PipeReader CancelPendingRead not cancelling current read operation

Question

I expected to be able to start another read operation if I cancel the current read with CancelPendingRead. But this code throws a InvalidOperationException. Does CancelPendingRead not work as i think or what could be the problem? I'm testing with .Net Core 3.1.

try
{
    var p = new Pipe();
    await p.Writer.WriteAsync( new Byte[] { 1, 2, 3 } );

    var rr = await p.Reader.ReadAsync();
    p.Reader.CancelPendingRead();

    rr = await p.Reader.ReadAsync(); // Reading is already in progress.
}
catch ( InvalidOperationException ex )
{
    Console.WriteLine( ex );
}

Answer 1

Ok I found the problem: CancelPendingRead does cancel a waiting read. It does NOT not "cancel" a already executed read. The solution is to advance the reader to the start of the just read buffer.

var p = new Pipe();
var readTask = p.Reader.ReadAsync();

p.Reader.CancelPendingRead();

var rr = await readTask;
// rr.IsCanceled; => is true
p.Reader.AdvanceTo( rr.Buffer.Start );
rr = await p.Reader.ReadAsync();