[modules/ping] Spawn thread on-the-fly

Instead of having a thread that runs in the background continuously,
spawn a new one for every update interval. That speeds up the tests
quite a lot.

see #23

bumblebee/modules/ping.py

@@ -20,24 +20,11 @@ import bumblebee.output
 import bumblebee.engine
 
 def get_rtt(module, widget):
-
-    main = None
-    for thread in threading.enumerate():
-        if thread.name == "MainThread":
-            main = thread
-
-    interval = widget.get("interval")
-    next_check = 0
-    while main.is_alive():
     try:
-            if int(time.time()) < next_check:
-                time.sleep(1)
-                continue
         widget.set("rtt-unreachable", False)
         res = bumblebee.util.execute("ping -n -q -c {} -W {} {}".format(
             widget.get("rtt-probes"), widget.get("rtt-timeout"), widget.get("address")
         ))
-            next_check = int(time.time()) + interval
 
         for line in res.split("\n"):
             if not line.startswith("rtt"): continue
@@ -62,8 +49,7 @@ class Module(bumblebee.engine.Module):
         widget.set("rtt-avg", 0.0)
         widget.set("rtt-unit", "")
 
-        self._thread = threading.Thread(target=get_rtt, args=(self,widget,))
-        self._thread.start()
+        self._next_check = 0
 
     def rtt(self, widget):
         if widget.get("rtt-unreachable"):
@@ -78,4 +64,11 @@ class Module(bumblebee.engine.Module):
         if widget.get("rtt-unreachable"): return ["critical"]
         return self.threshold_state(widget.get("rtt-avg"), 1000.0, 2000.0)
 
+    def update(self, widgets):
+        if int(time.time()) < self._next_check:
+            return
+        thread = threading.Thread(target=get_rtt, args=(self,widgets[0],))
+        thread.start()
+        self._next_check = int(time.time()) + widgets[0].get("interval")
+
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