Make interprocess polling interval configurable (ansible#16560)

As recently there was back-and-forth with this hardcoded value
(0.001 -> 0.01 -> 0.005), obviousely the optimal value for it depends on
Ansible usage scanario and is better to be configurable.

This patch adds a new config option in DEFAULT section,
`internal_poll_interval`, with default of 0.001 corresponding to the
value hardcoded in Ansible v2.1.
This config option is then used instead of hardcoded values where
needed.

Related GH issue: 14219

docsite/rst/intro_configuration.rst

@@ -432,6 +432,20 @@ implications and wish to disable it, you may do so here by setting the value to
 
     host_key_checking=True
 
+.. _internal_poll_interval:
+
+internal_poll_interval
+======================
+
+.. versionadded:: 2.2
+
+This sets the interval (in seconds) of Ansible internal processes polling each other.
+Lower values improve performance with large playbooks at the expense of extra CPU load.
+Higher values are more suitable for Ansible usage in automation scenarios, when UI responsiveness is not required but CPU usage might be a concern.
+Default corresponds to the value hardcoded in Ansible ≤ 2.1::
+
+    internal_poll_interval=0.001
+
 .. _inventory_file:
 
 inventory

lib/ansible/constants.py

@@ -146,7 +146,7 @@ def load_config_file():
 DEFAULTS='defaults'
 
 # FIXME: add deprecation warning when these get set
-#### DEPRECATED VARS #### 
+#### DEPRECATED VARS ####
 # use more sanely named 'inventory'
 DEPRECATED_HOST_LIST  = get_config(p, DEFAULTS, 'hostfile', 'ANSIBLE_HOSTS', '/etc/ansible/hosts', ispath=True)
 # this is not used since 0.5 but people might still have in config
@@ -195,6 +195,7 @@ def load_config_file():
 DEFAULT_FORCE_HANDLERS    = get_config(p, DEFAULTS, 'force_handlers', 'ANSIBLE_FORCE_HANDLERS', False, boolean=True)
 DEFAULT_INVENTORY_IGNORE  = get_config(p, DEFAULTS, 'inventory_ignore_extensions', 'ANSIBLE_INVENTORY_IGNORE', ["~", ".orig", ".bak", ".ini", ".cfg", ".retry", ".pyc", ".pyo"], islist=True)
 DEFAULT_VAR_COMPRESSION_LEVEL = get_config(p, DEFAULTS, 'var_compression_level', 'ANSIBLE_VAR_COMPRESSION_LEVEL', 0, integer=True)
+DEFAULT_INTERNAL_POLL_INTERVAL = get_config(p, DEFAULTS, 'internal_poll_interval', None, 0.001, floating=True)
 
 # static includes
 DEFAULT_TASK_INCLUDES_STATIC    = get_config(p, DEFAULTS, 'task_includes_static', 'ANSIBLE_TASK_INCLUDES_STATIC', False, boolean=True)

lib/ansible/plugins/strategy/__init__.py

@@ -26,6 +26,7 @@
 from multiprocessing import Lock
 from jinja2.exceptions import UndefinedError
 
+from ansible import constants as C
 from ansible.compat.six.moves import queue as Queue
 from ansible.compat.six import iteritems, string_types
 from ansible.errors import AnsibleError, AnsibleParserError, AnsibleUndefinedVariable
@@ -530,7 +531,7 @@ def _wait_on_pending_results(self, iterator):
             results = self._process_pending_results(iterator)
             ret_results.extend(results)
             if self._pending_results > 0:
-                time.sleep(0.001)
+                time.sleep(C.DEFAULT_INTERNAL_POLL_INTERVAL)
 
         display.debug("no more pending results, returning what we have")
 

lib/ansible/plugins/strategy/free.py

@@ -21,6 +21,7 @@
 
 import time
 
+from ansible import constants as C
 from ansible.errors import AnsibleError
 from ansible.playbook.included_file import IncludedFile
 from ansible.plugins import action_loader
@@ -202,7 +203,7 @@ def run(self, iterator, play_context):
                 display.debug("done adding collected blocks to iterator")
 
             # pause briefly so we don't spin lock
-            time.sleep(0.001)
+            time.sleep(C.DEFAULT_INTERNAL_POLL_INTERVAL)
 
         # collect all the final results
         results = self._wait_on_pending_results(iterator)