from threading import Thread

class CtrlThread (Thread):
    def __init__(self, editfile):
        Thread.__init__(self)
        self.editfile = editfile

     def run (self):
        subprocess.call(["/usr/bin/mvim", "-g", "--remote-tab-silent",self.editfile])

tr = CtrlThread(editfile)
 tr.start()

def run (self):
    p = subprocess.Popen(["/usr/bin/mvim", "-g", "--remote-tab-silent" ,self.editfile])
    print("Pid: ", p.pid)

Pid: 1699

USER  PID   ...  COMMAND
user 1699   ...  (Vim)
user 1702   ...  /Applications/MacVim.app/Contents/MacOS/Vim -f -g -g --remote-tab-silent /path/to/file