Started seting the running flag immediately on the call to start()

instead of after all the startup tsks are done. This alleviates a potential
problem where start() could be called more than once in quick succession
with unpredictable results.

pipeline/__init__.py

@@ -56,7 +56,11 @@ class Pipeline:
         self.logger = logging.getLogger('play-daemon.pipeline')
 
     def start(self):
+        if self.running:
+            raise Exception("Already running!")
+        self.running = True
         self.logger.info('Starting')
+
         for item in os.scandir(self.config['Pipeline']['tempdir']):
             shutil.rmtree(item)
         self.workthread = WorkThread(int(self.config['Pool']['capacity']))
@@ -91,7 +95,6 @@ class Pipeline:
             preprocessor.start()
         self.watcher.start()
 
-        self.running = True
         self.logger.debug('Started')
 
     def stop(self):
@@ -99,8 +102,6 @@ class Pipeline:
         if not self.running:
             raise Exception("Not running!")
 
-        self.running = False
-
         self.watcher.shutdown()
         for preprocessor in self.preprocessors.values():
             preprocessor.shutdown()
@@ -112,3 +113,4 @@ class Pipeline:
         self.notifier.shutdown()
 
         self.logger.debug('Stopped')
+        self.running = False