Timer job with minute schedule and multiple instances.

I have a sharepoint timer job that runs every 1 minute, In timer job execute method I am uploading a large file to a remote server, If file uploading takes more than 1 minute and another instance of time job runs meanwhile, then what happens?

 - Existing instance will continue uplanding the file.
 - Existing instance will be stopped and new instance will start uploading the file.
 - Both instances will be running in a queue.