Overview
Asynchronous Programming Model (APM): C# 1.0 / .NET 1.0 Style
Legacy model using the IAsyncResult pattern.
Asynchronous calls are made using Begin and End methods on an API, with callbacks and state being passed between them.
public class MyClass
{
public IAsyncResult BeginRead( byte [] buffer, int offset, int count, AsyncCallback callback, object state);
public int EndRead(IAsyncResult asyncResult);
}
Exception handling
Exceptions can be thrown from BeginRead (such as trying to read from a stream that has already been closed). Unexpected errors occurring during the async request (e.g. I/O error when reading a file), occur on the thread pool thread and will throw an exception when calling EndRead.
Event-based Asynchronous Pattern (EAP): C#2.0 / .NET 2.0 Style
public class MyClass
{
public void ReadAsync(byte [] buffer, int offset, int count);
public event ReadCompletedEventHandler ReadCompleted;
}
Task-based Asynchronous Pattern (TAP): .NET 4.0 onwards
The modern recommended asynchronous programming model, wrapping asynchronous operations in a single approach, and adding first-class async keywords async and await to the language.
public class MyClass
{
public Task<int> ReadAsync(byte [] buffer, int offset, int count);
}