Proper use of ParallelOptions, TaskCreationOptions and Task.Factory.StartNew?

Question

Please suggest which method is proper(if any) for correct and efficient use of ParallelOptions, TaskCreationOptions and Task.Factory.StartNew(() =>.

private void NeedToUse_MaxDegreeOfParallelism_Method1() { CancellationTokenSource tokenFor_task = new CancellationTokenSource(); ParallelOptions parOpts = new ParallelOptions(); //parOpts.CancellationToken = tokenFor_task_tpl_Pair01.Token; parOpts.MaxDegreeOfParallelism = Environment.ProcessorCount; //parOpts.TaskScheduler = TaskScheduler.Default; TaskCreationOptions tco = new TaskCreationOptions(); tco = TaskCreationOptions.PreferFairness; Task task = null; task = Task.Factory.StartNew(() => { while (!tokenFor_task.IsCancellationRequested) { LongRunningMethod(); } }, tokenFor_task.Token, tco, TaskScheduler.Default); } private void NeedToUse_MaxDegreeOfParallelism_Method2() { //CancellationTokenSource tokenFor_task = new CancellationTokenSource(); ParallelOptions parOpts = new ParallelOptions(); parOpts.CancellationToken = tokenFor_task_tpl_Pair01.Token; parOpts.MaxDegreeOfParallelism = Environment.ProcessorCount; parOpts.TaskScheduler = TaskScheduler.Default; TaskCreationOptions tco = new TaskCreationOptions(); tco = TaskCreationOptions.PreferFairness; Task task = null; task = Task.Factory.StartNew(() => { while (!parOpts.CancellationToken.IsCancellationRequested) { LongRunningMethod(); } }, parOpts.CancellationToken, tco, parOpts.TaskScheduler); } private void NeedToUse_MaxDegreeOfParallelism_Method3() { CancellationTokenSource tokenFor_task = new CancellationTokenSource(); ParallelOptions parOpts = new ParallelOptions(); //parOpts.CancellationToken = tokenFor_task_tpl_Pair01.Token; parOpts.MaxDegreeOfParallelism = Environment.ProcessorCount; //parOpts.TaskScheduler = TaskScheduler.Default; TaskCreationOptions tco = new TaskCreationOptions(); tco = TaskCreationOptions.PreferFairness; Task task = null; task = Task.Factory.StartNew(() => { Parallel.Invoke(parOpts, () => //while is already in LongRunningMethod() because can not be here //while (!tokenFor_task.IsCancellationRequested) //{ LongRunningMethod() //} ); }, tokenFor_task.Token, tco, TaskScheduler.Default); } private void NeedToUse_MaxDegreeOfParallelism_Method4() { CancellationTokenSource tokenFor_task = new CancellationTokenSource(); ParallelOptions parOpts = new ParallelOptions(); //parOpts.CancellationToken = tokenFor_task_tpl_Pair01.Token; parOpts.MaxDegreeOfParallelism = Environment.ProcessorCount; //parOpts.TaskScheduler = TaskScheduler.Default; TaskCreationOptions tco = new TaskCreationOptions(); tco = TaskCreationOptions.PreferFairness; Task task = null; Parallel.Invoke(parOpts, () => task = Task.Factory.StartNew(() => { while (!tokenFor_task.IsCancellationRequested) { LongRunningMethod(); } }, tokenFor_task.Token, tco, TaskScheduler.Default) ); }

Currently I don't get any errors. First and second methods do not take into account MaxDegreeOfParallelism which I need to use. Ideally I would not use Parallel.Invoke but how to include parOpts.MaxDegreeOfParallelism in Task.Factory.StartNew?

svick · Accepted Answer · 2013-07-26 12:58:51Z

Your code and question don't make much sense. Task.Factory.StartNew() doesn't accept MaxDegreeOfParallelism, because it executes a single action. Parallel.Invoke() does accept that parameter, but it doesn't make any sense to use that method when you have a single action.

Instead of asking a very specific question like this, I think you should step back, look at what you're actually trying to achieve and then possibly ask a new question about that.

EDIT: Now I think I finally understand what you're trying to do: on each core, you want to execute a separate loop. To do that, you could for example use Parallel.For():

Parallel.For(0, Environment.ProcessorCount, parOpts, () => { while (!tokenFor_task.IsCancellationRequested) { LongRunningMethod(); } });

I need LongRunningMethod() to be executed parallelly on all cores when possible.

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