); // not paused initially

public void Pause()
{
    _mre.Reset();
}

public void Resume()
{
    _mre.Set();
}

In the method where you want to pause the execution when requested, just add.

_mre.Wait();

Few tips

• Use Task.Run instead of Task.Factory.StartNew and learn the difference.
• Find something about Producer/Consumer programming pattern and related thread-safe collections.
• Say hello to Asynchronous programming.