Revert "Switch to Parallel.ForEach for list processing with MaxParallelism"

This reverts commit ebb2b4eca3.

src/NzbDrone.Core/ImportLists/FetchAndParseImportListService.cs

@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
 using NLog;
+using NzbDrone.Common.TPL;
 using NzbDrone.Core.Parser.Model;
 
 namespace NzbDrone.Core.ImportLists
@@ -40,7 +41,10 @@ namespace NzbDrone.Core.ImportLists
 
             _logger.Debug("Available import lists {0}", importLists.Count);
 
-            Parallel.ForEach(importLists, new ParallelOptions { MaxDegreeOfParallelism = 5 }, importList =>
+            var taskList = new List<Task>();
+            var taskFactory = new TaskFactory(TaskCreationOptions.LongRunning, TaskContinuationOptions.None);
+
+            foreach (var importList in importLists)
             {
                 var importListLocal = importList;
                 var importListStatus = _importListStatusService.GetLastSyncListInfo(importListLocal.Definition.Id);
@@ -52,10 +56,12 @@ namespace NzbDrone.Core.ImportLists
                     if (DateTime.UtcNow < importListNextSync)
                     {
                         _logger.Trace("Skipping refresh of Import List {0} ({1}) due to minimum refresh interval. Next sync after {2}", importList.Name, importListLocal.Definition.Name, importListNextSync);
-                        return;
+                        continue;
                     }
                 }
 
+                var task = taskFactory.StartNew(() =>
+                     {
                          try
                          {
                              var importListReports = importListLocal.Fetch();
@@ -73,7 +79,12 @@ namespace NzbDrone.Core.ImportLists
                          {
                              _logger.Error(e, "Error during Import List Sync of {0} ({1})", importList.Name, importListLocal.Definition.Name);
                          }
-            });
+                     }).LogExceptions();
+
+                taskList.Add(task);
+            }
+
+            Task.WaitAll(taskList.ToArray());
 
             result = result.DistinctBy(r => new { r.Author, r.Book }).ToList();
 
@@ -94,8 +105,13 @@ namespace NzbDrone.Core.ImportLists
                 return result;
             }
 
+            var taskList = new List<Task>();
+            var taskFactory = new TaskFactory(TaskCreationOptions.LongRunning, TaskContinuationOptions.None);
+
             var importListLocal = importList;
 
+            var task = taskFactory.StartNew(() =>
+            {
                 try
                 {
                     var importListReports = importListLocal.Fetch();
@@ -113,6 +129,11 @@ namespace NzbDrone.Core.ImportLists
                 {
                     _logger.Error(e, "Error during Import List Sync of {0} ({1})", importList.Name, importListLocal.Definition.Name);
                 }
+            }).LogExceptions();
+
+            taskList.Add(task);
+
+            Task.WaitAll(taskList.ToArray());
 
             result = result.DistinctBy(r => new { r.Author, r.Book }).ToList();