Why do you want to empty that file when it is in use. You have mentioned about “without stopping process”, so I guess the process is important, hence th log file which is written by the process as well. Can you give some more details on what you are trying to do ?
I need to empty some file because we have limited space on our system drive and we don’t have control to the application that create these files. I think these files are not important because they ara stores on temp folder and they are too big to be open with notepad for example. I belive there are a third-party windows service blocking the file and that’s why I want to clear these files.