How to create an IAsyncResult that immediately completes?

问题

I am implementing an interface which requires implementations of BeginDoSomething and EndDoSomething methods. However my DoSomething isn't really long-running. For simplicity assume DoSomething only compares two variables and return whether a > b

So my BeginDoSomething should be like:

protected override IAsyncResult BeginDoSomething(int a, int b, AsyncCallback callback, object state)
{
     bool returnValue = a > b;
     return ...; //what should I return here?  
     //The method actually already completed and I don't need to wait for anything
 }

I don't know what I should return. I only implement BeginDoSomething because I have to, not because my method is long-running. Do I need to implement my own IAsyncResult? Is there an implementation already in .NET libraries?

回答1:

The quick hack way of doing it is to use a delegate:

protected override IAsyncResult BeginDoSomething(int a, int b, AsyncCallback callback, object state)
{
     bool returnValue = a > b;
     Func<int,int,bool> func = (x,y) => x > y;
     return func.BeginInvoke(a,b,callback,state);
}

The downside of this approach, is that you need to be careful if two threads will be calling this method concurrently you'll get an error.

回答2:

This is a little quick and dirty, but you can implement a class that implements IAsyncResult like so:

    public class MyAsyncResult : IAsyncResult
    {
        bool _result;

        public MyAsyncResult(bool result)
        {
            _result = result;
        }

        public bool IsCompleted
        {
            get { return true; }
        }

        public WaitHandle AsyncWaitHandle
        {
            get { throw new NotImplementedException(); }
        }

        public object AsyncState
        {
            get { return _result; }
        }

        public bool CompletedSynchronously
        {
            get { return true; }
        }
    }

Then use it in your BeginDoSomething like this:

    return new MyAsyncResult(a > b);

来源：https://stackoverflow.com/questions/5037422/how-to-create-an-iasyncresult-that-immediately-completes

标签

.net

asynchronous

delegates

iasyncresult