using WinAPI functions in C#

Question

I want to get messages posted by a button control using a thread while the program continue the execution of another process.This process should be ended while the user clicks the button.This process is a file reading process.At least process should read the file which is started to be read,but shouldn't read any more files when the button is clicked. I import the user32.dll and I used WinAPI GetMessage function but it didn't work.Can anyone help me? Thanks in advance...