CODEWITHSUNDEEP
.netstate-machine
wonderful world
wonderful world

Reputation: 11599

What is the use of StateMachineAttribute in .NET?

I came across a class called StateMachineAttribute in the documentation. What is the purpose of StateMachine in .NET and what StateMachineAttribute is used for?

Upvotes: 0

Views: 858

Answers (1)

Dmitry Kolchev
Dmitry Kolchev

Reputation: 2216

When you implement async method, C# compiler generate method with AsyncStateMachineAttribute that is derived from StateMachineAttribute

C# code

...
public async Task HelloWorldAsync()
{
        await Console.Out.WriteLineAsync("Hello World!");
}
...

"Real" method (generated by compiler)

[AsyncStateMachine(typeof(<HelloWorldAsync>d__4))]
[DebuggerStepThrough]
public Task HelloWorldAsync()
{
    <HelloWorldAsync>d__4 stateMachine = new <HelloWorldAsync>d__4();
    stateMachine.<>4__this = this;
    stateMachine.<>t__builder = AsyncTaskMethodBuilder.Create();
    stateMachine.<>1__state = -1;
    AsyncTaskMethodBuilder <>t__builder = stateMachine.<>t__builder;
    <>t__builder.Start(ref stateMachine);
    return stateMachine.<>t__builder.Task;
}

Really StateMachineAttribute isn't used by compiler. For methods that are state machine methods, the compiler will apply the AsyncStateMachineAttribute or IteratorStateMachineAttribute

Upvotes: 1

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