Run Process on special thread and await result

Question

I had this simple code...

var map = new ReferencedEntityMapAce(uow); ... which worked fine

but now I need to run it on a different thread (with a large stack size due to its recursion) and await its result before continuing.

What is the simplest way of doing this? (I can't see a way of giving Task a specific thread or telling it to create one with a large stack)

Background (if needed): The code above that I had been using for months suddenly starting throwing a stack overflow exception. I believe I have just hit a limit since it is now processing nearly 140k entities with relationships to decide what order they should be saved to initialize a new database. I cannot alter the recursion part - that is in an external third-party library I use with no plans to update it.

I have hacked up test code to prove that it does indeed work when procesed on a large stack thread.

Answer 1

You can use Thread class with the maxStackSize constructor but if you want to keep Task semantic you have to implement custom TaskScheduler like as follows:

public class BigStackTaskScheduler : TaskScheduler
{
    private int _stackSize;

    public BigStackTaskScheduler(int stackSize)
    {
        _stackSize = stackSize;
    }

    // we don't need to keep a tasks queue here
    protected override IEnumerable<Task> GetScheduledTasks()
    {
        return new Task [] { };
    }

    protected override void QueueTask(Task task)
    {
        var thread = new Thread(ThreadWork, _stackSize);
        thread.Start(task);
    }

    // we aren't going to inline the execution
    protected override bool TryExecuteTaskInline(Task task, bool taskWasPreviouslyQueued)
    {
        QueueTask(task);
        return false;
    }

    private void ThreadWork(object obj)
    {
        if (obj is Task task)
            TryExecuteTask(task);
    }
}

class Program
{
    async static Task Test()
    {
        var taskFactory = new TaskFactory(
            CancellationToken.None, TaskCreationOptions.DenyChildAttach,
            TaskContinuationOptions.None, new BigStackTaskScheduler(0xffff * 2));
        await taskFactory.StartNew(() => { Console.WriteLine("Task"); });
    }

    static void Main(string[] args)
    {
        Test().Wait();
    }
}

Update: As possible alternative of custom TaskScheduler the TaskCompletionSource can be used:

class Program
{
    static Task<TOut> ThreadWithCustomStack<TIn, TOut>(Func<TIn, TOut> action, TIn arg, int stackSize)
    {
        var tcs = new TaskCompletionSource<TOut>();

        var thread = new Thread(new ThreadStart(() => 
        {
            try
            {
                tcs.SetResult(action(arg));
            }
            catch (Exception e)
            {
                tcs.SetException(e);
            }
        }), stackSize);

        thread.Start();
        thread.Join();

        return tcs.Task;
    }

    async static Task Test()
    {
        var result = await ThreadWithCustomStack(
            arg => { Console.WriteLine("Task"); return arg.ToString(); }, 
            2, 
            0xffff * 2);
    }

    static void Main(string[] args)
    {
        Test().Wait();
    }
}