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[EXPERIMENTAL]sched/hrtimer: update hrtimer document

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Update the hrtimer documentation to describe the hrtimer state machine,
    which is introduced to handle safe cancellation and execution in SMP
    environments.

Signed-off-by: Chengdong Wang <wangchengdong@lixiang.com>
This commit is contained in:
wangchengdong
2026-01-06 12:24:09 +08:00
committed by GUIDINGLI
parent 1020bc74e8
commit 24651af90c
2 changed files with 17 additions and 4 deletions
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Documentation/reference/os/hrtimer_state_machine.png
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Documentation/reference/os/time_clock.rst
+17 -4
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@@ -675,14 +675,28 @@ The callback runs in the timer interrupt context, so only limited NuttX interfac
are available, such as ``mq_send()``, ``sigqueue()``, ``nxevent_post()``, or ``kill()``,
to communicate with tasks.
High-resolution timers (hrtimers) use a spinlock to protect internal timer data structures,
allowing them to be safely accessed from interrupt context. This design makes hrtimers
suitable for high-frequency timer operations.
However, in SMP systems, a potential issue arises when a user cancels a timer that is currently
executing: the timer instance may be freed prematurely while its callback is still running.
To address this problem, a state machine is introduced in the hrtimer implementation:
.. image:: hrtimer_state_machine.png
:alt: hrtimer state machine
Users may call ``hrtimer_cancel_sync()`` to synchronously cancel a timer and wait until the
timer becomes fully inactive. In contrast, ``hrtimer_cancel()`` is a non-blocking variant
that returns immediately without waiting for the timer to stop executing.
- :c:func:`hrtimer_init`
- :c:func:`hrtimer_cancel`
- :c:func:`hrtimer_cancel_sync`
- :c:func:`hrtimer_start`
- High-resolution Timer Callback
.. c:function:: void hrtimer_init(FAR hrtimer_t *hrtimer, hrtentry_t func, \
FAR void *arg)
.. c:function:: void hrtimer_init(FAR hrtimer_t *hrtimer, hrtentry_t func)
This function initializes a high-resolution timer instance.
Sets the expiration callback and its argument. The timer is
@@ -690,7 +704,6 @@ to communicate with tasks.
:param hrtimer: Pointer to hrtimer instance
:param func: Expiration callback function
:param arg: Callback argument
:return: None.
@@ -745,7 +758,7 @@ to communicate with tasks.
**POSIX Compatibility:** This is a NON-POSIX interface.
.. c:type:: void (*hrtentry_t)(FAR struct hrtimer_s *)
.. c:type:: uint64_t (*hrtimer_cb)(FAR hrtimer_t *hrtimer, uint64_t expired)
**High-resolution Timer Callback**: when a hrtimer expires,
the callback function with this type is called.