Asynchronous I/O in C#: Introduction

AsyncMain.cs

static void Main()
{
    var fs = new FileStream("test.txt", FileMode.Open, FileAccess.Read, FileShare.None, 1024, true);
    var buffer = new byte[1024];

    fs.BeginRead(buffer, 0, 1024, ReadCallback, new State { Buffer = buffer, FileStream = fs });

    Console.ReadLine();
}

private static void ReadCallback(IAsyncResult ar)
{
    var state = (State)ar.AsyncState;
    var bytesRead = state.FileStream.EndRead(ar);

    Console.WriteLine(Encoding.UTF8.GetString(state.Buffer, 0, bytesRead));
    state.FileStream.Close();
}

private class State
{
    public FileStream FileStream { get; set; }

    public byte[] Buffer { get; set; }
}

ReadFromFile.cs

static async void ReadFromFile()
{
    using (var fs = new FileStream("test.txt", FileMode.Open, FileAccess.Read))
    {
        var buffer = new byte[1024];
        var bytesRead = await fs.ReadAsync(buffer, 0, 1024);

        Console.WriteLine(Encoding.UTF8.GetString(buffer, 0, bytesRead));
    }

    Console.ReadLine();
}

SyncMain.cs

static void Main()
{
    using (var fs = new FileStream("test.txt", FileMode.Open, FileAccess.Read))
    {
        var buffer = new byte[1024];
        var bytesRead = fs.Read(buffer, 0, 1024);

        Console.WriteLine(Encoding.UTF8.GetString(buffer, 0, bytesRead));
    }

    Console.ReadLine();
}