tokio/runtime/task/
waker.rs

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1use crate::runtime::task::{Header, RawTask, Schedule};
2
3use std::marker::PhantomData;
4use std::mem::ManuallyDrop;
5use std::ops;
6use std::ptr::NonNull;
7use std::task::{RawWaker, RawWakerVTable, Waker};
8
9pub(super) struct WakerRef<'a, S: 'static> {
10    waker: ManuallyDrop<Waker>,
11    _p: PhantomData<(&'a Header, S)>,
12}
13
14/// Returns a `WakerRef` which avoids having to preemptively increase the
15/// refcount if there is no need to do so.
16pub(super) fn waker_ref<S>(header: &NonNull<Header>) -> WakerRef<'_, S>
17where
18    S: Schedule,
19{
20    // `Waker::will_wake` uses the VTABLE pointer as part of the check. This
21    // means that `will_wake` will always return false when using the current
22    // task's waker. (discussion at rust-lang/rust#66281).
23    //
24    // To fix this, we use a single vtable. Since we pass in a reference at this
25    // point and not an *owned* waker, we must ensure that `drop` is never
26    // called on this waker instance. This is done by wrapping it with
27    // `ManuallyDrop` and then never calling drop.
28    let waker = unsafe { ManuallyDrop::new(Waker::from_raw(raw_waker(*header))) };
29
30    WakerRef {
31        waker,
32        _p: PhantomData,
33    }
34}
35
36impl<S> ops::Deref for WakerRef<'_, S> {
37    type Target = Waker;
38
39    fn deref(&self) -> &Waker {
40        &self.waker
41    }
42}
43
44cfg_trace! {
45    macro_rules! trace {
46        ($header:expr, $op:expr) => {
47            if let Some(id) = Header::get_tracing_id(&$header) {
48                tracing::trace!(
49                    target: "tokio::task::waker",
50                    op = $op,
51                    task.id = id.into_u64(),
52                );
53            }
54        }
55    }
56}
57
58cfg_not_trace! {
59    macro_rules! trace {
60        ($header:expr, $op:expr) => {
61            // noop
62            let _ = &$header;
63        }
64    }
65}
66
67unsafe fn clone_waker(ptr: *const ()) -> RawWaker {
68    let header = NonNull::new_unchecked(ptr as *mut Header);
69    trace!(header, "waker.clone");
70    header.as_ref().state.ref_inc();
71    raw_waker(header)
72}
73
74unsafe fn drop_waker(ptr: *const ()) {
75    let ptr = NonNull::new_unchecked(ptr as *mut Header);
76    trace!(ptr, "waker.drop");
77    let raw = RawTask::from_raw(ptr);
78    raw.drop_reference();
79}
80
81unsafe fn wake_by_val(ptr: *const ()) {
82    let ptr = NonNull::new_unchecked(ptr as *mut Header);
83    trace!(ptr, "waker.wake");
84    let raw = RawTask::from_raw(ptr);
85    raw.wake_by_val();
86}
87
88// Wake without consuming the waker
89unsafe fn wake_by_ref(ptr: *const ()) {
90    let ptr = NonNull::new_unchecked(ptr as *mut Header);
91    trace!(ptr, "waker.wake_by_ref");
92    let raw = RawTask::from_raw(ptr);
93    raw.wake_by_ref();
94}
95
96static WAKER_VTABLE: RawWakerVTable =
97    RawWakerVTable::new(clone_waker, wake_by_val, wake_by_ref, drop_waker);
98
99fn raw_waker(header: NonNull<Header>) -> RawWaker {
100    let ptr = header.as_ptr() as *const ();
101    RawWaker::new(ptr, &WAKER_VTABLE)
102}
tokio/runtime/task/waker.rs

tokio/runtime/task/
waker.rs
