writing to multiple files asynchronous

Question

I would like to write Async to 2 files some data, i've tried something like this:

private static void Main(string[] args)
{
    FileStream file1 = File.Create(@"D:\test\plik1.dat");
    FileStream file2 = File.Create(@"D:\test\plik2.dat");

    var f1 = await write(file1);
    var f2 = await write(file2);
    for (int i = 0; i < 1024 * 1024; i++)
    {
        if (i % 100 == 0)
            Console.Write("X");
    }
}

private static async Task write(FileStream fs)
{
    var zap = new StreamWriter(fs);
    for (long i = 0; i < 1024 * 1024 * 250; i++)
    {
        zap.WriteAsync("xxx");
    }
}

The compiler error is:

The 'await' operator can only be used within an async method.

how to do it properly?

i would like also to do loop instruction with console.Write("X); as async

can someone help me ? i couldn't find some basic examples on google...

The 'await' operator can only be used within an async method. Consider marking this method with the 'async' modifier and changing its return type to 'Task' — SharkyShark, Aug 16 '17 at 10:53

senz · Answer 1 · 2017-08-16T11:26:41.017

0

Try awaiting your result after the for loop:

private static void Main(string[] args)
{
    FileStream file1 = File.Create(@"D:\test\plik1.dat");
    FileStream file2 = File.Create(@"D:\test\plik2.dat");

    var f1 = Write(file1);
    var f2 = Write(file2);
    var work = DoWork();

    Task.WaitAll(f1,f2,work);
}

private static async Task DoWork()
{
    for (int i = 0; i < 1024 * 1024; i++)
    {
        if (i % 100 == 0)
            Console.Write("X");
    }
}

private static async Task Write(FileStream fs)
{
    var zap = new StreamWriter(fs);
    for (long i = 0; i < 1024 * 1024 * 250; i++)
    {
        await zap.WriteAsync("xxx");
    }
}

edited Aug 16 '17 at 11:26

answered Aug 16 '17 at 10:53

senz

879
10
25

it crashes on Task.WaitAll(f1, f2) with error which says that stream is already used by previous operation on stream... – SharkyShark Aug 16 '17 at 11:00
absolutely. your streams target the same file. you should change the second filename in i.e. `plik2.dat` to avoid this behavior – senz Aug 16 '17 at 11:02
no, i've changed filepath before – SharkyShark Aug 16 '17 at 11:02
first filePath is to plik1.dat, the second is to plik2.dat – SharkyShark Aug 16 '17 at 11:05
1

ah sorry, try to `await zap.WriteAsync("xxx");` – senz Aug 16 '17 at 11:05
thanks, but... how to do the loop whicn do console.write("X") with await – SharkyShark Aug 16 '17 at 11:09
to use `await`, your method must be `async`. it's not possible on the main method. You could use another method like `private async Task Run()` and call `new Program().Run().GetAwaiter().GetResult()` in your main. – senz Aug 16 '17 at 11:11
i updated my answer with another approach. – senz Aug 16 '17 at 11:16

writing to multiple files asynchronous

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