Use Task.Yield to avoid using Parallel.For

Author: taooceros

Flow.Launcher/ViewModel/MainViewModel.cs

@@ -86,7 +86,7 @@ private void RegisterResultsUpdatedEvent()
         {
             foreach (var pair in PluginManager.GetPluginsForInterface<IResultUpdated>())
             {
-                var plugin = (IResultUpdated)pair.Plugin;
+                var plugin = (IResultUpdated) pair.Plugin;
                 plugin.ResultsUpdated += (s, e) =>
                 {
                     Task.Run(() =>
@@ -113,25 +113,13 @@ private void InitializeKeyCommands()
                 }
             });
 
-            SelectNextItemCommand = new RelayCommand(_ =>
-            {
-                SelectedResults.SelectNextResult();
-            });
+            SelectNextItemCommand = new RelayCommand(_ => { SelectedResults.SelectNextResult(); });
 
-            SelectPrevItemCommand = new RelayCommand(_ =>
-            {
-                SelectedResults.SelectPrevResult();
-            });
+            SelectPrevItemCommand = new RelayCommand(_ => { SelectedResults.SelectPrevResult(); });
 
-            SelectNextPageCommand = new RelayCommand(_ =>
-            {
-                SelectedResults.SelectNextPage();
-            });
+            SelectNextPageCommand = new RelayCommand(_ => { SelectedResults.SelectNextPage(); });
 
-            SelectPrevPageCommand = new RelayCommand(_ =>
-            {
-                SelectedResults.SelectPrevPage();
-            });
+            SelectPrevPageCommand = new RelayCommand(_ => { SelectedResults.SelectPrevPage(); });
 
             SelectFirstResultCommand = new RelayCommand(_ => SelectedResults.SelectFirstResult());
 
@@ -209,6 +197,7 @@ private void InitializeKeyCommands()
         public ResultsViewModel History { get; private set; }
 
         private string _queryText;
+
         public string QueryText
         {
             get { return _queryText; }
@@ -229,10 +218,12 @@ public void ChangeQueryText(string queryText)
             QueryTextCursorMovedToEnd = true;
             QueryText = queryText;
         }
+
         public bool LastQuerySelected { get; set; }
         public bool QueryTextCursorMovedToEnd { get; set; }
 
         private ResultsViewModel _selectedResults;
+
         private ResultsViewModel SelectedResults
         {
             get { return _selectedResults; }
@@ -264,6 +255,7 @@ private ResultsViewModel SelectedResults
                         QueryText = string.Empty;
                     }
                 }
+
                 _selectedResults.Visbility = Visibility.Visible;
             }
         }
@@ -324,7 +316,7 @@ private void QueryContextMenu()
                     var filtered = results.Where
                     (
                         r => StringMatcher.FuzzySearch(query, r.Title).IsSearchPrecisionScoreMet()
-                            || StringMatcher.FuzzySearch(query, r.SubTitle).IsSearchPrecisionScoreMet()
+                             || StringMatcher.FuzzySearch(query, r.SubTitle).IsSearchPrecisionScoreMet()
                     ).ToList();
                     ContextMenu.AddResults(filtered, id);
                 }
@@ -351,7 +343,7 @@ private void QueryHistory()
                     Title = string.Format(title, h.Query),
                     SubTitle = string.Format(time, h.ExecutedDateTime),
                     IcoPath = "Images\\history.png",
-                    OriginQuery = new Query { RawQuery = h.Query },
+                    OriginQuery = new Query {RawQuery = h.Query},
                     Action = _ =>
                     {
                         SelectedResults = Results;
@@ -397,7 +389,8 @@ private void QueryResults()
 
                     _lastQuery = query;
                     Task.Delay(200, currentCancellationToken).ContinueWith(_ =>
-                    { // start the progress bar if query takes more than 200 ms and this is the current running query and it didn't finish yet
+                    {
+                        // start the progress bar if query takes more than 200 ms and this is the current running query and it didn't finish yet
                         if (currentUpdateSource == _updateSource && _isQueryRunning)
                         {
                             ProgressBarVisibility = Visibility.Visible;
@@ -410,17 +403,14 @@ private void QueryResults()
                         // so looping will stop once it was cancelled
 
                         Task[] tasks = new Task[plugins.Count];
-                        var parallelOptions = new ParallelOptions { CancellationToken = currentCancellationToken };
                         try
                         {
-                            Parallel.For(0, plugins.Count, parallelOptions, i =>
+                            for (var i = 0; i < plugins.Count; i++)
                             {
                                 if (!plugins[i].Metadata.Disabled)
-                                {
                                     tasks[i] = QueryTask(plugins[i], query, currentCancellationToken);
-                                }
                                 else tasks[i] = Task.CompletedTask; // Avoid Null
-                            });
+                            }
 
                             // Check the code, WhenAll will translate all type of IEnumerable or Collection to Array, so make an array at first
                             await Task.WhenAll(tasks);
@@ -434,20 +424,25 @@ private void QueryResults()
                         // until the end of all querying
                         _isQueryRunning = false;
                         if (!currentCancellationToken.IsCancellationRequested)
-                        { // update to hidden if this is still the current query
+                        {
+                            // update to hidden if this is still the current query
                             ProgressBarVisibility = Visibility.Hidden;
                         }
 
                         // Local Function
                         async Task QueryTask(PluginPair plugin, Query query, CancellationToken token)
                         {
+                            // Since it is wrapped within a Task.Run, the synchronous context is null
+                            // Task.Yield will force it to run in ThreadPool
+                            await Task.Yield();
+
                             var results = await PluginManager.QueryForPlugin(plugin, query, token);
                             if (!currentCancellationToken.IsCancellationRequested)
                                 UpdateResultView(results, plugin.Metadata, query);
                         }
-
-                    }, currentCancellationToken).ContinueWith(t => Log.Exception("|MainViewModel|Plugins Query Exceptions", t.Exception),
-                                                              TaskContinuationOptions.OnlyOnFaulted);
+                    }, currentCancellationToken).ContinueWith(
+                        t => Log.Exception("|MainViewModel|Plugins Query Exceptions", t.Exception),
+                        TaskContinuationOptions.OnlyOnFaulted);
                 }
             }
             else
@@ -514,6 +509,7 @@ private Result ContextMenuTopMost(Result result)
                     }
                 };
             }
+
             return menu;
         }
 
@@ -559,6 +555,7 @@ private bool HistorySelected()
             var selected = SelectedResults == History;
             return selected;
         }
+
         #region Hotkey
 
         private void SetHotkey(string hotkeyStr, EventHandler<HotkeyEventArgs> action)
@@ -577,7 +574,8 @@ private void SetHotkey(HotkeyModel hotkey, EventHandler<HotkeyEventArgs> action)
             catch (Exception)
             {
                 string errorMsg =
-                    string.Format(InternationalizationManager.Instance.GetTranslation("registerHotkeyFailed"), hotkeyStr);
+                    string.Format(InternationalizationManager.Instance.GetTranslation("registerHotkeyFailed"),
+                        hotkeyStr);
                 MessageBox.Show(errorMsg);
             }
         }
@@ -627,7 +625,6 @@ private void OnHotkey(object sender, HotkeyEventArgs e)
         {
             if (!ShouldIgnoreHotkeys())
             {
-
                 if (_settings.LastQueryMode == LastQueryMode.Empty)
                 {
                     ChangeQueryText(string.Empty);