gh-124309: fix staggered race on eager tasks (#124847)

This patch is entirely by Thomas and Peter

Co-authored-by: Thomas Grainger <tagrain@gmail.com>
Co-authored-by: Peter Bierma <zintensitydev@gmail.com>

2 files changed, 73 insertions, 0 deletions

diff --git a/Lib/test/test_asyncio/test_eager_task_factory.py b/Lib/test/test_asyncio/test_eager_task_factory.py
index 0777f39..31d2a00 100644
--- a/Lib/test/test_asyncio/test_eager_task_factory.py
+++ b/Lib/test/test_asyncio/test_eager_task_factory.py
@@ -213,6 +213,52 @@ class EagerTaskFactoryLoopTests:
 
         self.run_coro(run())
 
+    def test_staggered_race_with_eager_tasks(self):
+        # See https://github.com/python/cpython/issues/124309
+
+        async def fail():
+            await asyncio.sleep(0)
+            raise ValueError("no good")
+
+        async def run():
+            winner, index, excs = await asyncio.staggered.staggered_race(
+                [
+                    lambda: asyncio.sleep(2, result="sleep2"),
+                    lambda: asyncio.sleep(1, result="sleep1"),
+                    lambda: fail()
+                ],
+                delay=0.25
+            )
+            self.assertEqual(winner, 'sleep1')
+            self.assertEqual(index, 1)
+            self.assertIsNone(excs[index])
+            self.assertIsInstance(excs[0], asyncio.CancelledError)
+            self.assertIsInstance(excs[2], ValueError)
+
+        self.run_coro(run())
+
+    def test_staggered_race_with_eager_tasks_no_delay(self):
+        # See https://github.com/python/cpython/issues/124309
+        async def fail():
+            raise ValueError("no good")
+
+        async def run():
+            winner, index, excs = await asyncio.staggered.staggered_race(
+                [
+                    lambda: fail(),
+                    lambda: asyncio.sleep(1, result="sleep1"),
+                    lambda: asyncio.sleep(0, result="sleep0"),
+                ],
+                delay=None
+            )
+            self.assertEqual(winner, 'sleep1')
+            self.assertEqual(index, 1)
+            self.assertIsNone(excs[index])
+            self.assertIsInstance(excs[0], ValueError)
+            self.assertEqual(len(excs), 2)
+
+        self.run_coro(run())
+
 
 class PyEagerTaskFactoryLoopTests(EagerTaskFactoryLoopTests, test_utils.TestCase):
     Task = tasks._PyTask
diff --git a/Lib/test/test_asyncio/test_staggered.py b/Lib/test/test_asyncio/test_staggered.py
index e6e32f7..74941f7 100644
--- a/Lib/test/test_asyncio/test_staggered.py
+++ b/Lib/test/test_asyncio/test_staggered.py
@@ -95,3 +95,30 @@ class StaggeredTests(unittest.IsolatedAsyncioTestCase):
         self.assertEqual(len(excs), 2)
         self.assertIsInstance(excs[0], ValueError)
         self.assertIsInstance(excs[1], ValueError)
+
+
+    async def test_multiple_winners(self):
+        event = asyncio.Event()
+
+        async def coro(index):
+            await event.wait()
+            return index
+
+        async def do_set():
+            event.set()
+            await asyncio.Event().wait()
+
+        winner, index, excs = await staggered_race(
+            [
+                lambda: coro(0),
+                lambda: coro(1),
+                do_set,
+            ],
+            delay=0.1,
+        )
+        self.assertIs(winner, 0)
+        self.assertIs(index, 0)
+        self.assertEqual(len(excs), 3)
+        self.assertIsNone(excs[0], None)
+        self.assertIsInstance(excs[1], asyncio.CancelledError)
+        self.assertIsInstance(excs[2], asyncio.CancelledError)