[core] Execution contexts are now context managers.

bonobo/execution/base.py

@@ -58,6 +58,13 @@ class LoopingExecutionContext(Wrapper):
         # XXX enhancers
         self._enhancers = get_enhancers(self.wrapped)
 
+    def __enter__(self):
+        self.start()
+        return self
+
+    def __exit__(self, exc_type=None, exc_val=None, exc_tb=None):
+        self.stop()
+
     def start(self):
         if self.started:
             raise RuntimeError('Cannot start a node twice ({}).'.format(get_name(self)))

bonobo/strategies/executor.py

@@ -1,6 +1,5 @@
 import time
 import traceback
-
 from concurrent.futures import Executor, ProcessPoolExecutor, ThreadPoolExecutor
 
 from bonobo.constants import BEGIN, END
@@ -29,19 +28,16 @@ class ExecutorStrategy(Strategy):
         futures = []
 
         for plugin_context in context.plugins:
-
             def _runner(plugin_context=plugin_context):
+                with plugin_context:
                     try:
-                    plugin_context.start()
                         plugin_context.loop()
-                    plugin_context.stop()
                     except Exception as exc:
                         print_error(exc, traceback.format_exc(), context=plugin_context)
 
             futures.append(executor.submit(_runner))
 
         for node_context in context.nodes:
-
             def _runner(node_context=node_context):
                 try:
                     node_context.start()