how does filestream insert record but an proud lock?

what i'm perplexing filestream c#/.net open twin streams: appending record reading those writes asynchronously (for section contrast network tie doing code). i can't figure out writer tide open record non-exlusive locking mode so formula always throws an exception:

the slight can't opening file
'c:\test.txt' since being used
another process.

here's smattering formula demonstrates issue:

filestream fwriter = new filestream("c:\\test.txt", filemode.append,
    fileaccess.write, fileshare.read);
filestream freader = new filestream("c:\\test.txt", filemode.open,
    fileaccess.read, fileshare.read);