Add run_once/BYPASS_HOST_LOOP feature in v2

v2/ansible/executor/task_executor.py

@@ -359,6 +359,7 @@ class TaskExecutor:
             loader=self._loader,
             module_loader=self._module_loader,
         )
+
         if not handler:
             raise AnsibleError("the handler '%s' was not found" % handler_name)
 

v2/ansible/plugins/__init__.py

@@ -221,6 +221,9 @@ class PluginLoader:
         path = self.find_plugin(name)
         if path is None:
             return None
+        elif kwargs.get('class_only', False):
+            return getattr(self._module_cache[path], self.class_name)
+
         if path not in self._module_cache:
             self._module_cache[path] = imp.load_source('.'.join([self.package, name]), path)
         return getattr(self._module_cache[path], self.class_name)(*args, **kwargs)

v2/ansible/plugins/strategies/linear.py

@@ -22,6 +22,7 @@ __metaclass__ = type
 from ansible.errors import AnsibleError
 from ansible.executor.play_iterator import PlayIterator
 from ansible.playbook.task import Task
+from ansible.plugins import action_loader
 from ansible.plugins.strategies import StrategyBase
 from ansible.utils.debug import debug
 
@@ -143,8 +144,17 @@ class StrategyModule(StrategyBase):
                     if not task:
                         continue
 
+                    run_once = False
                     work_to_do = True
 
+                    # test to see if the task across all hosts points to an action plugin which
+                    # sets BYPASS_HOST_LOOP to true, or if it has run_once enabled. If so, we
+                    # will only send this task to the first host in the list.
+
+                    action = action_loader.get(task.action, class_only=True)
+                    if task.run_once or getattr(action, 'BYPASS_HOST_LOOP', False):
+                        run_once = True
+
                     debug("getting variables")
                     task_vars = self._variable_manager.get_vars(loader=self._loader, play=iterator._play, host=host, task=task)
                     debug("done getting variables")
@@ -183,6 +193,10 @@ class StrategyModule(StrategyBase):
 
                     self._process_pending_results(iterator)
 
+                    # if we're bypassing the host loop, break out now
+                    if run_once:
+                        break
+
                 debug("done queuing things up, now waiting for results queue to drain")
                 self._wait_on_pending_results(iterator)
 

v2/samples/test_run_once.yml

+- hosts: all
+  gather_facts: no
+  tasks:
+  - ping:
+    run_once: yes
+  - add_host: name=foo