[3.14] gh-154366: Fix test_asyncio.test_sendfile timing out on DragonFly BSD (GH-154367) (GH-154372)

https://github.com/python/cpython/commit/1f0cbea50b3eb1d57ea2328ed1101c4ec82c1f9e
commit: 1f0cbea50b3eb1d57ea2328ed1101c4ec82c1f9e
branch: 3.14
author: Miss Islington (bot) <[email protected]>
committer: serhiy-storchaka <[email protected]>
date: 2026-07-21T15:31:47Z
summary:

[3.14] gh-154366: Fix test_asyncio.test_sendfile timing out on DragonFly BSD (GH-154367) (GH-154372)

A 4 KiB receive buffer makes DragonFly defer every window update to the
delayed ACK timer, so each buffer worth of data costs 100 ms.  Use a
larger socket buffer there; it is still small enough to pause the
protocol long before all data is sent.
(cherry picked from commit a6e1b836ec5055cbc8be477ca0c2df0cc12b8cb5)

Co-authored-by: Serhiy Storchaka <[email protected]>
Co-authored-by: Claude Opus 4.8 <[email protected]>

files:
M Lib/test/test_asyncio/test_sendfile.py

diff --git a/Lib/test/test_asyncio/test_sendfile.py b/Lib/test/test_asyncio/test_sendfile.py
index 7afd7de3bb936e6..bdc3aa604a158f3 100644
--- a/Lib/test/test_asyncio/test_sendfile.py
+++ b/Lib/test/test_asyncio/test_sendfile.py
@@ -98,7 +98,12 @@ class SendfileBase:
     # 64 KiB page configuration.
     DATA = b"x" * (1024 * 17 * 64 + 1)
     # Reduce socket buffer size to test on relative small data sets.
-    BUF_SIZE = 4 * 1024   # 4 KiB
+    if sys.platform.startswith('dragonfly'):
+        # A smaller buffer makes every window update wait 100 ms for the
+        # delayed ACK timer.
+        BUF_SIZE = 32 * 1024  # 32 KiB
+    else:
+        BUF_SIZE = 4 * 1024   # 4 KiB
 
     def create_event_loop(self):
         raise NotImplementedError

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