WWW blocks main thread

Unity Engine
1

I try to download simple test data asynchronously:

using System.Collections;
using UnityEngine;

public class Download : MonoBehaviour
{
    public string _url = "http://ipv4.download.thinkbroadband.com/10MB.zip";

    WWW _www;

    public void Start()
    {

    }

    public void Update()
    {
        if (Input.GetMouseButtonDown(0))
        {
            StartCoroutine(DownloadAsync(_url));
        }

        if (_www == null)
        {
            return;
        }

        if (_www.isDone)
        {
            return;
        }

        Debug.Log("Update(" + _url + "), www.progress: " + _www.progress + ",  www.bytesDownloaded: " + _www.bytesDownloaded);
    }

    public IEnumerator DownloadAsync(string url)
    {
        Debug.Log("DownloadAsync(" + url + ")");

        _www = new WWW(url);

        yield return _www;

        Debug.Log("DownloadAsync(" + url + ") finished");
    }
}

When clicking the mouse button, the entire game stops. I tested it in Unity Editor, Windows and Android.

Just what am I doing wrong?

2

Hmmm… it seems that as soon as I try to access properties of the _www instance in Update(), it blocks the main thread.

EDIT

The main thread is blocked when I access the _www.bytesDownloaded property! That’s a bummer. That way that property is completely useless. I can always go www.bytes.Length at the end. What I want to know is how many bytes have been downloaded SO FAR as progress indication.