forked from vmware-archive/node-replicated-kernel
-
Notifications
You must be signed in to change notification settings - Fork 0
Expand file tree
/
Copy pathmpmc.rs
More file actions
159 lines (139 loc) · 4.66 KB
/
Copy pathmpmc.rs
File metadata and controls
159 lines (139 loc) · 4.66 KB
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
// Copyright © 2021 VMware, Inc. All Rights Reserved.
// Copyright © 2010-2011 Dmitry Vyukov. All rights reserved.
// SPDX-License-Identifier: BSD-2-Clause
// http://www.1024cores.net/home/lock-free-algorithms/queues/bounded-mpmc-queue
// This queue is copy pasted from old rust stdlib.
#![allow(warnings)] // For now...
use alloc::sync::Arc;
use alloc::vec::Vec;
use core::cell::UnsafeCell;
use core::sync::atomic::AtomicUsize;
use core::sync::atomic::Ordering::{Acquire, Relaxed, Release};
use fallible_collections::vec::FallibleVec;
use fallible_collections::vec::TryCollect;
use crate::error::KError;
use crate::prelude::*;
struct Node<T> {
sequence: AtomicUsize,
value: Option<T>,
}
unsafe impl<T: Send> Send for Node<T> {}
unsafe impl<T: Sync> Sync for Node<T> {}
struct State<T> {
buffer: CachePadded<Vec<UnsafeCell<Node<T>>>>,
mask: usize,
enqueue_pos: CachePadded<AtomicUsize>,
dequeue_pos: CachePadded<AtomicUsize>,
}
unsafe impl<T: Send> Send for State<T> {}
unsafe impl<T: Sync> Sync for State<T> {}
pub(crate) struct Queue<T> {
state: Arc<State<T>>,
}
impl<T: Send> State<T> {
fn with_capacity(capacity: usize) -> Result<State<T>, KError> {
let capacity = if capacity < 2 || (capacity & (capacity - 1)) != 0 {
if capacity < 2 {
2
} else {
// use next power of 2 as capacity
capacity.next_power_of_two()
}
} else {
capacity
};
let buffer = (0..capacity)
.map(|i| {
UnsafeCell::new(Node {
sequence: AtomicUsize::new(i),
value: None,
})
})
.try_collect::<Vec<_>>()?;
Ok(State {
buffer: CachePadded::new(buffer),
mask: capacity - 1,
enqueue_pos: CachePadded::new(AtomicUsize::new(0)),
dequeue_pos: CachePadded::new(AtomicUsize::new(0)),
})
}
fn push(&self, value: T) -> Result<(), T> {
let mask = self.mask;
let mut pos = self.enqueue_pos.load(Relaxed);
loop {
let node = &self.buffer[pos & mask];
let seq = unsafe { (*node.get()).sequence.load(Acquire) };
let diff: isize = seq as isize - pos as isize;
if diff == 0 {
match self
.enqueue_pos
.compare_exchange_weak(pos, pos + 1, Relaxed, Relaxed)
{
Ok(enqueue_pos) => {
debug_assert_eq!(enqueue_pos, pos);
unsafe {
(*node.get()).value = Some(value);
(*node.get()).sequence.store(pos + 1, Release);
}
break;
}
Err(enqueue_pos) => pos = enqueue_pos,
}
} else if diff < 0 {
return Err(value);
} else {
pos = self.enqueue_pos.load(Relaxed);
}
}
Ok(())
}
fn pop(&self) -> Option<T> {
let mask = self.mask;
let mut pos = self.dequeue_pos.load(Relaxed);
loop {
let node = &self.buffer[pos & mask];
let seq = unsafe { (*node.get()).sequence.load(Acquire) };
let diff: isize = seq as isize - (pos + 1) as isize;
if diff == 0 {
match self
.dequeue_pos
.compare_exchange_weak(pos, pos + 1, Relaxed, Relaxed)
{
Ok(dequeue_pos) => {
debug_assert_eq!(dequeue_pos, pos);
unsafe {
let value = (*node.get()).value.take();
(*node.get()).sequence.store(pos + mask + 1, Release);
return value;
}
}
Err(dequeue_pos) => pos = dequeue_pos,
}
} else if diff < 0 {
return None;
} else {
pos = self.dequeue_pos.load(Relaxed);
}
}
}
}
impl<T: Send> Queue<T> {
pub(crate) fn with_capacity(capacity: usize) -> Result<Queue<T>, KError> {
Ok(Queue {
state: Arc::try_new(State::with_capacity(capacity)?)?,
})
}
pub(crate) fn push(&self, value: T) -> Result<(), T> {
self.state.push(value)
}
pub(crate) fn pop(&self) -> Option<T> {
self.state.pop()
}
}
impl<T: Send> Clone for Queue<T> {
fn clone(&self) -> Queue<T> {
Queue {
state: self.state.clone(),
}
}
}