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Async in .NET
Async code allows long-running operations like network and file access to execute without blocking the UI thread. There have been several approaches to async programming in .NET including the Async Programming Model (APM), Event-based Async Pattern (EAP), and Task Parallel Library. The newest approach is to use async and await keywords which allow suspending methods until async operations complete and make control flow easier to reason about.
Async in .NET
- 2. What is Async? Synchronous every line of code is executed in order the next line doesn’t execute until the current one is completed Asynchronous an operation is started, and then code continues A callback is usually executed when the operation completes
- 3. Why Async? Essentialwhen executing long running operations, such as file or network access Especially important when starting operations on the UI thread – async prevents the UI from locking up while the operation completes
- 4. Async Programming Model (APM) .NET’s first crack at async Uses method signatures like Begin* and End* i.e. Stream.BeginRead Returns an “IAsyncResult” object to query status of operation Usually executes a callback when operation is completed
- 5. Event-based Async Pattern (EAP) 2nd attempt at Async Uses events to notify when async operations complete i.e. WebClient.OnDownloadStringCompleted Operation is started with *Async i.e. WebClient.DownloadStringAsync No IAsyncResult – hard to query current status Sometimes they have “OnProgress” events
- 6. Task Async Pattern Uses Task Parallel Library to wrap APM methods Task.Factory.FromAsync(Begin*, End*, args) Get access to Task functionality ContinueWith to execute code after operation is complete ContinueWhenAll to wait for multiple async operations
- 7. The New Hotness– Async & Await In an effort to simplify async even more, Async and Await keywords introduced into .net 4.5 Async – indicates that a method has a point at which it can be suspended Await – suspends the current method until an operation yields a result
- 8. Async Control Flow Starts an async operation by calling async method Execute whatever other code you’d like while operation executes Call await to suspend method until async operation returns This will return control to the previous method in the call stack Once async operation returns, control is restored to method and continues as normal
- 9. Things To Know This is all managed through Tasks Await essentially calls Task.Wait() and automatically returns Task.Result Most of this happens on the same thread Actually uses time slices interleaved within the current thread Meant to be used to create non-blocking operations By convention, async methods should end with “Async”