Question

Lets say for example I had a 20gb file and I decided to copy it to “c:/folder/filename.ext”. Obviously this would take some time to complete.

What would the the following return if it was executed whilst the copy was taking place?

File.Exists("c:/folder/filename.ext");

Answer 1

What would the the following return if it was executed whilst the copy was taking place?

Assuming the process you are running your code under has sufficient privileges to read the file it will return True (don’t forget that File.Exists returns False if the account doesn’t have sufficient privileges to read the file even if the file exists). The File.Exists method doesn’t care if the file is currently being written to or read from:

public class Program
{
    static void Main()
    {
        Task.Factory.StartNew(() =>
        {
            using (var stream = File.OpenWrite("test.dat"))
            {
                Thread.Sleep(100);
            }
        });
        Thread.Sleep(10);

        // prints True
        Console.WriteLine(File.Exists("test.dat"));
    }
}