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
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
|
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at https://mozilla.org/MPL/2.0/. */
//! A thin atomically-reference-counted slice.
use serde::de::{Deserialize, Deserializer};
use serde::ser::{Serialize, Serializer};
use servo_arc::ThinArc;
use std::ops::Deref;
use std::ptr::NonNull;
use std::{iter, mem};
use malloc_size_of::{MallocSizeOf, MallocSizeOfOps, MallocUnconditionalSizeOf};
/// A canary that we stash in ArcSlices.
///
/// Given we cannot use a zero-sized-type for the header, since well, C++
/// doesn't have zsts, and we want to use cbindgen for this type, we may as well
/// assert some sanity at runtime.
///
/// We use an u64, to guarantee that we can use a single singleton for every
/// empty slice, even if the types they hold are aligned differently.
const ARC_SLICE_CANARY: u64 = 0xf3f3f3f3f3f3f3f3;
/// A wrapper type for a refcounted slice using ThinArc.
///
/// cbindgen:derive-eq=false
/// cbindgen:derive-neq=false
#[repr(C)]
#[derive(Debug, Eq, PartialEq, ToShmem)]
pub struct ArcSlice<T>(#[shmem(field_bound)] ThinArc<u64, T>);
impl<T> Deref for ArcSlice<T> {
type Target = [T];
#[inline]
fn deref(&self) -> &Self::Target {
debug_assert_eq!(self.0.header.header, ARC_SLICE_CANARY);
&self.0.slice
}
}
impl<T> Clone for ArcSlice<T> {
fn clone(&self) -> Self {
ArcSlice(self.0.clone())
}
}
lazy_static! {
// ThinArc doesn't support alignments greater than align_of::<u64>.
static ref EMPTY_ARC_SLICE: ArcSlice<u64> = {
ArcSlice::from_iter_leaked(iter::empty())
};
}
impl<T> Default for ArcSlice<T> {
#[allow(unsafe_code)]
fn default() -> Self {
debug_assert!(
mem::align_of::<T>() <= mem::align_of::<u64>(),
"Need to increase the alignment of EMPTY_ARC_SLICE"
);
unsafe {
let empty: ArcSlice<_> = EMPTY_ARC_SLICE.clone();
let empty: Self = mem::transmute(empty);
debug_assert_eq!(empty.len(), 0);
empty
}
}
}
impl<T: Serialize> Serialize for ArcSlice<T> {
fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
where
S: Serializer,
{
self.deref().serialize(serializer)
}
}
impl<'de, T: Deserialize<'de>> Deserialize<'de> for ArcSlice<T> {
fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
where
D: Deserializer<'de>,
{
let r = Vec::deserialize(deserializer)?;
Ok(ArcSlice::from_iter(r.into_iter()))
}
}
impl<T> ArcSlice<T> {
/// Creates an Arc for a slice using the given iterator to generate the
/// slice.
#[inline]
pub fn from_iter<I>(items: I) -> Self
where
I: Iterator<Item = T> + ExactSizeIterator,
{
if items.len() == 0 {
return Self::default();
}
ArcSlice(ThinArc::from_header_and_iter(ARC_SLICE_CANARY, items))
}
/// Creates an Arc for a slice using the given iterator to generate the
/// slice, and marks the arc as intentionally leaked from the refcount
/// logging point of view.
#[inline]
pub fn from_iter_leaked<I>(items: I) -> Self
where
I: Iterator<Item = T> + ExactSizeIterator,
{
let thin_arc = ThinArc::from_header_and_iter(ARC_SLICE_CANARY, items);
thin_arc.with_arc(|a| a.mark_as_intentionally_leaked());
ArcSlice(thin_arc)
}
/// Creates a value that can be passed via FFI, and forgets this value
/// altogether.
#[inline]
#[allow(unsafe_code)]
pub fn forget(self) -> ForgottenArcSlicePtr<T> {
let ret = unsafe {
ForgottenArcSlicePtr(NonNull::new_unchecked(self.0.ptr() as *const _ as *mut _))
};
mem::forget(self);
ret
}
/// Leaks an empty arc slice pointer, and returns it. Only to be used to
/// construct ArcSlices from FFI.
#[inline]
pub fn leaked_empty_ptr() -> *mut std::os::raw::c_void {
let empty: ArcSlice<_> = EMPTY_ARC_SLICE.clone();
let ptr = empty.0.ptr();
std::mem::forget(empty);
ptr as *mut _
}
/// Returns whether there's only one reference to this ArcSlice.
pub fn is_unique(&self) -> bool {
self.0.with_arc(|arc| arc.is_unique())
}
}
impl<T: MallocSizeOf> MallocUnconditionalSizeOf for ArcSlice<T> {
#[allow(unsafe_code)]
fn unconditional_size_of(&self, ops: &mut MallocSizeOfOps) -> usize {
let mut size = unsafe { ops.malloc_size_of(self.0.heap_ptr()) };
for el in self.iter() {
size += el.size_of(ops);
}
size
}
}
/// The inner pointer of an ArcSlice<T>, to be sent via FFI.
/// The type of the pointer is a bit of a lie, we just want to preserve the type
/// but these pointers cannot be constructed outside of this crate, so we're
/// good.
#[repr(C)]
pub struct ForgottenArcSlicePtr<T>(NonNull<T>);
|
