Store hosts for a play as a play attribute

Operate on that play attribute to make things faster for larger
inventories. Instead of making a round trip through inventory.list_hosts
and working through some lengthy list comprehensions over and over
again, calculate the potenital hosts for a play once, then reduce from
it the unavailable hosts when necessary.

Also moves how the %fail is done. The host count is a play level count
of available hosts, which then is compared after each task to the
current number of available hosts for the play. This used to get a new
count every task which was also time expensive.

lib/ansible/playbook/__init__.py

@@ -289,17 +289,17 @@ class PlayBook(object):
 
     # *****************************************************
 
-    def _list_available_hosts(self, *args):
+    def _trim_unavailable_hosts(self, hostlist=[]):
         ''' returns a list of hosts that haven't failed and aren't dark '''
 
-        return [ h for h in self.inventory.list_hosts(*args) if (h not in self.stats.failures) and (h not in self.stats.dark)]
+        return [ h for h in hostlist if (h not in self.stats.failures) and (h not in self.stats.dark)]
 
     # *****************************************************
 
     def _run_task_internal(self, task):
         ''' run a particular module step in a playbook '''
 
-        hosts = self._list_available_hosts()
+        hosts = self._trim_unavailable_hosts(task.play._play_hosts)
         self.inventory.restrict_to(hosts)
 
         runner = ansible.runner.Runner(
@@ -436,7 +436,7 @@ class PlayBook(object):
         if play.gather_facts is False:
             return {}
 
-        host_list = self._list_available_hosts(play.hosts)
+        host_list = self._trim_unavailable_hosts(play._play_hosts)
 
         self.callbacks.on_setup()
         self.inventory.restrict_to(host_list)
@@ -499,8 +499,10 @@ class PlayBook(object):
         ''' run a list of tasks for a given pattern, in order '''
 
         self.callbacks.on_play_start(play.name)
+        # Get the hosts for this play
+        play._play_hosts = self.inventory.list_hosts(play.hosts)
         # if no hosts matches this play, drop out
-        if not self.inventory.list_hosts(play.hosts):
+        if not play._play_hosts:
             self.callbacks.on_no_hosts_matched()
             return True
 
@@ -509,8 +511,9 @@ class PlayBook(object):
 
         # now with that data, handle contentional variable file imports!
 
-        all_hosts = self._list_available_hosts(play.hosts)
+        all_hosts = self._trim_unavailable_hosts(play._play_hosts)
         play.update_vars_files(all_hosts)
+        hosts_count = len(all_hosts)
 
         serialized_batch = []
         if play.serial <= 0:
@@ -526,6 +529,9 @@ class PlayBook(object):
 
         for on_hosts in serialized_batch:
 
+            # restrict the play to just the hosts we have in our on_hosts block that are
+            # available.
+            play._play_hosts = self._trim_unavailable_hosts(on_hosts)
             self.inventory.also_restrict_to(on_hosts)
 
             for task in play.tasks():
@@ -548,7 +554,7 @@ class PlayBook(object):
                                 # prevent duplicate handler includes from running more than once
                                 fired_names[handler_name] = 1
 
-                                host_list = self._list_available_hosts(play.hosts)
+                                host_list = self._trim_unavailable_hosts(play._play_hosts)
                                 if handler.any_errors_fatal and len(host_list) < hosts_count:
                                     play.max_fail_pct = 0
                                 if (hosts_count - len(host_list)) > int((play.max_fail_pct)/100.0 * hosts_count):
@@ -567,8 +573,6 @@ class PlayBook(object):
 
                         continue
 
-                hosts_count = len(self._list_available_hosts(play.hosts))
-
                 # only run the task if the requested tags match
                 should_run = False
                 for x in self.only_tags:
@@ -591,7 +595,9 @@ class PlayBook(object):
                         # just didn't match anything and that's ok
                         return False
 
-                host_list = self._list_available_hosts(play.hosts)
+                # Get a new list of what hosts are left as available, the ones that
+                # did not go fail/dark during the task
+                host_list = self._trim_unavailable_hosts(play._play_hosts)
 
                 # Set max_fail_pct to 0, So if any hosts fails, bail out
                 if task.any_errors_fatal and len(host_list) < hosts_count:

lib/ansible/playbook/play.py

@@ -34,7 +34,7 @@ class Play(object):
        'handlers', 'remote_user', 'remote_port', 'included_roles', 'accelerate',
        'accelerate_port', 'accelerate_ipv6', 'sudo', 'sudo_user', 'transport', 'playbook',
        'tags', 'gather_facts', 'serial', '_ds', '_handlers', '_tasks',
-       'basedir', 'any_errors_fatal', 'roles', 'max_fail_pct'
+       'basedir', 'any_errors_fatal', 'roles', 'max_fail_pct', '_play_hosts'
     ]
 
     # to catch typos and so forth -- these are userland names
@@ -134,6 +134,8 @@ class Play(object):
         if self.sudo_user != 'root':
             self.sudo = True
 
+        # place holder for the discovered hosts to be used in this play
+        self._play_hosts = None
 
     # *************************************************