issue #360: ansible: missing lock around ContextService.put().

ansible_mitogen/services.py

@@ -139,11 +139,15 @@ class ContextService(mitogen.service.Service):
         count reaches zero.
         """
         LOG.debug('%r.put(%r)', self, context)
+        self._lock.acquire()
+        try:
             if self._refs_by_context.get(context, 0) == 0:
                 LOG.warning('%r.put(%r): refcount was 0. shutdown_all called?',
                             self, context)
                 return
             self._refs_by_context[context] -= 1
+        finally:
+            self._lock.release()
 
     def key_from_kwargs(self, **kwargs):
         """