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CSharp · Console

/Program.cs

using System;
using System.Collections.Generic;
using System.Threading.Tasks;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Diagnostics;

public class Program
{
	public static async Task Main()
	{
		FillList();
		
		var stopWatch1 = Stopwatch.StartNew();
		var results1 = await QueryApiAsParallel();
		stopWatch1.Stop();
		
		var stopWatch2 = Stopwatch.StartNew();
		var results2 = await QueryApiAsParallelOptimized();
		stopWatch2.Stop();
		
		Console.WriteLine($"Query1: {stopWatch1.ElapsedMilliseconds} ms ({results1.Select(s => int.Parse(s)).Sum()})");
		Console.WriteLine(string.Join(',', results1));
		Console.WriteLine("");
		Console.WriteLine($"Query2: {stopWatch2.ElapsedMilliseconds} ms ({results2.Select(s => int.Parse(s)).Sum()})");
		Console.WriteLine(string.Join(',', results2));
	}
	
	public static async Task<string[]> QueryApiAsParallelOptimized() {
		int maximum = 10000; 
		int rangeSize = 1000;

		var results = new ConcurrentBag<string[]>();
		var partitions = Enumerable.Range(0, maximum);
		var chunks = partitions.Chunk(rangeSize);
		
		var parallelOptions = new ParallelOptions()
		{
			MaxDegreeOfParallelism = 1000
		};
		
		await Parallel.ForEachAsync(chunks, parallelOptions, async (range, token) =>
		{
			int skip = range.First();
			string[] names = await CallApiAsync(skip, rangeSize);
			results.Add(names);
		});
		
		string[] flattened = results.SelectMany(x => x).ToArray();

		return flattened;
	}
	
	public static async Task<string[]> QueryApiAsParallel() {
		int maximum = 10000; // I don't want to query more than 10000 results even I know that are a lot more results
		int rangeSize = 1000; // maximum number that can be received via API

		Task<string[]>[] tasks = Partitioner.Create(0, maximum, rangeSize).AsParallel().Select(async (range, index) => 
		{
			int skip = range.Item1;
			string[] names = await CallApiAsync(skip, rangeSize);

			return names;
		}).ToArray();

		string[][] tasksCompleted = await Task.WhenAll(tasks);

		string[] flattened = tasksCompleted.SelectMany(x => x).ToArray();

		return flattened;
	}
	
	private static async Task<string[]> CallApiAsync(int skip, int take) 
	{
		await Task.Delay(100);
		return _list.Skip(skip).Take(take).ToArray();
	}
	
	private static List<string> _list = new List<string>();
	private static Random _rnd = new Random();
	private static void FillList(){
		for(var i = 0; i< 100000; i++){
			_list.Add($"{_rnd.Next(100,200)}");
		}
	}
}