Question

Suppose I’m writing a very long string to a file using File.WriteAllText, and another thread or process is trying to read the same file. Would it throw any exception? In other words, what is the FileShare parameter that the File.WriteAllText method uses? It’s not written in the documentation!

Answer 1

This is the source code from .net Framework 4.0. clearly StreamWriter is used that Uses FileShare.Read Internally.

    [SecuritySafeCritical]
public static void WriteAllText(string path, string contents)
{
    if (path == null)
    {
        throw new ArgumentNullException("path");
    }
    if (path.Length == 0)
    {
        throw new ArgumentException(Environment.GetResourceString("Argument_EmptyPath"));
    }
    InternalWriteAllText(path, contents, StreamWriter.UTF8NoBOM);
}


private static void InternalWriteAllText(string path, string contents, Encoding encoding)
{
    using (StreamWriter writer = new StreamWriter(path, false, encoding))
    {
        writer.Write(contents);
    }
}

This is the code that creates the underlying stream for StreamWriter.

private static Stream CreateFile(string path, bool append)
{
    return new FileStream(path, append ? FileMode.Append : FileMode.Create, FileAccess.Write, FileShare.Read, 0x1000, FileOptions.SequentialScan);
}