Uploading async to Azure Blob Storage never returns
The error is almost certainly further up your call stack, where some method is blocking on the returned task (e.g., Task<T>.Result, Task.Wait, etc.). This will deadlock if the thread being blocked is required for the task to complete.
I explain this situation in full on my blog, but the gist of it is this:
awaitby default will capture a "context" and use that to resume theasyncmethod.- If this code is executed in an ASP.NET request context, this "context" is an ASP.NET
SynchronizationContext; if this code is executed in a UI thread, this "context" is a UISynchronizationContext. - Both the ASP.NET
SynchronizationContextand UISynchronizationContextonly allow one thread in them at a time.
Thus, when the calling code blocks on the returned Task, it is holding a thread within that context, preventing the Task from completing.