timely_communication/allocator/zero_copy/
bytes_exchange.rs

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
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
//! Types and traits for sharing `Bytes`.

use std::sync::{Arc, Mutex};
use std::collections::VecDeque;

use bytes::arc::Bytes;
use super::bytes_slab::BytesSlab;

/// A target for `Bytes`.
pub trait BytesPush {
    // /// Pushes bytes at the instance.
    // fn push(&mut self, bytes: Bytes);
    /// Pushes many bytes at the instance.
    fn extend<I: IntoIterator<Item=Bytes>>(&mut self, iter: I);
}
/// A source for `Bytes`.
pub trait BytesPull {
    // /// Pulls bytes from the instance.
    // fn pull(&mut self) -> Option<Bytes>;
    /// Drains many bytes from the instance.
    fn drain_into(&mut self, vec: &mut Vec<Bytes>);
}

use std::sync::atomic::{AtomicBool, Ordering};
/// An unbounded queue of bytes intended for point-to-point communication
/// between threads. Cloning returns another handle to the same queue.
///
/// TODO: explain "extend"
#[derive(Clone)]
pub struct MergeQueue {
    queue: Arc<Mutex<VecDeque<Bytes>>>, // queue of bytes.
    buzzer: crate::buzzer::Buzzer,  // awakens receiver thread.
    panic: Arc<AtomicBool>,
}

impl MergeQueue {
    /// Allocates a new queue with an associated signal.
    pub fn new(buzzer: crate::buzzer::Buzzer) -> Self {
        MergeQueue {
            queue: Arc::new(Mutex::new(VecDeque::new())),
            buzzer,
            panic: Arc::new(AtomicBool::new(false)),
        }
    }
    /// Indicates that all input handles to the queue have dropped.
    pub fn is_complete(&self) -> bool {
        if self.panic.load(Ordering::SeqCst) { panic!("MergeQueue poisoned."); }
        Arc::strong_count(&self.queue) == 1 && self.queue.lock().expect("Failed to acquire lock").is_empty()
    }
}

impl BytesPush for MergeQueue {
    fn extend<I: IntoIterator<Item=Bytes>>(&mut self, iterator: I) {

        if self.panic.load(Ordering::SeqCst) { panic!("MergeQueue poisoned."); }

        // try to acquire lock without going to sleep (Rust's lock() might yield)
        let mut lock_ok = self.queue.try_lock();
        while let Result::Err(::std::sync::TryLockError::WouldBlock) = lock_ok {
            lock_ok = self.queue.try_lock();
        }
        let mut queue = lock_ok.expect("MergeQueue mutex poisoned.");

        let mut iterator = iterator.into_iter();
        let mut should_ping = false;
        if let Some(bytes) = iterator.next() {
            let mut tail = if let Some(mut tail) = queue.pop_back() {
                if let Err(bytes) = tail.try_merge(bytes) {
                    queue.push_back(::std::mem::replace(&mut tail, bytes));
                }
                tail
            }
            else {
                should_ping = true;
                bytes
            };

            for bytes in iterator {
                if let Err(bytes) = tail.try_merge(bytes) {
                    queue.push_back(::std::mem::replace(&mut tail, bytes));
                }
            }
            queue.push_back(tail);
        }

        // Wakeup corresponding thread *after* releasing the lock
        ::std::mem::drop(queue);
        if should_ping {
            self.buzzer.buzz();  // only signal from empty to non-empty.
        }
    }
}

impl BytesPull for MergeQueue {
    fn drain_into(&mut self, vec: &mut Vec<Bytes>) {
        if self.panic.load(Ordering::SeqCst) { panic!("MergeQueue poisoned."); }

        // try to acquire lock without going to sleep (Rust's lock() might yield)
        let mut lock_ok = self.queue.try_lock();
        while let Result::Err(::std::sync::TryLockError::WouldBlock) = lock_ok {
            lock_ok = self.queue.try_lock();
        }
        let mut queue = lock_ok.expect("MergeQueue mutex poisoned.");

        vec.extend(queue.drain(..));
    }
}

// We want to ping in the drop because a channel closing can unblock a thread waiting on
// the next bit of data to show up.
impl Drop for MergeQueue {
    fn drop(&mut self) {
        // Propagate panic information, to distinguish between clean and unclean shutdown.
        if ::std::thread::panicking() {
            self.panic.store(true, Ordering::SeqCst);
        }
        else {
            // TODO: Perhaps this aggressive ordering can relax orderings elsewhere.
            if self.panic.load(Ordering::SeqCst) { panic!("MergeQueue poisoned."); }
        }
        // Drop the queue before pinging.
        self.queue = Arc::new(Mutex::new(VecDeque::new()));
        self.buzzer.buzz();
    }
}


/// A `BytesPush` wrapper which stages writes.
pub struct SendEndpoint<P: BytesPush> {
    send: P,
    buffer: BytesSlab,
}

impl<P: BytesPush> SendEndpoint<P> {

    /// Moves `self.buffer` into `self.send`, replaces with empty buffer.
    fn send_buffer(&mut self) {
        let valid_len = self.buffer.valid().len();
        if valid_len > 0 {
            self.send.extend(Some(self.buffer.extract(valid_len)));
        }
    }

    /// Allocates a new `BytesSendEndpoint` from a shared queue.
    pub fn new(queue: P) -> Self {
        SendEndpoint {
            send: queue,
            buffer: BytesSlab::new(20),
        }
    }
    /// Makes the next `bytes` bytes valid.
    ///
    /// The current implementation also sends the bytes, to ensure early visibility.
    pub fn make_valid(&mut self, bytes: usize) {
        self.buffer.make_valid(bytes);
        self.send_buffer();
    }
    /// Acquires a prefix of `self.empty()` of length at least `capacity`.
    pub fn reserve(&mut self, capacity: usize) -> &mut [u8] {

        if self.buffer.empty().len() < capacity {
            self.send_buffer();
            self.buffer.ensure_capacity(capacity);
        }

        assert!(self.buffer.empty().len() >= capacity);
        self.buffer.empty()
    }
    /// Marks all written data as valid, makes visible.
    pub fn publish(&mut self) {
        self.send_buffer();
    }
}

impl<P: BytesPush> Drop for SendEndpoint<P> {
    fn drop(&mut self) {
        self.send_buffer();
    }
}