Asynchronous Programming in C# 5.0

History has seen different programming models.

• Single Threaded Programming – Involves single execution context
• Multi threaded Programming – Involves multiple execution contexts
• Concurrent/Parallel Programming – Involves multiple simultaneous computations happening across multiple processors
• Synchronous Programming – A thread executes one task at a time until it completes
• Asynchronous Programming – A thread initiates a task, saves the state, continues with another task, and returns back to the original task once the task is complete. Hence tasks are interleaved to each other

C# 5.0 introduces async and await commands to support Asynchronous Programming. In addition .NET 4.5 contains the following APIs that support async programming

• Web Access – HttpClient, SyndicationClient
• Working with files – StorageFile, StreamWriter, StreamReader, XmlReader
• Working with images – MediaCapture, BitmapEncoder, BitmapDecoder
• WCF programming – Synchronous and Asynchronous Operations

A method can be run asynchronous by prefixing with async keyword. Async methods return a Task in TPL.

“await” operator is applied while calling async method to suspend the execution of method until the awaited task completes.

Execution flow in async method

Reference:

https://msdn.microsoft.com/en-us/library/mt674882.aspx