using System;

using System.Threading.Tasks;

​

public class Runner

{

    bool _isRunning = false;

    private object _lock = new object ();

    bool _reRunTriggered = false;

    public async Task EnsureRunThingsAsync(bool overrideRunLock = false)

    {

        // ensure RunTasksAsync can never run more than once at the same time

        // but also ensure it will run again when its being called while its being run

        if (!EnterLocked(overrideRunLock))

            return;

        // do some things that should only happen one time at a time

        await Task.Delay(1000);

        if (_reRunTriggered)

        {

            Console.WriteLine("run again because rerun requested");

            await EnsureRunThingsAsync(true);

        }

​

        _isRunning = false;

    }

​

    private bool EnterLocked(bool overrideRunLock)

    {

        lock (_lock)

        {

            if (_isRunning && !overrideRunLock)

            {

                _reRunTriggered = true;

                Console.WriteLine("locked > early exit, request rerun");

                return false;

            }

​

            Console.WriteLine("run function");

            _reRunTriggered = false;

            _isRunning = true;

        }

​

        return true;

    }

}

​

public class Program

{

    public static async Task Main()

    {

        var r = new Runner();

        var t1 = r.EnsureRunThingsAsync();

        var t2 = r.EnsureRunThingsAsync();

        await Task.WhenAll(t1, t2);

    }

}