Require blocking IO for ansible CLI.

changelogs/fragments/ansible-require-blocking-io.yml

@@ -0,0 +1,3 @@
+minor_changes:
+  - ansible - At startup the stdin/stdout/stderr file handles are checked to verify they are using blocking IO.
+              If not, the process exits with an error reporting which file handle(s) are using non-blocking IO.

lib/ansible/cli/__init__.py

@@ -7,6 +7,7 @@
 from __future__ import (absolute_import, division, print_function)
 __metaclass__ = type
 
+import os
 import sys
 
 # Used for determining if the system is running a new enough python version
@@ -17,6 +18,28 @@ if sys.version_info < (3, 8):
         'Current version: %s' % ''.join(sys.version.splitlines())
     )
 
+
+def check_blocking_io():
+    """Check stdin/stdout/stderr to make sure they are using blocking IO."""
+    handles = []
+
+    for handle in (sys.stdin, sys.stdout, sys.stderr):
+        # noinspection PyBroadException
+        try:
+            fd = handle.fileno()
+        except Exception:
+            continue  # not a real file handle, such as during the import sanity test
+
+        if not os.get_blocking(fd):
+            handles.append(getattr(handle, 'name', None) or '#%s' % fd)
+
+    if handles:
+        raise SystemExit('ERROR: Ansible requires blocking IO on stdin/stdout/stderr. '
+                         'Non-blocking file handles detected: %s' % ', '.join(_io for _io in handles))
+
+
+check_blocking_io()
+
 from importlib.metadata import version
 from ansible.module_utils.compat.version import LooseVersion
 
@@ -31,7 +54,6 @@ if jinja2_version < LooseVersion('3.0'):
 
 import errno
 import getpass
-import os
 import subprocess
 import traceback
 from abc import ABC, abstractmethod