Why doesn't text get written to disk?

Question

I have the following C# code:

private const int APPENDBUFFERSIZE = 65536;
private StreamWriter _streamWriter;
private FileStream _fileStream;
private BufferedStream _bufferedStream;

public void Open(string fileName)
{
    _fileStream = File.Open(fileName, FileMode.Create, FileAccess.Write, FileShare.Read);
    _bufferedStream = new BufferedStream(_fileStream, APPENDBUFFERSIZE);
    _streamWriter = new StreamWriter(_bufferedStream);
}

public void Write(string data)
{
    _streamWriter.Write(data);
}

public void Close()
{
    if (_streamWriter != null)
    {
        _streamWriter.Flush();
        _streamWriter.Dispose();
        _streamWriter = null;
    }
    if (_bufferedStream != null)
    {
        _bufferedStream.Dispose();
        _bufferedStream = null;
    }
    if (_fileStream != null)
    {
        _fileStream.Dispose();
        _fileStream = null;
    }
}

Why doesn't the data get written to disk until I call Close? Technical data: I write 9000 KB worth of data

StreamWriter class has:

internal const int DefaultBufferSize = 1024;

FileStream class has:

internal const int DefaultBufferSize = 4096;

BufferedStream should be 65536 bytes. filename is a full path to a file on my local drive D.

filename = "D:\\Folder1\Folder2\\file.txt"

And I do have permissions to write to it. For a call to Write I use something similar to:

data = "1234567889|ababababababababbabababababababababababab"

Also, I don't want to get rid of the buffer, I just want the stream to be flushed every now and then, and see it on disk. It's weird to have the file to 0 KB and all of the sudden when you close, it's big. So by all measurements, all the buffers should overflow unless written to next stream/disk. Still, Windows only shows file size greater than 0 KB, after Close, although I've waited a few minutes after the writing to file has finished.

Any ideas?

Thanks, Ciprian.

UPDATE: The size appears 0 in windows explorer size column. If I look at file properties, then the size is larger than 0(which is correct). After I return from the properties window and refresh the windows explorer window, the size column gets updated to a value larger than 0. I I just refresh the windows explorer window without looking at file properties, the size column stays at 0. Also if I open the file with notepad++, it has all the data, and a refresh on the windows explorer window shows the correct value in the size column. So my issue is probably not due to the code I wrote, but you never know.

where are you writing the data are you just trying to write empty charcter for the whole thing? — johnny 5, Oct 14 '15 at 18:01
On my own PC. filename is smth like: D:\Folder1\Folder2\file.txt data is like "09890890|ajhdjaskdhaskdjhaskdhasjkdhasksjdha" for each call to Write — MciprianM, Oct 14 '15 at 18:03
I've not tried it, but you could try File.Create with the [WriteThrough](https://msdn.microsoft.com/en-us/library/system.io.fileoptions(v=vs.110).aspx) option. — 001, Oct 14 '15 at 18:05
I don't want to get rid of the buffer, I just want to flush when it's supposed to. — MciprianM, Oct 14 '15 at 18:07
It could be the file system cache causing your issue. The .NET buffering is probably working as expected. — 001, Oct 14 '15 at 18:11

score 2 · Answer 1 · answered Oct 14 '15 at 18:15

Straight from the horse's mouth (aka MSDN):

Adds a buffering layer to read and write operations on another stream. This class cannot be inherited.

And further down in the remarks section:

A buffer is a block of bytes in memory used to cache data, thereby reducing the number of calls to the operating system

https://msdn.microsoft.com/en-us/library/system.io.bufferedstream(v=vs.110).aspx

So based on the documentation, your code is behaving as expected. Nothing will get written to disk unless one of 3 events occur:

You Close() the buffered stream
You Flush() it
The buffer gets full

HTH...

Xavier J · Answer 2 · 2015-10-14T18:15:15.277

0

You used a BufferedStream, which is not going to flush anything until you've reached 65536 bytes in the buffer, OR you call the Flush method, OR your call the Close method. If you want results sooner, take out the BufferedStream or change its size to a smaller number.

ONLY when the StreamWriter flushes (or closes), it writes to the BufferedStream, and ONLY when the BufferedStream flushes (or closes), it writes to the FileStream.

Additionally, the Windows (device) file buffer needs to do its magic AFTER .NET processing, and ultimately you have no control over when it actually persists data to the device.

edited Oct 14 '15 at 18:15

answered Oct 14 '15 at 18:03

Xavier J

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He stated he's writing 9000kb of data and is wondering why it doesn't flush since the buffer is 65536 bytes. – Dave Zych Oct 14 '15 at 18:06
There is ALSO the file system buffer, which we have no direct control of. – Xavier J Oct 14 '15 at 18:09
Write... and that's probably what the problem is so you should probably add that to your answer. – Dave Zych Oct 14 '15 at 18:12
I'll leave it over night with more data and see if anything changes. – MciprianM Oct 14 '15 at 18:13

Why doesn't text get written to disk?

2 Answers2