gh-145030: Fix asyncio write pipe transport for named FIFOs on macOS#154222
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kumaraditya303 merged 4 commits intoJul 24, 2026
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…macOS On macOS the write end of a named FIFO polls as readable whenever unread data sits in the FIFO, so the reader trick used to detect the peer closing misfired and closed the transport. The trick also cannot detect a genuine hangup there: closing the read end delivers no event and kqueue's EV_EOF tracks writers, not readers. Skip registering the reader for named FIFOs on macOS, like the existing AIX carve-out; a closed peer is still detected on the next write via EPIPE. Anonymous os.pipe() pipes (st_nlink == 0) keep the current behaviour.
bhuvi27
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1st1,
asvetlov,
kumaraditya303 and
willingc
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July 20, 2026 07:09
sys.platform is "ios" (etc.) on Apple mobile, not "darwin", so the named-FIFO carve-out never applied there and the new regression test failed on the iOS CI job. Match all Apple platforms.
Rename the carve-out variable and wording back to macOS; keep the platform set covering ios/tvos/watchos so the same xnu FIFO behaviour is handled there.
Rename is_named_fifo_on_macos to is_named_fifo_on_apple to match the Apple platform set, and assert st_nlink != 0 in the named FIFO test.
kumaraditya303
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Jul 24, 2026
kumaraditya303
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needs backport to 3.13
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Thanks @bhuvi27 for the PR, and @kumaraditya303 for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13. |
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Thanks @bhuvi27 for the PR, and @kumaraditya303 for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14. |
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Thanks @bhuvi27 for the PR, and @kumaraditya303 for merging it 🌮🎉.. I'm working now to backport this PR to: 3.15. |
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GH-154611 is a backport of this pull request to the 3.13 branch. |
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GH-154612 is a backport of this pull request to the 3.14 branch. |
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GH-154613 is a backport of this pull request to the 3.15 branch. |
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Fixes #145030
On macOS, the write end of a named FIFO polls as readable whenever unread data sits in the FIFO (the kernel does not check the fd's access mode,unlike Linux), so the "reader trick" _UnixWritePipeTransport uses to detect
the peer closing misfired and closed the transport, making the next drain() raise ConnectionResetError. The trick also cannot detect a genuine hangup for named FIFOs on macOS: closing the read end produces no event, and
kqueue's EV_EOF tracks writers rather than readers.
Skip registering the reader for named FIFOs on macOS, matching the existing AIX carve-out; a closed peer is still detected on the next write via EPIPE. Anonymous os.pipe() pipes are unaffected (st_nlink == 0) and keep the
current behaviour. Adds a regression test that keeps unread data in a FIFO while iterating the loop, which fails without the fix on macOS.