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    Alive = 0,
8    Unregistered,
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::Unregistered), 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        if let State::Alive = self.state.get() {
36            self.val.get()
37        } else {
38            unsafe { self.get_or_init_slow() }
39        }
40    }
41
42    #[cold]
43    unsafe fn get_or_init_slow(&self) -> *const T {
44        match self.state.get() {
45            State::Unregistered => {}
46            State::Alive => return self.val.get(),
47            State::Destroyed => return ptr::null(),
48        }
49
50        // Register the destructor.
51
52        // SAFETY:
53        // The caller guarantees that `self` will be valid until thread destruction.
54        unsafe {
55            destructors::register(ptr::from_ref(self).cast_mut().cast(), destroy::<T>);
56        }
57
58        self.state.set(State::Alive);
59        self.val.get()
60    }
61}
62
63/// Transition an `Alive` TLS variable into the `Destroyed` state, dropping its
64/// value.
65///
66/// # Safety
67/// * Must only be called at thread destruction.
68/// * `ptr` must point to an instance of `Storage` with `Alive` state and be
69///   valid for accessing that instance.
70unsafe extern "C" fn destroy<T>(ptr: *mut u8) {
71    // Print a nice abort message if a panic occurs.
72    abort_on_dtor_unwind(|| {
73        let storage = unsafe { &*(ptr as *const Storage<T>) };
74        // Update the state before running the destructor as it may attempt to
75        // access the variable.
76        storage.state.set(State::Destroyed);
77        unsafe {
78            drop_in_place(storage.val.get());
79        }
80    })
81}
std/sys/thread_local/native/eager.rs

std/sys/thread_local/native/
eager.rs
