Each await triggers the following code to be abstracted into a new continuation block. The await however, waits for the completion of the async call and then continues as if the code had been called synchronously.īehind the scenes, the async await pattern is essentially a compiler generated Task Continuation State Machine (my term), that uses Task.ContinueWith() to nest multiple await code blocks inside of each other. await Method() īoth methods are called asynchronously - meaning the code executes potentially off the main UI thread so UI (or other background operations on a servers main call context) stay responsive. Calling Async MethodsĪdding the async keyword to a method then allows you to use await to wait on other Task or Task based operations. IOW, the code is executing a continuation of an existing Task operation via await or via Task.ContinueWith(). The key is the Task or Task result value from the method called which allows the called method to participate in the Async call continuation sequence that somewhere up the chain typically gets initiated by a Task.Run() or similar operation. 'Proper' async method definitions tend to be in the form of: public async Task Method() But for classic event handling there's not much of a choice.īefore we look at why that's a problem let's look at 'proper' async/await behavior. In fact, async void is widely panned as a C# anti-pattern, because at its core it doesn't originate from a Task based root operation. Async 101Īsync code can be called in a variety of ways, and the async void handling that is the focus of this post is an exceptional use case that you generally want to avoid in your code. In this post I want to re-iterate one of the most common problems that I have and still continue to run into in Markdown Monster with async code, over 1 year after the async migration:Įvent handlers that use async void or even just plain synchronous void can often hang while processing operations that eventually trigger or fire other overlapping async calls, especially if those operations end up triggering longer running operations that are offloaded on new threads.īefore I jump into dissecting this problem and show my workaround that has worked to 'free up' intermittent hangs, or UI hangs (hanging until you move the mouse etc.) on various occasions, let's do a quick very high level review of how async code work. In the past I've written about pitfalls when using async with WPF specifically a while back in the context of porting a commercial application - Markdown Monster - from mostly sync code to mostly async. But if you're using an older platform like WinForms or WPF, event handling still relies on the older decidedly non-async event delegate processing. The unexpected token void menas that it found the word void when it was not expecting it and since your code has 3 void's it would help in future if you identify the line where Processing thinks it found the error.Async usage in C# is the recommended way to build UI based applications. Use the Auto-format option on the Edit menu to structure your code as it will help you solve the problem.
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