std/sys/thread_local/native/
eager.rs

1use crate::cell::{Cell, UnsafeCell};
2use crate::ptr::{self, drop_in_place};
3use crate::sys::thread_local::{abort_on_dtor_unwind, destructors};
4
5#[derive(Clone, Copy)]
6enum State {
7    Initial,
8    Alive,
9    Destroyed,
10}
11
12#[allow(missing_debug_implementations)]
13pub struct Storage<T> {
14    state: Cell<State>,
15    val: UnsafeCell<T>,
16}
17
18impl<T> Storage<T> {
19    pub const fn new(val: T) -> Storage<T> {
20        Storage { state: Cell::new(State::Initial), val: UnsafeCell::new(val) }
21    }
22
23    /// Gets a pointer to the TLS value. If the TLS variable has been destroyed,
24    /// a null pointer is returned.
25    ///
26    /// The resulting pointer may not be used after thread destruction has
27    /// occurred.
28    ///
29    /// # Safety
30    /// The `self` reference must remain valid until the TLS destructor is run.
31    #[inline]
32    pub unsafe fn get(&self) -> *const T {
33        match self.state.get() {
34            State::Alive => self.val.get(),
35            State::Destroyed => ptr::null(),
36            State::Initial => unsafe { self.initialize() },
37        }
38    }
39
40    #[cold]
41    unsafe fn initialize(&self) -> *const T {
42        // Register the destructor
43
44        // SAFETY:
45        // The caller guarantees that `self` will be valid until thread destruction.
46        unsafe {
47            destructors::register(ptr::from_ref(self).cast_mut().cast(), destroy::<T>);
48        }
49
50        self.state.set(State::Alive);
51        self.val.get()
52    }
53}
54
55/// Transition an `Alive` TLS variable into the `Destroyed` state, dropping its
56/// value.
57///
58/// # Safety
59/// * Must only be called at thread destruction.
60/// * `ptr` must point to an instance of `Storage` with `Alive` state and be
61///   valid for accessing that instance.
62unsafe extern "C" fn destroy<T>(ptr: *mut u8) {
63    // Print a nice abort message if a panic occurs.
64    abort_on_dtor_unwind(|| {
65        let storage = unsafe { &*(ptr as *const Storage<T>) };
66        // Update the state before running the destructor as it may attempt to
67        // access the variable.
68        storage.state.set(State::Destroyed);
69        unsafe {
70            drop_in_place(storage.val.get());
71        }
72    })
73}
std/sys/thread_local/native/eager.rs

std/sys/thread_local/native/
eager.rs
