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)]
13#[repr(C)]
14pub struct Storage<T> {
15    // This field must be first, for correctness of `#[rustc_align_static]`
16    val: UnsafeCell<T>,
17    state: Cell<State>,
18}
19
20impl<T> Storage<T> {
21    pub const fn new(val: T) -> Storage<T> {
22        Storage { state: Cell::new(State::Initial), val: UnsafeCell::new(val) }
23    }
24
25    /// Gets a pointer to the TLS value. If the TLS variable has been destroyed,
26    /// a null pointer is returned.
27    ///
28    /// The resulting pointer may not be used after thread destruction has
29    /// occurred.
30    ///
31    /// # Safety
32    /// The `self` reference must remain valid until the TLS destructor is run.
33    #[inline]
34    pub unsafe fn get(&self) -> *const T {
35        match self.state.get() {
36            State::Alive => self.val.get(),
37            State::Destroyed => ptr::null(),
38            State::Initial => unsafe { self.initialize() },
39        }
40    }
41
42    #[cold]
43    unsafe fn initialize(&self) -> *const T {
44        // Register the destructor
45
46        // SAFETY:
47        // The caller guarantees that `self` will be valid until thread destruction.
48        unsafe {
49            destructors::register(ptr::from_ref(self).cast_mut().cast(), destroy::<T>);
50        }
51
52        self.state.set(State::Alive);
53        self.val.get()
54    }
55}
56
57/// Transition an `Alive` TLS variable into the `Destroyed` state, dropping its
58/// value.
59///
60/// # Safety
61/// * Must only be called at thread destruction.
62/// * `ptr` must point to an instance of `Storage` with `Alive` state and be
63///   valid for accessing that instance.
64unsafe extern "C" fn destroy<T>(ptr: *mut u8) {
65    // Print a nice abort message if a panic occurs.
66    abort_on_dtor_unwind(|| {
67        let storage = unsafe { &*(ptr as *const Storage<T>) };
68        // Update the state before running the destructor as it may attempt to
69        // access the variable.
70        storage.state.set(State::Destroyed);
71        unsafe {
72            drop_in_place(storage.val.get());
73        }
74    })
75}
std/sys/thread_local/native/eager.rs

std/sys/thread_local/native/
eager.rs
