MVC Application hanging when using Tasks.WhenAll with Entity Framework SaveChangesAsync

Question

I've been learning how to use asynchronous calls with Entity Framework recently and have been experimenting with the behaviors of the various calls. However, I've come up against a problem and I'm not sure what's causing it.

So in my data access class, I have an async method like this:

public static async Task update(int id)
{
    var task1 = doSomething(id);
    var task2 = doSomethingElse(id);
    await Task.WhenAll(task1, task2);    
}

It calls on the two async tasks which are in the following form:

private static async Task doSomething(int id)
{
    using (var context = new dbEntity())
    {
        //...make changes to the context
        await context.SaveChangesAsync();
    }
}

private static async Task doSomethingElse(int id)
{
    using (var context = new dbEntity())
    {
        //...make changes to the context
        await context.SaveChangesAsync();
    }
}

Finally, in the controller, I'm calling on the data access async task like this:

public ActionResult Index(int id)
{
    var task = DataAccess.update(id);
    task.Wait();
    return View();
}

When I go and trigger the Index action, my application just hangs indefinitely. What's strange is that when I stop the application and look at my database, it appears that both of the async SaveChanges went through and the data in my database has been modified. When I remove the call to task.Wait(), the application proceeds as normal. I think I'm causing a deadlock somewhere, but I don't know where. Can some please point me in the right direction and tell me what exactly is happening here?

Thanks!

You should be using an async controller method also eg. asp.net/mvc/overview/performance/… — timothyclifford
– timothyclifford, Commented Jun 9, 2016 at 6:18

halfer · Accepted Answer · 2019-02-16 19:14:49Z

2

You can not mix async code with synchronous code. When you use task.wait() you are blocking the thread.

Please change the controller action to the following:

public async Task<ActionResult> Index(int id)
{
    await DataAccess.update(id);
    return View();
}

edited Feb 16, 2019 at 19:14

halfer

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answered Jun 9, 2016 at 6:21

Soma Yarlagadda

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Comments

Jim · Accepted Answer · 2016-06-09 06:20:38Z

1

I am eager to hear why it's stalling, but you should nevertheless change your Index method to asynchronous to complete the pipe...

public async Task<ActionResult> Index(int id)
{
    await DataAccess.update(id);
    return View();
}

answered Jun 9, 2016 at 6:20

Jim

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