synchronous upload & download by other client

Hello, sorry for my bad english.

When i'm uploading file, other users can access this not entire file & download it. It will lead to data loss during file transfer, because received file will be broken.

Question: how to prevent other users to download file, while it is not completely upload to server by smartftp program?

Your server would have to create the file with exclusive read/write sharing. From the client side you cannot influence this behavior.