Add new host_pinned strategy (#44586)

The 'free' strategy still attempts to do all hosts per task before going to the next, it just doesn't wait for slow hosts,
This strategy processes each host as fast as possible to the end of the play before trying to process another host in the pool.

lib/ansible/plugins/strategy/free.py

@@ -58,6 +58,10 @@ class StrategyModule(StrategyBase):
         return [host for host in notified_hosts
                 if host in self._flushed_hosts and self._flushed_hosts[host]]
 
+    def __init__(self, tqm):
+        super(StrategyModule, self).__init__(tqm)
+        self._host_pinned = False
+
     def run(self, iterator, play_context):
         '''
         The "free" strategy is a bit more complex, in that it allows tasks to
@@ -77,6 +81,9 @@ class StrategyModule(StrategyBase):
 
         result = self._tqm.RUN_OK
 
+        # start with all workers being counted as being free
+        workers_free = len(self._workers)
+
         work_to_do = True
         while work_to_do and not self._tqm._terminated:
 
@@ -167,10 +174,18 @@ class StrategyModule(StrategyBase):
                                                     "as tasks are executed independently on each host")
                                 self._tqm.send_callback('v2_playbook_on_task_start', task, is_conditional=False)
                                 self._queue_task(host, task, task_vars, play_context)
+                                # each task is counted as a worker being busy
+                                workers_free -= 1
                                 del task_vars
                     else:
                         display.debug("%s is blocked, skipping for now" % host_name)
 
+                # all workers have tasks to do (and the current host isn't done with the play).
+                # loop back to starting host and break out
+                if self._host_pinned and workers_free == 0 and work_to_do:
+                    last_host = starting_host
+                    break
+
                 # move on to the next host and make sure we
                 # haven't gone past the end of our hosts list
                 last_host += 1
@@ -184,6 +199,9 @@ class StrategyModule(StrategyBase):
             results = self._process_pending_results(iterator)
             host_results.extend(results)
 
+            # each result is counted as a worker being free again
+            workers_free += len(results)
+
             self.update_active_connections(results)
 
             try: