PInvoke 호출을 이용한 비동기 파일 작업

그냥 잠깐 만들어 보았는데 기록을 남기는 차원에서 써봅니다. ^^

닷넷은 비동기 메서드 호출이 잘 되어 있지만, 가끔은 PInvoke로 직접 해야 하는 경우도 있을 듯 싶어 예제 코드 삼아 만들어 보았습니다.

using Microsoft.Win32.SafeHandles;
using System;
using System.Diagnostics;
using System.IO;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading;

class Program
{
    [DllImport("kernel32.dll", SetLastError = true)]
    public static extern SafeFileHandle CreateFile(
       String pipeName,
       uint dwDesiredAccess,
       uint dwShareMode,
       IntPtr lpSecurityAttributes,
       uint dwCreationDisposition,
       uint dwFlagsAndAttributes,
       IntPtr hTemplate);

    [DllImport("kernel32.dll", SetLastError = true)]
    static extern bool WriteFile(SafeFileHandle hFile, byte[] lpBuffer,
       int nNumberOfBytesToWrite, out uint lpNumberOfBytesWritten,
       [In] ref System.Threading.NativeOverlapped lpOverlapped);

    public const int FILE_FLAG_OVERLAPPED = 0x40000000;

    static void Main(string[] args)
    {
        EventWaitHandle exitEvent = new EventWaitHandle(false, EventResetMode.ManualReset);
        string txt = new string('t', 1024 * 1024 * 600);
        byte[] buf = Encoding.ASCII.GetBytes(txt);

        while (true)
        {
            File.Delete(@"C:\temp\test.txt");
            using (SafeFileHandle pHandle = CreateFile(@"c:\temp\test.txt",
                  (uint)FileAccess.ReadWrite,
                  0,
                  IntPtr.Zero,
                  (uint)2,
                  FILE_FLAG_OVERLAPPED,
                  IntPtr.Zero))
            {
                uint written;
                NativeOverlapped o = new NativeOverlapped();

                using (ManualResetEvent writeEvent = new ManualResetEvent(false))
                {
                    o.EventHandle = writeEvent.SafeWaitHandle.DangerousGetHandle();

                    Stopwatch st = new Stopwatch();
                    st.Start();
                    if (WriteFile(pHandle, buf, buf.Length, out written, ref o) == false)
                    {
                        int lastError = Marshal.GetLastWin32Error();
                        if (lastError == 997) //  ERROR_IO_PENDING == 997
                        {
                            Console.WriteLine("async");
                        }
                        else
                        {
                            // Write File Error
                            Console.WriteLine("Write File Error");
                            break;
                        }

                        WaitHandle[] waitHandles = new WaitHandle[] { writeEvent, exitEvent };
                        int completeCode = WaitHandle.WaitAny(waitHandles, Timeout.Infinite, false);
                        if (completeCode == 1) // exitEvent signaled
                        {
                            break;
                        }
                    }

                    st.Stop();
                    Console.WriteLine(st.ElapsedMilliseconds);
                }

                Thread.Sleep(1000);
            }
        }
    }
}

Synchronous and Asynchronous I/O
; https://docs.microsoft.com/en-us/windows/win32/fileio/synchronous-and-asynchronous-i-o

Asynchronous Disk I/O Appears as Synchronous on Windows NT, Windows 2000, and Windows XP
; http://support.microsoft.com/kb/156932