set all tracker thread to deamon

tracker/rabit_demo.py

@@ -51,6 +51,7 @@ def mthread_submit(nslave, worker_args):
     procs = {}
     for i in range(nslave):
         procs[i] = Thread(target = exec_cmd, args = (args.command + worker_args, i))
+        procs[i].daemon = True
         procs[i].start()
     for i in range(nslave):
         procs[i].join()

tracker/rabit_tracker.py

@@ -257,6 +257,7 @@ class Tracker:
 def submit(nslave, args, fun_submit, verbose):
     master = Tracker(verbose = verbose)
     submit_thread = Thread(target = fun_submit, args = (nslave, args + master.slave_args()))
+    submit_thread.daemon = True
     submit_thread.start()
     master.accept_slaves(nslave)
     submit_thread.join()