1 // SPDX-License-Identifier: GPL-2.0
3 //! A condition variable.
5 //! This module allows Rust code to use the kernel's [`struct wait_queue_head`] as a condition
8 use super::{lock::Backend, lock::Guard, LockClassKey};
14 task::{MAX_SCHEDULE_TIMEOUT, TASK_INTERRUPTIBLE, TASK_NORMAL, TASK_UNINTERRUPTIBLE},
18 use core::ffi::{c_int, c_long};
19 use core::marker::PhantomPinned;
23 /// Creates a [`CondVar`] initialiser with the given name and a newly-created lock class.
25 macro_rules! new_condvar {
26 ($($name:literal)?) => {
27 $crate::sync::CondVar::new($crate::optional_name!($($name)?), $crate::static_lock_class!())
32 /// A conditional variable.
34 /// Exposes the kernel's [`struct wait_queue_head`] as a condition variable. It allows the caller to
35 /// atomically release the given lock and go to sleep. It reacquires the lock when it wakes up. And
36 /// it wakes up when notified by another thread (via [`CondVar::notify_one`] or
37 /// [`CondVar::notify_all`]) or because the thread received a signal. It may also wake up
40 /// Instances of [`CondVar`] need a lock class and to be pinned. The recommended way to create such
41 /// instances is with the [`pin_init`](crate::pin_init) and [`new_condvar`] macros.
45 /// The following is an example of using a condvar with a mutex:
48 /// use kernel::sync::{new_condvar, new_mutex, CondVar, Mutex};
51 /// pub struct Example {
53 /// value: Mutex<u32>,
56 /// value_changed: CondVar,
59 /// /// Waits for `e.value` to become `v`.
60 /// fn wait_for_value(e: &Example, v: u32) {
61 /// let mut guard = e.value.lock();
62 /// while *guard != v {
63 /// e.value_changed.wait(&mut guard);
67 /// /// Increments `e.value` and notifies all potential waiters.
68 /// fn increment(e: &Example) {
69 /// *e.value.lock() += 1;
70 /// e.value_changed.notify_all();
73 /// /// Allocates a new boxed `Example`.
74 /// fn new_example() -> Result<Pin<Box<Example>>> {
75 /// Box::pin_init(pin_init!(Example {
76 /// value <- new_mutex!(0),
77 /// value_changed <- new_condvar!(),
82 /// [`struct wait_queue_head`]: srctree/include/linux/wait.h
86 pub(crate) wait_queue_head: Opaque<bindings::wait_queue_head>,
88 /// A condvar needs to be pinned because it contains a [`struct list_head`] that is
89 /// self-referential, so it cannot be safely moved once it is initialised.
91 /// [`struct list_head`]: srctree/include/linux/types.h
96 // SAFETY: `CondVar` only uses a `struct wait_queue_head`, which is safe to use on any thread.
97 #[allow(clippy::non_send_fields_in_send_ty)]
98 unsafe impl Send for CondVar {}
100 // SAFETY: `CondVar` only uses a `struct wait_queue_head`, which is safe to use on multiple threads
102 unsafe impl Sync for CondVar {}
105 /// Constructs a new condvar initialiser.
106 pub fn new(name: &'static CStr, key: &'static LockClassKey) -> impl PinInit<Self> {
109 // SAFETY: `slot` is valid while the closure is called and both `name` and `key` have
110 // static lifetimes so they live indefinitely.
111 wait_queue_head <- Opaque::ffi_init(|slot| unsafe {
112 bindings::__init_waitqueue_head(slot, name.as_char_ptr(), key.as_ptr())
117 fn wait_internal<T: ?Sized, B: Backend>(
120 guard: &mut Guard<'_, T, B>,
121 timeout_in_jiffies: c_long,
123 let wait = Opaque::<bindings::wait_queue_entry>::uninit();
125 // SAFETY: `wait` points to valid memory.
126 unsafe { bindings::init_wait(wait.get()) };
128 // SAFETY: Both `wait` and `wait_queue_head` point to valid memory.
130 bindings::prepare_to_wait_exclusive(self.wait_queue_head.get(), wait.get(), wait_state)
133 // SAFETY: Switches to another thread. The timeout can be any number.
134 let ret = guard.do_unlocked(|| unsafe { bindings::schedule_timeout(timeout_in_jiffies) });
136 // SAFETY: Both `wait` and `wait_queue_head` point to valid memory.
137 unsafe { bindings::finish_wait(self.wait_queue_head.get(), wait.get()) };
142 /// Releases the lock and waits for a notification in uninterruptible mode.
144 /// Atomically releases the given lock (whose ownership is proven by the guard) and puts the
145 /// thread to sleep, reacquiring the lock on wake up. It wakes up when notified by
146 /// [`CondVar::notify_one`] or [`CondVar::notify_all`]. Note that it may also wake up
148 pub fn wait<T: ?Sized, B: Backend>(&self, guard: &mut Guard<'_, T, B>) {
149 self.wait_internal(TASK_UNINTERRUPTIBLE, guard, MAX_SCHEDULE_TIMEOUT);
152 /// Releases the lock and waits for a notification in interruptible mode.
154 /// Similar to [`CondVar::wait`], except that the wait is interruptible. That is, the thread may
155 /// wake up due to signals. It may also wake up spuriously.
157 /// Returns whether there is a signal pending.
158 #[must_use = "wait_interruptible returns if a signal is pending, so the caller must check the return value"]
159 pub fn wait_interruptible<T: ?Sized, B: Backend>(&self, guard: &mut Guard<'_, T, B>) -> bool {
160 self.wait_internal(TASK_INTERRUPTIBLE, guard, MAX_SCHEDULE_TIMEOUT);
161 crate::current!().signal_pending()
164 /// Releases the lock and waits for a notification in interruptible mode.
166 /// Atomically releases the given lock (whose ownership is proven by the guard) and puts the
167 /// thread to sleep. It wakes up when notified by [`CondVar::notify_one`] or
168 /// [`CondVar::notify_all`], or when a timeout occurs, or when the thread receives a signal.
169 #[must_use = "wait_interruptible_timeout returns if a signal is pending, so the caller must check the return value"]
170 pub fn wait_interruptible_timeout<T: ?Sized, B: Backend>(
172 guard: &mut Guard<'_, T, B>,
174 ) -> CondVarTimeoutResult {
175 let jiffies = jiffies.try_into().unwrap_or(MAX_SCHEDULE_TIMEOUT);
176 let res = self.wait_internal(TASK_INTERRUPTIBLE, guard, jiffies);
178 match (res as Jiffies, crate::current!().signal_pending()) {
179 (jiffies, true) => CondVarTimeoutResult::Signal { jiffies },
180 (0, false) => CondVarTimeoutResult::Timeout,
181 (jiffies, false) => CondVarTimeoutResult::Woken { jiffies },
185 /// Calls the kernel function to notify the appropriate number of threads.
186 fn notify(&self, count: c_int) {
187 // SAFETY: `wait_queue_head` points to valid memory.
190 self.wait_queue_head.get(),
198 /// Calls the kernel function to notify one thread synchronously.
200 /// This method behaves like `notify_one`, except that it hints to the scheduler that the
201 /// current thread is about to go to sleep, so it should schedule the target thread on the same
203 pub fn notify_sync(&self) {
204 // SAFETY: `wait_queue_head` points to valid memory.
205 unsafe { bindings::__wake_up_sync(self.wait_queue_head.get(), TASK_NORMAL) };
208 /// Wakes a single waiter up, if any.
210 /// This is not 'sticky' in the sense that if no thread is waiting, the notification is lost
211 /// completely (as opposed to automatically waking up the next waiter).
212 pub fn notify_one(&self) {
216 /// Wakes all waiters up, if any.
218 /// This is not 'sticky' in the sense that if no thread is waiting, the notification is lost
219 /// completely (as opposed to automatically waking up the next waiter).
220 pub fn notify_all(&self) {
225 /// The return type of `wait_timeout`.
226 pub enum CondVarTimeoutResult {
227 /// The timeout was reached.
229 /// Somebody woke us up.
231 /// Remaining sleep duration.
234 /// A signal occurred.
236 /// Remaining sleep duration.