add an async read method to EventFD

Adding an async write does not work for values larger than 1, because
the fd becomes writable once a value of 1 can be written, but a larger
value might still cause EAGAIN putting us into a busy loop. Hitting the
limit with writing ones is implausible, so async code can just use the
synchronous write method.

1 files changed, 15 insertions, 0 deletions

diff --git a/tests/test_simple.py b/tests/test_simple.py
index 960bf02..5889e25 100644
--- a/tests/test_simple.py
+++ b/tests/test_simple.py
@@ -1,6 +1,7 @@
 # Copyright 2024 Helmut Grohne <helmut@subdivi.de>
 # SPDX-License-Identifier: GPL-3
 
+import asyncio
 import functools
 import os
 import pathlib
@@ -48,6 +49,20 @@ class IDAllocationTest(unittest.TestCase):
         self.assertIn(alloc.allocate(3), (1, 2))
 
 
+class EventFDTest(unittest.IsolatedAsyncioTestCase):
+    async def test_async(self) -> None:
+        efd = linuxnamespaces.EventFD(1, linuxnamespaces.EventFDFlags.NONBLOCK)
+        fut = efd.aread()
+        await asyncio.sleep(0.000001)  # Let the loop run
+        self.assertTrue(fut.done())
+        self.assertEqual(await fut, 1)
+        fut = efd.aread()
+        await asyncio.sleep(0.000001)  # Let the loop run
+        self.assertFalse(fut.done())
+        efd.write()
+        self.assertEqual(await fut, 1)
+
+
 class UnshareTest(unittest.TestCase):
     @pytest.mark.forked
     def test_unshare_user(self) -> None: