Using TPL how do I set a max threadpool size

Question

I am using the TPL to add new tasks to the system thread pool using the function Task.Factory.StartNew(). The only problem is that I am adding a lot of threads and I think it is creating too many for my processor to handle. Is there a way to set a maximum number of threads in this thread pool?

Answer 1

Typically TPL determines a good "default" threadpool size. If you really need fewer threads, see How to: Create a Task Scheduler That Limits the Degree of Concurrency

Answer 2

The default TaskScheduler (obtained from TaskScheduler.Default) is of type (internal class) ThreadPoolTaskScheduler. This implementation uses the ThreadPool class to queue tasks (if the Task isn't created with TaskCreationOptions.LongRunning - in this case a new thread is created for each task).

So, if you want to limit the # of threads available to Task objects created via new Task(() => Console.WriteLine("In task")), you can limit the available threads in the global threadpool like this:

// Limit threadpool size
int workerThreads, completionPortThreads;
ThreadPool.GetMaxThreads(out workerThreads, out completionPortThreads);
workerThreads = 32;
ThreadPool.SetMaxThreads(workerThreads, completionPortThreads);

The call to ThreadPool.GetMaxThreads() is done to avoid shrinking the completionPortThreads.

Note that this may be a bad idea - since all Tasks without a specified scheduler, and any number of other classes use the default ThreadPool, setting the size too low could cause side-effects: Starvation, etc.