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
use crate::loom::sync::atomic::AtomicUsize;
use crate::runtime::io::ScheduledIo;
use crate::util::linked_list::{self, LinkedList};

use std::io;
use std::ptr::NonNull;
use std::sync::atomic::Ordering::{Acquire, Release};
use std::sync::Arc;

pub(super) struct RegistrationSet {
    num_pending_release: AtomicUsize,
}

pub(super) struct Synced {
    // True when the I/O driver shutdown. At this point, no more registrations
    // should be added to the set.
    is_shutdown: bool,

    // List of all registrations tracked by the set
    registrations: LinkedList<Arc<ScheduledIo>, ScheduledIo>,

    // Registrations that are pending drop. When a `Registration` is dropped, it
    // stores its `ScheduledIo` in this list. The I/O driver is responsible for
    // dropping it. This ensures the `ScheduledIo` is not freed while it can
    // still be included in an I/O event.
    pending_release: Vec<Arc<ScheduledIo>>,
}

impl RegistrationSet {
    pub(super) fn new() -> (RegistrationSet, Synced) {
        let set = RegistrationSet {
            num_pending_release: AtomicUsize::new(0),
        };

        let synced = Synced {
            is_shutdown: false,
            registrations: LinkedList::new(),
            pending_release: Vec::with_capacity(16),
        };

        (set, synced)
    }

    pub(super) fn is_shutdown(&self, synced: &Synced) -> bool {
        synced.is_shutdown
    }

    /// Returns `true` if there are registrations that need to be released
    pub(super) fn needs_release(&self) -> bool {
        self.num_pending_release.load(Acquire) != 0
    }

    pub(super) fn allocate(&self, synced: &mut Synced) -> io::Result<Arc<ScheduledIo>> {
        if synced.is_shutdown {
            return Err(io::Error::new(
                io::ErrorKind::Other,
                crate::util::error::RUNTIME_SHUTTING_DOWN_ERROR,
            ));
        }

        let ret = Arc::new(ScheduledIo::default());

        // Push a ref into the list of all resources.
        synced.registrations.push_front(ret.clone());

        Ok(ret)
    }

    // Returns `true` if the caller should unblock the I/O driver to purge
    // registrations pending release.
    pub(super) fn deregister(&self, synced: &mut Synced, registration: &Arc<ScheduledIo>) -> bool {
        // Kind of arbitrary, but buffering 16 `ScheduledIo`s doesn't seem like much
        const NOTIFY_AFTER: usize = 16;

        synced.pending_release.push(registration.clone());

        let len = synced.pending_release.len();
        self.num_pending_release.store(len, Release);

        len == NOTIFY_AFTER
    }

    pub(super) fn shutdown(&self, synced: &mut Synced) -> Vec<Arc<ScheduledIo>> {
        if synced.is_shutdown {
            return vec![];
        }

        synced.is_shutdown = true;
        synced.pending_release.clear();

        // Building a vec of all outstanding I/O handles could be expensive, but
        // this is the shutdown operation. In theory, shutdowns should be
        // "clean" with no outstanding I/O resources. Even if it is slow, we
        // aren't optimizing for shutdown.
        let mut ret = vec![];

        while let Some(io) = synced.registrations.pop_back() {
            ret.push(io);
        }

        ret
    }

    pub(super) fn release(&self, synced: &mut Synced) {
        for io in synced.pending_release.drain(..) {
            // safety: the registration is part of our list
            let _ = unsafe { synced.registrations.remove(io.as_ref().into()) };
        }

        self.num_pending_release.store(0, Release);
    }
}

// Safety: `Arc` pins the inner data
unsafe impl linked_list::Link for Arc<ScheduledIo> {
    type Handle = Arc<ScheduledIo>;
    type Target = ScheduledIo;

    fn as_raw(handle: &Self::Handle) -> NonNull<ScheduledIo> {
        // safety: Arc::as_ptr never returns null
        unsafe { NonNull::new_unchecked(Arc::as_ptr(handle) as *mut _) }
    }

    unsafe fn from_raw(ptr: NonNull<Self::Target>) -> Arc<ScheduledIo> {
        // safety: the linked list currently owns a ref count
        unsafe { Arc::from_raw(ptr.as_ptr() as *const _) }
    }

    unsafe fn pointers(
        target: NonNull<Self::Target>,
    ) -> NonNull<linked_list::Pointers<ScheduledIo>> {
        NonNull::new_unchecked(target.as_ref().linked_list_pointers.get())
    }
}