syncpool 0.1.6

A thread-friendly library for recycle of heavy and heap-based objects to reduce allocation and memory pressure
Documentation 
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

#![allow(unused)]

use std::mem::ManuallyDrop;
use std::ops::{Deref, DerefMut};
use std::ptr;
use std::sync::{
    Arc,
    mpsc::{SyncSender, Receiver, TrySendError},
    atomic::{AtomicPtr, AtomicBool, Ordering},
};

enum Message<T> {
    Shutdown,
    Release(*mut ManuallyDrop<Box<T>>),
}

#[derive(Default)]
pub struct Container<T>
    where T: Default
{
    val: ManuallyDrop<Box<T>>,
    chan: Option<SyncSender<Message<T>>>,
}

impl<T> Deref for Container<T>
    where T: Default
{
    type Target = T;

    fn deref(&self) -> &Self::Target {
        &self.val
    }
}

impl<T> DerefMut for Container<T>
    where T: Default
{
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.val
    }
}

impl<T> Drop for Container<T>
    where T: Default
{
    fn drop(&mut self) {
        if self.chan.is_none() {
            unsafe { ManuallyDrop::drop(&mut self.val); }
            return;
        }

        self.chan
            .as_ref()
            .unwrap()
            .try_send(Message::Release(&mut self.val as *mut ManuallyDrop<Box<T>>))
            .map_err(|err| {
                // extract the content
                let msg = match err {
                    TrySendError::Full(m) => m,
                    TrySendError::Disconnected(m) => m,
                };

                // failed to return the value, must manually drop the value now
                if let Message::Release(ptr) = msg {
                    unsafe { ManuallyDrop::drop(&mut *ptr); }
                };
            });
    }
}

struct Slot<T> {
    val: *mut ManuallyDrop<Box<T>>,
    next: AtomicPtr<Slot<T>>,
}

impl<T> Slot<T>
    where T: Default
{
    fn new(val: T) -> Slot<T> {
        let mut wrapper = ManuallyDrop::new(Box::new(val));
        Slot {
            val: &mut wrapper as *mut ManuallyDrop<Box<T>>,
            next: AtomicPtr::new(ptr::null_mut()),
        }
    }

    fn take(mut self, chan: SyncSender<Message<T>>) -> Container<T> {
        Container {
            val: unsafe { self.val.read() },
            chan: Some(chan),
        }
    }
}

struct Inner<T> {
    head: *mut Slot<T>,
    tail: *mut Slot<T>,
    chan: (SyncSender<Message<T>>, Receiver<Message<T>>),
    close: AtomicBool,
}

impl<T> Inner<T>
    where T: Default
{
    fn get(&mut self) -> Container<T> {
        if self.close.load(Ordering::Acquire) {
            return Default::default()
        }

        if let Ok(msg) = self.chan.1.try_recv() {
            let val = match msg {
                Message::Shutdown => {
                    self.close.store(true, Ordering::SeqCst);
                    Default::default()
                }
                Message::Release(p) => {
                    Container {
                        val: unsafe { ptr::read(p) },
                        chan: Some(self.chan.0.clone()),
                    }
                }
            };

            return val;
        }

        Default::default()
    }
}

pub struct Pool<T> {
    inner: Arc<Inner<T>>,
}