fix(cie): apply SCHED_DEADLINE immediately using SCHED_FLAG_RESET_ON_FORK

[atsushi421]

Description

Previously, SCHED_DEADLINE configurations were applied via a delayed, interactive workflow: the configurator waited for a user prompt ("Apply sched deadline?") before applying them. This was a workaround because SCHED_DEADLINE threads could not call fork(2)/clone(2) without triggering EAGAIN, which caused issues with nodes that spawn child threads at startup (e.g., EKF Localizer).

This PR eliminates the delayed application by setting SCHED_FLAG_RESET_ON_FORK in sched_attr.sched_flags for SCHED_DEADLINE threads. With this flag, children of SCHED_DEADLINE threads reset to SCHED_OTHER, allowing fork/clone to succeed. All scheduling policies, including SCHED_DEADLINE, are now applied immediately upon receiving callback group or non-ROS thread info.

Key changes:

• Set SCHED_FLAG_RESET_ON_FORK for SCHED_DEADLINE threads in issue_syscalls()
• Remove the deadline_configs_ vector and delayed application logic
• Remove exist_deadline_config() and apply_deadline_configs() methods; add has_cgroup() const
• Remove the interactive "Apply sched deadline?" prompt from main; show success message immediately
• Add RCLCPP_WARN logs when syscall application fails for a thread
• Update README to reflect the simplified workflow (no more delayed SCHED_DEADLINE step)

Related links

port from autowarefoundation/agnocast#1248

How was this PR tested?

Notes for reviewers

[Copilot]

Pull request overview

This PR removes the delayed/interactive application of SCHED_DEADLINE by setting SCHED_FLAG_RESET_ON_FORK, allowing fork(2)/clone(2) to succeed from SCHED_DEADLINE threads, and applies all scheduling policies immediately when thread info is received.

Changes:

• Apply SCHED_DEADLINE immediately by setting SCHED_FLAG_RESET_ON_FORK in the sched_setattr() path.
• Remove delayed SCHED_DEADLINE buffering/application APIs and simplify the main workflow.
• Update user-facing logs and README to reflect the simplified runtime flow.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
cie_thread_configurator/src/thread_configurator_node_main.cpp	Removes the interactive “Apply sched deadline?” step; only blocks for cgroup cleanup.
cie_thread_configurator/src/thread_configurator_node.cpp	Sets SCHED_FLAG_RESET_ON_FORK for SCHED_DEADLINE; removes delayed application list; adds warnings on syscall failure.
cie_thread_configurator/include/cie_thread_configurator/thread_configurator_node.hpp	Removes delayed-apply APIs/state; adds has_cgroup() const.
README.md	Removes delayed SCHED_DEADLINE workflow documentation and updates runtime instructions.

Comments suppressed due to low confidence (1)

cie_thread_configurator/src/thread_configurator_node.cpp:283

• sched_setattr() has historically required sched_flags to be 0 on some kernels (and the manpage still documents restrictions), so setting SCHED_FLAG_RESET_ON_FORK may cause sched_setattr to fail with EINVAL on those systems. Since this is intended as a compatibility improvement, consider a fallback path: try with SCHED_FLAG_RESET_ON_FORK, and if the syscall fails specifically due to unsupported flags, retry with sched_flags = 0 and emit a clear warning that RESET_ON_FORK is not supported (and that fork/clone from SCHED_DEADLINE threads may fail).

    struct sched_attr attr;
    memset(&attr, 0, sizeof(attr));
    attr.size = sizeof(attr);
    // SCHED_FLAG_RESET_ON_FORK lets the target thread still call
    // fork(2)/clone(2) after being placed under SCHED_DEADLINE; without it,
    // clone(2) returns EAGAIN. Children reset to SCHED_OTHER; each
    // callback-group thread that needs its own SCHED_DEADLINE gets it via its
    // own CallbackGroupInfo message.
    attr.sched_flags = SCHED_FLAG_RESET_ON_FORK;
    attr.sched_nice = 0;
    attr.sched_priority = 0;

    attr.sched_policy = SCHED_DEADLINE;
    attr.sched_runtime = config.runtime;
    attr.sched_period = config.period;
    attr.sched_deadline = config.deadline;

    if (sched_setattr(config.thread_id, &attr, 0) == -1) {
      RCLCPP_ERROR(
          this->get_logger(), "Failed to configure policy (id=%s, tid=%ld): %s",
          config.thread_str.c_str(), config.thread_id, strerror(errno));
      return false;

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.