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<a href="https://gitlab.rtems.org/junkes">Heinz Junkes</a> created an issue: <a href="https://gitlab.rtems.org/rtems/rtos/rtems/-/issues/5623">#5623</a>
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<h2 id="user-content-summary" dir="auto" style="margin-top: 0; margin-bottom: 10px;" align="initial">Summary<a href="#summary" aria-label="Link to heading 'Summary'" data-heading-content="Summary" class="anchor" style="margin-top: 0;"></a>
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<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">Location: cpukit/libfs/src/pipe/{pipe.c,fifo.c}</p>
<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">Root cause: pipe() clears LIBIO_FLAGS_NO_DELAY on the read fd after open (pipe.c:89).</p>
<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">pipe_ioctl (fifo.c:435) only implements FIONREAD, with no FIONBIO case and no fcntl(F_SETFL) passthrough that updates iop flags</p>
<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">Effect: pipe_read's LIBIO_NODELAY(iop) check (fifo.c:309) is dead code for any fd obtained via pipe()
[reads on an empty pipe always block, regardless of subsequent non-blocking calls]</p>
<h2 id="user-content-steps-to-reproduce" dir="auto" style="margin-top: 20px; margin-bottom: 10px;" align="initial">Steps to reproduce<a href="#steps-to-reproduce" aria-label="Link to heading 'Steps to reproduce'" data-heading-content="Steps to reproduce" class="anchor" style="margin-top: 0;"></a>
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<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">breaks any library relying on the standard non-blocking-pipe self-pipe/notification pattern (libevent, EPICS extension PVXS, on RTEMS 7 ( origin/main )</p>
<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">I'm currently working on libevent (EPICS PVXS):</p>
<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">evutil_make_internal_pipe_ in bundled libevent used pipe() + O_NONBLOCK for cross-thread event loop notification. On RTEMS libbsd, O_NONBLOCK on pipe file descriptors is unreliable — reads block instead of returning EAGAIN. This caused evthread_notify_drain_default to block holding the libevent internal lock, deadlocking event_base_loop in all evbase instances, preventing acceptor_loop.call() from ever completing.</p>
<p dir="auto" style="color: #3a383f; margin: 0;" align="initial">Fix: Add && !defined(<strong style="font-weight: 600; margin-top: 0;">rtems</strong>) to the #if defined(EVENT__HAVE_PIPE) guard in bundle/libevent/evutil.c, forcing libevent to use socketpair(AF_UNIX, SOCK_STREAM) instead on RTEMS — which works correctly.</p>
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