[DragonFlyBSD - Bug #3307] select() not working as expect when a pipe is closed

bugtracker-admin at leaf.dragonflybsd.org bugtracker-admin at leaf.dragonflybsd.org
Tue Dec 28 13:30:32 PST 2021

Issue #3307 has been updated by tmunro.

Hi again, will the fix be MFC'd to the 6.0 branch?  Thanks,

Bug #3307: select() not working as expect when a pipe is closed

* Author: tmunro
* Status: Resolved
* Priority: High
* Target version: 6.0
* Start date: 2021-11-19
When a the write end of a pipe is in the writefds set of a call to select(), and the read end is closed, I think select() should report the descriptor as writable (because writing would produce EPIPE or SIGPIPE), but it does not.  We suspect this changed, and we noticed the change in the PostgreSQL build farm after upgrading an ancient Dragonfly build machine to the current release.  In our real usage, this causes Perl IPC::Run in our test harness to hang, but here's a minimal repro in C:


(Please disregard the discussion of kqueue problems on ancient macOS, which turned out to be a separate problem, completely unrelated).

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