1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
|
//! This module is full of hackery and dark magic.
//! Either spend a day fixing it and quietly submit a PR or don't mention it to anybody.
use core::cell::UnsafeCell;
use core::{mem, ptr};
pub const fn ptr_size_bits() -> usize {
mem::size_of::<usize>() * 8
}
pub fn map_in_place_2<T, U, F: FnOnce(U, T) -> T>((k, v): (U, &mut T), f: F) {
unsafe {
// # Safety
//
// If the closure panics, we must abort otherwise we could double drop `T`
let _promote_panic_to_abort = AbortOnPanic;
ptr::write(v, f(k, ptr::read(v)));
}
}
/// # Safety
///
/// Requires that you ensure the reference does not become invalid.
/// The object has to outlive the reference.
pub unsafe fn change_lifetime_const<'a, 'b, T>(x: &'a T) -> &'b T {
&*(x as *const T)
}
/// # Safety
///
/// Requires that you ensure the reference does not become invalid.
/// The object has to outlive the reference.
pub unsafe fn change_lifetime_mut<'a, 'b, T>(x: &'a mut T) -> &'b mut T {
&mut *(x as *mut T)
}
/// A simple wrapper around `T`
///
/// This is to prevent UB when using `HashMap::get_key_value`, because
/// `HashMap` doesn't expose an api to get the key and value, where
/// the value is a `&mut T`.
///
/// See [#10](https://github.com/xacrimon/dashmap/issues/10) for details
///
/// This type is meant to be an implementation detail, but must be exposed due to the `Dashmap::shards`
#[repr(transparent)]
pub struct SharedValue<T> {
value: UnsafeCell<T>,
}
impl<T: Clone> Clone for SharedValue<T> {
fn clone(&self) -> Self {
let inner = self.get().clone();
Self {
value: UnsafeCell::new(inner),
}
}
}
unsafe impl<T: Send> Send for SharedValue<T> {}
unsafe impl<T: Sync> Sync for SharedValue<T> {}
impl<T> SharedValue<T> {
/// Create a new `SharedValue<T>`
pub const fn new(value: T) -> Self {
Self {
value: UnsafeCell::new(value),
}
}
/// Get a shared reference to `T`
pub fn get(&self) -> &T {
unsafe { &*self.value.get() }
}
/// Get an unique reference to `T`
pub fn get_mut(&mut self) -> &mut T {
unsafe { &mut *self.value.get() }
}
/// Unwraps the value
pub fn into_inner(self) -> T {
self.value.into_inner()
}
/// Get a mutable raw pointer to the underlying value
pub(crate) fn as_ptr(&self) -> *mut T {
self.value.get()
}
}
struct AbortOnPanic;
impl Drop for AbortOnPanic {
fn drop(&mut self) {
if std::thread::panicking() {
std::process::abort()
}
}
}
|
