如何确定文件是否仍在通过ftp传输

I have a directory with files that need processing in a batch with PHP. The files are copied on the server via FTP. Some of the files are very big and take a long time to copy. How can I determine in PHP if a file is still being transferred (so I can skip the processing on that file and process it in the next run of the batch process)?I have a directory with files that need process