[modules/redshift] Update in separate thread

Move updating of redshift information into a separate thread so that
errors like missing network connectivity do not block the whole status
bar.

fixes #61

bumblebee/modules/redshift.py

@@ -6,43 +6,78 @@ Requires the following executable:
     * redshift
 """
 
+import threading
+
 import bumblebee.input
 import bumblebee.output
 import bumblebee.engine
 
+def is_terminated():
+    for thread in threading.enumerate():
+        if thread.name == "MainThread" and not thread.is_alive():
+            return True
+    return False
+
+def get_redshift_value(widget):
+    while True:
+        if is_terminated():
+            return
+        widget.get("condition").acquire()
+        while True:
+            try:
+                widget.get("condition").wait(1)
+            except RuntimeError:
+                continue
+            break
+
+        try:
+            res = bumblebee.util.execute("redshift -p")
+        except Exception:
+            res = ""
+            widget.set("temp", "n/a")
+            widget.set("transition", None)
+        for line in res.split("\n"):
+            if "temperature" in line.lower():
+                widget.set("temp", line.split(" ")[2])
+            if "period" in line.lower():
+                state = line.split(" ")[1].lower()
+                if "day" in state:
+                    widget.set("state", "day")
+                elif "night" in state:
+                    widget.set("state", "night")
+                else:
+                    widget.set("state", "transition")
+                    widget.set("transition", " ".join(line.split(" ")[2:]))
+        widget.get("condition").release()
+
 class Module(bumblebee.engine.Module):
     def __init__(self, engine, config):
-        super(Module, self).__init__(engine, config,
-            bumblebee.output.Widget(full_text=self.text)
-        )
+        widget = bumblebee.output.Widget(full_text=self.text)
+        super(Module, self).__init__(engine, config, widget)
         self._text = ""
-        self._state = "transition"
+        self._condition = threading.Condition()
+        widget.set("condition", self._condition)
+        self._thread = threading.Thread(target=get_redshift_value, args=(widget,))
+        self._thread.start()
+        self._condition.acquire()
+        self._condition.notify()
+        self._condition.release()
 
     def text(self, widget):
         return "{}".format(self._text)
 
     def update(self, widgets):
-        result = bumblebee.util.execute("redshift -p")
-
-        temp = ""
-        transition = ""
-        for line in result.split("\n"):
-            if "temperature" in line.lower():
-                temp = line.split(" ")[2]
-            if "period" in line.lower():
-                state = line.split(" ")[1].lower()
-                if "day" in state:
-                    self._state = "day"
-                elif "night" in state:
-                    self._state = "night"
-                else:
-                    self._state = "transition"
-                    transition = " ".join(line.split(" ")[2:])
+        widget = widgets[0]
+        self._condition.acquire()
+        self._condition.notify()
+        self._condition.release()
+        temp = widget.get("temp", "n/a")
         self._text = temp
+        transition = widget.get("transition", None)
         if transition:
             self._text = "{} {}".format(temp, transition)
 
     def state(self, widget):
-        return self._state
+        return widget.get("state", None)
 
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