1 use crate::runtime::task::{Header, RawTask, Schedule};
2
3 use std::marker::PhantomData;
4 use std::mem::ManuallyDrop;
5 use std::ops;
6 use std::ptr::NonNull;
7 use std::task::{RawWaker, RawWakerVTable, Waker};
8
9 pub(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.
waker_ref<S>(header: &NonNull<Header>) -> WakerRef<'_, S> where S: Schedule,16 pub(super) fn waker_ref<S>(header: &NonNull<Header>) -> WakerRef<'_, S>
17 where
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
36 impl<S> ops::Deref for WakerRef<'_, S> {
37 type Target = Waker;
38
deref(&self) -> &Waker39 fn deref(&self) -> &Waker {
40 &self.waker
41 }
42 }
43
44 cfg_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 = $op,
51 task.id = id.into_u64(),
52 );
53 }
54 }
55 }
56 }
57
58 cfg_not_trace! {
59 macro_rules! trace {
60 ($header:expr, $op:expr) => {
61 // noop
62 let _ = &$header;
63 }
64 }
65 }
66
clone_waker(ptr: *const ()) -> RawWaker67 unsafe 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
drop_waker(ptr: *const ())74 unsafe 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
wake_by_val(ptr: *const ())81 unsafe 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
wake_by_ref(ptr: *const ())89 unsafe 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
96 static WAKER_VTABLE: RawWakerVTable =
97 RawWakerVTable::new(clone_waker, wake_by_val, wake_by_ref, drop_waker);
98
raw_waker(header: NonNull<Header>) -> RawWaker99 fn raw_waker(header: NonNull<Header>) -> RawWaker {
100 let ptr = header.as_ptr() as *const ();
101 RawWaker::new(ptr, &WAKER_VTABLE)
102 }
103