Date: Sun, 10 May 2020 07:22:40 +0000 From: bugzilla-noreply@freebsd.org To: bugs@FreeBSD.org Subject: [Bug 246350] kqueue fails to report pipe writable after the read end is closed Message-ID: <bug-246350-227@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D246350 Bug ID: 246350 Summary: kqueue fails to report pipe writable after the read end is closed Product: Base System Version: 12.1-RELEASE Hardware: Any OS: Any Status: New Severity: Affects Only Me Priority: --- Component: kern Assignee: bugs@FreeBSD.org Reporter: njs@pobox.com Attachment #214335 text/plain mime type: Created attachment 214335 --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=3D214335&action= =3Dedit fbsd-kqueue-pipe-bug-demo.py Consider the following sequence of events: 1. Call pipe() to open a pipe 2. Set the write side to non-blocking 3. Write into the write side until the pipe buffer is full and write() retu= rns EWOULDBLOCK 4. Use kqueue to register a wait for the write end to become writable again (EVFILT_WRITE) 5. Close the read end of the pipe At this point, I would expect that kqueue would return an event to report t= hat the pipe is "writable". The man page says it will ("The filter will set EV_= EOF when the reader disconnects"). On the same pipe, in this situation, select() reports that it's writable. On macOS, kqueue reports that it's writable. However, on FreeBSD 12, kqueue does *not* report any event in this situatio= n. I've attached a minimal Python script to demonstrate. Output from the script when running on macOS: ------------ filling pipe buffer select() says the write pipe is NOT writable closing read end of pipe select() says the write pipe is writable waiting for kqueue to report the write end is writable done! [<select.kevent ident=3D4 filter=3D-2 flags=3D0x8001 fflags=3D0x0 data=3D0x= 0 udata=3D0x0>] ------------ Output from the script when running on FreeBSD 12.1-RELEASE: ------------ filling pipe buffer select() says the write pipe is NOT writable closing read end of pipe select() says the write pipe is writable waiting for kqueue to report the write end is writable [...hangs forever...] ------------ --=20 You are receiving this mail because: You are the assignee for the bug.=
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