What’s the meaning of “UseTaskFriendlySynchronizationContext”?

There is a new app setting in asp.net 4.5

<add key="aspnet:UseTaskFriendlySynchronizationContext" value="true" />

code like this can run in asp.net 4.0
protected void Button1_Click(object sender, EventArgs e)
{
    CallAysnc();
}

public void CallAysnc()
{
    AsyncOperation asyncOp = AsyncOperationManager.CreateOperation(Guid.NewGuid().ToString());

    WebClient client = new WebClient();
    client.DownloadStringCompleted += (object sender, DownloadStringCompletedEventArgs e) =>
    {
        asyncOp.PostOperationCompleted(CallCompleted, e.Result);
    };
    client.DownloadStringAsync(new Uri("http://www.google.com"));
}

private void CallCompleted(object args)
{
    Response.Write(args.ToString());
}

But it doesn’t work in asp.net 4.5,and when I remove the new appsetting,it works again!

So what’s the meaning of “UseTaskFriendlySynchronizationContext” ?

Answers:

Thank you for visiting the Q&A section on Magenaut. Please note that all the answers may not help you solve the issue immediately. So please treat them as advisements. If you found the post helpful (or not), leave a comment & I’ll get back to you as soon as possible.

Method 1

Regarding UseTaskFriendlySynchronizationContext, from Microsoft Forums:

That tells ASP.NET to use an entirely new asynchronous pipeline which
follows CLR conventions for kicking off asynchronous operations,
including returning threads to the ThreadPool when necessary. ASP.NET
4.0 and below followed its own conventions which went against CLR guidelines, and if the switch is not enabled it is
very easy for asynchronous methods to run synchronously, deadlock the request, or otherwise not behave as expected.

Also, I think AsyncOperationManager is intended for desktop applications. For ASP.NET apps you should be using RegisterAsyncTask and setting <%@ Page Async="true", see here for more details.

So using the new c# keywords your example would be:

protected void Button1_Click(object sender, EventArgs e)
{
    RegisterAsyncTask(new PageAsyncTask(CallAysnc));
}

private async Task CallAysnc()
{
    var res = await new WebClient().DownloadStringTaskAsync("http://www.google.com");
    Response.Write(res);
}

The aim is to support the following by release but is not currently supported in the beta:
protected async void Button1_Click(object sender, EventArgs e)
{
    var res = await new WebClient().DownloadStringTaskAsync("http://www.google.com");
    Response.Write(res);
}

Method 2

More details, quoted from ASP.NET 4.5.1 documentation for appSettings on MSDN:

aspnet:UseTaskFriendlySynchronizationContext

Specifies how asynchronous code paths in ASP.NET 4.5 behave.

If this key value is set to false [default], asynchronous code paths in ASP.NET 4.5 behave as they did in ASP.NET 4.0. If this key
value is set to true, ASP.NET 4.5 uses code paths that are optimized
for Task-returning APIs. Setting this compatibility switch is
mandatory for WebSockets-enabled applications, for using Task-based
asynchrony in Web Forms pages, and for certain other asynchronous
behaviors.


All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

0 0 votes
Article Rating
Subscribe
Notify of
guest

0 Comments
Inline Feedbacks
View all comments
0
Would love your thoughts, please comment.x
()
x