C# .NET: Will a BinaryWriter flush when the FileStream buffer is filled?

I'm coming across something trivial, but it appears that data is flushed to disk (out of the FileStream's buffer) when the data I'm buffering hits the size of the FileStream's buffer.

//use the FileStream buffer to actually buffer the data to be written, so segments are written as desired.
FileStream writeStream = new FileStream(filename, FileMode.Append, FileAccess.Write, FileShare.None, CommandOperationBufferSize);
BinaryWriter binWriter = new BinaryWriter(writeStream);
byte[] FullSize = new byte[CommandOperationTotalSize];

//the BinaryWriter will flush when the FileStream buffer is hit
binWriter.Write(FullSize); //DATA FLUSHES TO DISK HERE!

//if wait, wait five seconds
if (CommandOperation == "writewait" || CommandOperation == "appendwait")
{
    Thread.Sleep(5000);
    wr开发者_开发百科iteStream.Flush();
    Thread.Sleep(5000);
}

writeStream.Close();
writeStream.Dispose();
binWriter.Close();

Can anyone confirm that this is the case? That the FileStream's buffer is actual .Flush() when the FileStream's buffer is filled?

I ask because it appears that if I set CommandOperationTotalSize to 1MB, and set the CommandOperationBufferSize to 64KB, data is flushed to disk when the buffer is filled.

Sounds like I answered my own question, but it seems odd that the FileStream buffer wouldn't just overflow? But maybe the API developers are trying to be nice?

Thanks,

Matt

You can readily assume that overflowing the buffer is not possible. The class would be rather hard to use if that was the case, given that FileStream has no properties at all to tell you how much is currently being buffered.

The buffer is only there to reduce the number of calls to the native Windows WriteFile() call. Important when you write small amounts of data, say one byte at a time. If you don't explicitly specify the buffer size then it will use a buffer of 4096 bytes. Which is fine, it is very rare to need something else. Any writes are further buffered by the file system cache. You should only consider a non-standard size when you use FileOptions.WriteThrough