Added: The ability to set the number of threads (NOT SUPPORTED!) to use for tasks using THREAD_LIMIT environment variable.

src/NzbDrone.Core/Messaging/Commands/CommandExecutor.cs

@@ -17,7 +17,9 @@ namespace NzbDrone.Core.Messaging.Commands
         private readonly IEventAggregator _eventAggregator;
 
         private static CancellationTokenSource _cancellationTokenSource;
-        private const int THREAD_LIMIT = 3;
+        private const int THREAD_UPPER_BOUND = 10;
+        private const int THREAD_LOWER_BOUND = 2;
+        private const int THREAD_LIMIT = 2;
 
         public CommandExecutor(IServiceFactory serviceFactory,
                                IManageCommandQueue commandQueueManager,
@@ -117,7 +119,16 @@ namespace NzbDrone.Core.Messaging.Commands
         {
             _cancellationTokenSource = new CancellationTokenSource();
 
-            for (int i = 0; i < THREAD_LIMIT; i++)
+            var envLimit = Environment.GetEnvironmentVariable("THREAD_LIMIT") ?? $"{THREAD_LIMIT}";
+            int threadLimit = THREAD_LIMIT;
+            if (int.TryParse(envLimit, out int parsedLimit)) threadLimit = parsedLimit;
+
+            threadLimit = Math.Max(THREAD_LOWER_BOUND, threadLimit);
+            threadLimit = Math.Min(THREAD_UPPER_BOUND, threadLimit);
+            
+            _logger.Info("Starting {} threads for tasks.", threadLimit);
+
+            for (int i = 0; i < threadLimit + 1; i++)
             {
                 var thread = new Thread(ExecuteCommands);
                 thread.Start();