Re: Async File IO is not async?

Hi Alex,

I have altered your example into this [2]
because the kb had this line [1] which made me wonder ;)

// Ryan

[1]

Extending a File
Another reason that I/O operations are completed synchronously is the
operations themselves. On Windows NT, any write operation to a file
that extends its length will be synchronous.

[2]

using System; System;
using System.IO; System.IO;
using System.Threading; System.Threading;

namespace AsyncIOTest AsyncIOTest
{
  class Program
  {
    static void Main()
    {
      using (FileStream file = File.Create("out.test", 0x1000,
FileOptions.Asynchronous))
      {
        file.Position = 512 * 1024 * 1024 - 1;
        file.WriteByte(0);
      }

      using (FileStream file = File.Open("out.test",FileMode.Open,
FileAccess.Write))
     {
        ManualResetEvent evt = new ManualResetEvent(false);

        Byte[] buffer = new Byte[512 * 1024 * 1024];
        file.BeginWrite(buffer, 0, buffer.Length, Program.OnWriteComplete, evt);

        evt.WaitOne();
      }

      File.Delete("out.test");
    }

    static void OnWriteComplete(IAsyncResult ar)
    {
      ManualResetEvent evt = (ManualResetEvent)ar.AsyncState;

      evt.Set();
    }
  }
}

On Jan 18, 2008 6:08 AM, Peter Ritchie
<[email protected]> wrote:
>
> On Thu, 17 Jan 2008 22:09:27 -0600, Alex Ivanoff
> <[email protected]> wrote:
>
> >A quick examination with Reflector reveals that BeginWrite and BeginRead
> do not satisfy most (if not all) of the requirements of a "true" async IO
> outlined here: http://support.microsoft.com/kb/156932.
> >
>
> Did you reflect on FileStream.BeginWriteCore?
>
>
>
>
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