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<a href="https://gitlab.rtems.org/aptacc2421">Xinhong Hu</a>
commented on a
<a href="https://gitlab.rtems.org/rtems/rtos/rtems/-/issues/3791#note_143086">discussion</a>:
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<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">Hi <a href="https://gitlab.rtems.org/joel" title="Joel Sherrill" class="gfm gfm-project_member js-user-link" data-user="7" data-original="@joel" data-container="body" data-placement="top" data-reference-type="user" style="color: #284779; background-color: #cbe2f9; border-radius: .25rem; margin-top: 0; padding: 0 2px;">@joel</a> , <a href="https://gitlab.rtems.org/gedare" title="Gedare Bloom" class="gfm gfm-project_member js-user-link" data-user="8" data-original="@gedare" data-container="body" data-placement="top" data-reference-type="user" style="color: #284779; background-color: #cbe2f9; border-radius: .25rem; padding: 0 2px;">@gedare</a></p>
<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">Thank you for the thoughtful discussion. I've been prototyping the per-instance approach Joel suggested: adding an RTEMS-specific field <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; margin-top: 0; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">mq_ispriority</code> to struct <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">mq_attr</code>. This allows each queue to independently choose FIFO or priority wake-up order, with a default of FIFO to maintain backward compatibility. My tests on RTEMS 7 confirm that setting <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">mq_ispriority = 1</code> correctly wakes a higher-priority thread that blocks later.</p>
<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">Regarding Gedare's point about application configuration: I think per-instance control already gives applications the ability to configure individual queues. However, to also support system-wide defaults, we could add a configuration macro in <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; margin-top: 0; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;"><rtems/confdefs.h></code> (e.g., <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">CONFIGURE_POSIX_MESSAGE_QUEUE_DEFAULT_DISCIPLINE</code>) that sets the initial value of <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">mq_ispriority</code> for queues created with a NULL attribute. This would allow integrators to change the global default without modifying each <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">mq_open</code> call, while still permitting per-queue overrides.</p>
<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">For my GSoC project, I propose to implement both the per-instance field and the global configuration option. The core deliverables would be:</p>
<ol dir="auto" style="text-align: initial; margin: 0 0 1rem; padding: 0;">
<li style="margin-top: 0; line-height: 1.6em; margin-left: 25px; padding-left: 3px;">Extend struct <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; margin-top: 0; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; white-space: pre-wrap; overflow-wrap: break-word; word-break: keep-all; padding: 0.125rem 0.25rem;">mq_attr</code> with <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; white-space: pre-wrap; overflow-wrap: break-word; word-break: keep-all; padding: 0.125rem 0.25rem;">mq_ispriority</code> (guarded by <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; white-space: pre-wrap; overflow-wrap: break-word; word-break: keep-all; padding: 0.125rem 0.25rem;">#ifdef __RTEMS__</code>).</li>
<li style="line-height: 1.6em; margin-left: 25px; padding-left: 3px;">Modify <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; margin-top: 0; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; white-space: pre-wrap; overflow-wrap: break-word; word-break: keep-all; padding: 0.125rem 0.25rem;">mq_open()</code> to interpret this field and pass the discipline to the core message queue.</li>
<li style="line-height: 1.6em; margin-left: 25px; padding-left: 3px;">Add a configuration macro in <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; margin-top: 0; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; white-space: pre-wrap; overflow-wrap: break-word; word-break: keep-all; padding: 0.125rem 0.25rem;"><rtems/confdefs.h></code> to set the default discipline.</li>
<li style="line-height: 1.6em; margin-left: 25px; padding-left: 3px;">Provide comprehensive tests and documentation.</li>
</ol>
<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">I believe this scope is manageable within the GSoC timeframe and fully resolves <a href="https://gitlab.rtems.org/rtems/rtos/rtems/-/issues/3791" title="POSIX Message Queue thread release order is not priority based" class="gfm gfm-issue" data-original="#3791" data-link="false" data-link-reference="false" data-issue="26273" data-project="26" data-iid="3791" data-namespace-path="rtems/rtos/rtems" data-project-path="rtems/rtos/rtems" data-issue-type="issue" data-container="body" data-placement="top" data-reference-type="issue" style="margin-top: 0;">#3791</a> while offering flexibility for future needs. I'd appreciate your feedback on whether this plan aligns with your expectations. If you prefer a simpler approach (only per-instance or only global), I can adjust accordingly.</p>
<p dir="auto" style="color: #3a383f; margin: 0;" align="initial">Thank you for your guidance!</p>
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