Poll() is causing deadlock

[duduita]

Describe the bug
When making serial HTTP requests using a static HTTP client, it's causing deadlocks, given a timing issue on poll(), which is used internally by the OS when making static HTTP clients.

To Reproduce
Run the following app on WiFi:

using Meadow;
using Meadow.Devices;
using System;
using System.Net.Http;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using Timer = System.Timers.Timer;
using System.Diagnostics;

using System.Net;
using System.Net.Sockets;

namespace MeadowApp
{
    // Change F7FeatherV2 to F7FeatherV1 for V1.x boards
    public class MeadowApp : App<F7FeatherV2>
    {
        private static HttpClient _httpClient = new HttpClient();
        private static Stopwatch sw = new Stopwatch();

        public override async Task Run()
        {
            int count = 0;

            _httpClient.BaseAddress = new Uri("https://postman-echo.com");
            
            Device.NetworkAdapters.NetworkConnected += async (sender, args) =>
            {
                Console.WriteLine("network connected");
                while (true)
                {
                    await DoStaticHttpRequest(count++);
                }
            };

            return;
        }


        async Task DoStaticHttpRequest(int instance)
        {
            Console.WriteLine($"start {instance}");
            string payload =
                    "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";

            sw.Start();

            var content = new StringContent(payload, Encoding.UTF8);
            var result = await _httpClient.PostAsync("https://postman-echo.com/post", content);

            sw.Stop();
            Console.WriteLine($"end {instance}, success:{result.IsSuccessStatusCode}, elapsed: {sw.Elapsed.ToString()}");
            sw.Reset();
            
        }
    }
}

Expected behavior
It should not cause a deadlock.

Meadow (please complete the following information as best as you can):
Model: F7Micro
Hardware version: F7CoreComputeV2
Device name: MeadowCoreCompute

Hardware Information
Processor type: STM32F777IIK6
ID: 3A-00-21-00-0D-50-4B-55-30-38-31-20
Serial number: 20523874554B
Coprocessor type: ESP32
MAC Address -
WiFi: 4C:75:25:D5:78:A0

Firmware Versions
OS: 1.11.0.2
Mono: 1.11.0.2
Coprocessor: 1.11.0.0
Protocol: 7

Additional context

• It's only happening on WiFI, on native networks (cell and ethernet) it's working fine.
• The problem seems to be on poll teardown/poll interrupt handler, since before deadlocking, it was the last logs I could see.
• This seems to be a timing issue, since when I enable USE_MEADOW_DEBUG_HELPERS or just add a few syslogs on espcp_usrsock_sockif, just to find in which part of the code we are getting stuck, the deadlocks don't happen. But, when I disable the UART trace meadow uart trace disable, then I can see them. So, it sounds to me like a timing issue indeed, since the few milliseconds the logs consume might add a delay between each poll request, consequently, somehow reducing the chance of having a deadlock.
• This workaround seems working for now, it might give us a clue about the problem.