DefaultEventLoopPolicy: raise NotImplementedError, not RecursionError

Since the DefaultEventLoopPolicy wraps the underlying asyncio event
loop policy, raise NotImplementedError if the current instance is set
as the underlying event loop policy. This avoids a RecursionError
that would flood the terminal with a large stack trace.

2 files changed, 25 insertions, 4 deletions

diff --git a/pym/portage/util/futures/_asyncio/__init__.py b/pym/portage/util/futures/_asyncio/__init__.py
index 940da4762..acfd59396 100644
--- a/pym/portage/util/futures/_asyncio/__init__.py
+++ b/pym/portage/util/futures/_asyncio/__init__.py
@@ -32,7 +32,7 @@ except ImportError:
 
 import portage
 portage.proxy.lazyimport.lazyimport(globals(),
-	'portage.util.futures.unix_events:DefaultEventLoopPolicy',
+	'portage.util.futures.unix_events:_PortageEventLoopPolicy',
 )
 from portage.util._eventloop.asyncio_event_loop import AsyncioEventLoop as _AsyncioEventLoop
 from portage.util._eventloop.global_event_loop import (
@@ -67,7 +67,7 @@ def get_event_loop_policy():
 	global _lock, _policy
 	with _lock:
 		if _policy is None:
-			_policy = DefaultEventLoopPolicy()
+			_policy = _PortageEventLoopPolicy()
 		return _policy
 
 
@@ -81,7 +81,7 @@ def set_event_loop_policy(policy):
 	"""
 	global _lock, _policy
 	with _lock:
-		_policy = policy or DefaultEventLoopPolicy()
+		_policy = policy or _PortageEventLoopPolicy()
 
 
 def get_event_loop():
diff --git a/pym/portage/util/futures/unix_events.py b/pym/portage/util/futures/unix_events.py
index 8eb369f8b..3381eaa7d 100644
--- a/pym/portage/util/futures/unix_events.py
+++ b/pym/portage/util/futures/unix_events.py
@@ -681,4 +681,25 @@ class _PortageEventLoopPolicy(events.AbstractEventLoopPolicy):
 		return _global_event_loop()._asyncio_child_watcher
 
 
-DefaultEventLoopPolicy = _PortageEventLoopPolicy
+class _AsyncioEventLoopPolicy(_PortageEventLoopPolicy):
+	"""
+	A subclass of _PortageEventLoopPolicy which raises
+	NotImplementedError if it is set as the real asyncio event loop
+	policy, since this class is intended to *wrap* the real asyncio
+	event loop policy.
+	"""
+	def _check_recursion(self):
+		if _real_asyncio.get_event_loop_policy() is self:
+			raise NotImplementedError('this class is only a wrapper')
+
+	def get_event_loop(self):
+		self._check_recursion()
+		return super(_AsyncioEventLoopPolicy, self).get_event_loop()
+
+	def get_child_watcher(self):
+		self._check_recursion()
+		return super(_AsyncioEventLoopPolicy, self).get_child_watcher()
+
+
+DefaultEventLoopPolicy = (_AsyncioEventLoopPolicy if _asyncio_enabled
+	else _PortageEventLoopPolicy)