using System;   

using System.Collections;

using System.Threading.Tasks;

public class Program

{

    public static void Main()

    {

         ArrayList forecasts = new ArrayList();

         for(var k = 0; k < 100; k++){

             forecasts.Add(k);

         }

        int size = 6;

        var taskNum = (int) Math.Ceiling(forecasts.Count / (double) size);

        Console.WriteLine("task number:" + taskNum);

        Console.WriteLine("item number:" + forecasts.Count);

        Task[] tasks = new Task[taskNum];

        var i = 0;

        for(i = 0; i < taskNum; i++) {

            int start = i * size;

            if (forecasts.Count - start < size) {

                size = forecasts.Count - start;

            }

            // Method 1: This works well, but need take some time to finish

            //tasks[i] = new Task(() => {

                //var batchedforecastRows = forecasts.GetRange(start, size);

                // GbqTable.InsertRowsAsync(batchedforecastRows);

                //Console.WriteLine("batchID:" + (i + 1) + "["+string.Join( ",", batchedforecastRows.ToArray())+"]"); 

            //});

            // tasks[i].RunSynchronously();

            // Method 2: will lose data: (94, 95) and batchId is messed

            // Sample Print below: 

            // batchID:18 Inserted:[90,91,92,93]

            // batchID:18 Inserted:[96,97,98,99]

            tasks[i] = Task.Run(() => {

                var batchedforecastRows = forecasts.GetRange(start, size);

                // GbqTable.InsertRowsAsync(batchedforecastRows);

                Console.WriteLine("batchID:" + (i + 1) + " Inserted:["+string.Join( ",", batchedforecastRows.ToArray())+"]"); 

            });

        }

    }

}