Issue #25593: Change semantics of EventLoop.stop().
diff --git a/Lib/asyncio/base_events.py b/Lib/asyncio/base_events.py
index af9c881..c5ffad4 100644
--- a/Lib/asyncio/base_events.py
+++ b/Lib/asyncio/base_events.py
@@ -70,10 +70,6 @@
return repr(fd)
-class _StopError(BaseException):
- """Raised to stop the event loop."""
-
-
def _check_resolved_address(sock, address):
# Ensure that the address is already resolved to avoid the trap of hanging
# the entire event loop when the address requires doing a DNS lookup.
@@ -118,9 +114,6 @@
"got host %r: %s"
% (host, err))
-def _raise_stop_error(*args):
- raise _StopError
-
def _run_until_complete_cb(fut):
exc = fut._exception
@@ -129,7 +122,7 @@
# Issue #22429: run_forever() already finished, no need to
# stop it.
return
- _raise_stop_error()
+ fut._loop.stop()
class Server(events.AbstractServer):
@@ -184,6 +177,7 @@
def __init__(self):
self._timer_cancelled_count = 0
self._closed = False
+ self._stopping = False
self._ready = collections.deque()
self._scheduled = []
self._default_executor = None
@@ -298,11 +292,11 @@
self._thread_id = threading.get_ident()
try:
while True:
- try:
- self._run_once()
- except _StopError:
+ self._run_once()
+ if self._stopping:
break
finally:
+ self._stopping = False
self._thread_id = None
self._set_coroutine_wrapper(False)
@@ -345,11 +339,10 @@
def stop(self):
"""Stop running the event loop.
- Every callback scheduled before stop() is called will run. Callbacks
- scheduled after stop() is called will not run. However, those callbacks
- will run if run_forever is called again later.
+ Every callback already scheduled will still run. This simply informs
+ run_forever to stop looping after a complete iteration.
"""
- self.call_soon(_raise_stop_error)
+ self._stopping = True
def close(self):
"""Close the event loop.
@@ -1194,7 +1187,7 @@
handle._scheduled = False
timeout = None
- if self._ready:
+ if self._ready or self._stopping:
timeout = 0
elif self._scheduled:
# Compute the desired timeout.
diff --git a/Lib/asyncio/test_utils.py b/Lib/asyncio/test_utils.py
index 8cee95b..e06ac06 100644
--- a/Lib/asyncio/test_utils.py
+++ b/Lib/asyncio/test_utils.py
@@ -71,12 +71,13 @@
def run_once(loop):
- """loop.stop() schedules _raise_stop_error()
- and run_forever() runs until _raise_stop_error() callback.
- this wont work if test waits for some IO events, because
- _raise_stop_error() runs before any of io events callbacks.
+ """Legacy API to run once through the event loop.
+
+ This is the recommended pattern for test code. It will poll the
+ selector once and run all callbacks scheduled in response to I/O
+ events.
"""
- loop.stop()
+ loop.call_soon(loop.stop)
loop.run_forever()
diff --git a/Lib/test/test_asyncio/test_base_events.py b/Lib/test/test_asyncio/test_base_events.py
index 54b771e..072fe2f 100644
--- a/Lib/test/test_asyncio/test_base_events.py
+++ b/Lib/test/test_asyncio/test_base_events.py
@@ -757,6 +757,59 @@
pass
self.assertTrue(func.called)
+ def test_single_selecter_event_callback_after_stopping(self):
+ # Python issue #25593: A stopped event loop may cause event callbacks
+ # to run more than once.
+ event_sentinel = object()
+ callcount = 0
+ doer = None
+
+ def proc_events(event_list):
+ nonlocal doer
+ if event_sentinel in event_list:
+ doer = self.loop.call_soon(do_event)
+
+ def do_event():
+ nonlocal callcount
+ callcount += 1
+ self.loop.call_soon(clear_selector)
+
+ def clear_selector():
+ doer.cancel()
+ self.loop._selector.select.return_value = ()
+
+ self.loop._process_events = proc_events
+ self.loop._selector.select.return_value = (event_sentinel,)
+
+ for i in range(1, 3):
+ with self.subTest('Loop %d/2' % i):
+ self.loop.call_soon(self.loop.stop)
+ self.loop.run_forever()
+ self.assertEqual(callcount, 1)
+
+ def test_run_once(self):
+ # Simple test for test_utils.run_once(). It may seem strange
+ # to have a test for this (the function isn't even used!) but
+ # it's a de-factor standard API for library tests. This tests
+ # the idiom: loop.call_soon(loop.stop); loop.run_forever().
+ count = 0
+
+ def callback():
+ nonlocal count
+ count += 1
+
+ self.loop._process_events = mock.Mock()
+ self.loop.call_soon(callback)
+ test_utils.run_once(self.loop)
+ self.assertEqual(count, 1)
+
+ def test_run_forever_pre_stopped(self):
+ # Test that the old idiom for pre-stopping the loop works.
+ self.loop._process_events = mock.Mock()
+ self.loop.stop()
+ self.loop.run_forever()
+ self.loop._selector.select.assert_called_once_with(0)
+
class MyProto(asyncio.Protocol):
done = None