multi target copy

copy.cs

using System.Threading.Channels;

Directory.CreateDirectory("tmp");
if (!File.Exists("tmp/source.a"))
{

    var content = new byte[1024 * 1024 * 1024 + 10];
    new Random().NextBytes(content);
    File.WriteAllBytes("tmp/source.a", content);
}

var buffer = new byte[1024 * 1024];

var channel1 = Channel.CreateBounded<Memory<byte>>(5);
var channel2 = Channel.CreateBounded<Memory<byte>>(5);
var channel3 = Channel.CreateBounded<Memory<byte>>(5);
var channel4 = Channel.CreateBounded<Memory<byte>>(5);

var token = new CancellationTokenSource();

var tasks = new List<Task>();

tasks.Add(FileWriter("tmp/target.a", channel1, token.Token));
//tasks.Add(FileWriter("tmp/target.b", channel2, token.Token));
//tasks.Add(FileWriter("tmp/target.c", channel3, token.Token));
//tasks.Add(FileWriter("tmp/target.d", channel4, token.Token));

var writer1 = channel1.Writer;
var writer2 = channel2.Writer;
var writer3 = channel3.Writer;
var writer4 = channel4.Writer;
using (var streamin = File.OpenRead("tmp/source.a"))
{
    while (streamin.CanRead)
    {
        var bytesread = await streamin.ReadAsync(buffer, 0, buffer.Length);

        var buffer2 = new byte[bytesread];

        buffer.AsMemory().Slice(0, bytesread).CopyTo(buffer2);
        while (!writer1.TryWrite(buffer2.AsMemory())) ;
        //while (!writer2.TryWrite(buffer2.AsMemory())) ;
        //while (!writer3.TryWrite(buffer2.AsMemory())) ;
        //while (!writer4.TryWrite(buffer2.AsMemory())) ;

        if (bytesread < buffer.Length)
        {
            break;
        }

    }
}
writer1.Complete();
//writer2.Complete();
//writer3.Complete();
//writer4.Complete();
Task.WaitAll(tasks.ToArray());

async Task FileWriter(string outfile, Channel<Memory<byte>> channel, CancellationToken cancel)
{
    var reader = channel.Reader;
    using (var output = File.OpenWrite(outfile))
    {
        while (await reader.WaitToReadAsync(cancel))
        {
            var bytes = await reader.ReadAsync(cancel);
            await output.WriteAsync(bytes);
        }
    }
}