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

use crate::{
    iter::buffered::slice::BufferedSlice, next::NextChunk, ConcurrentIter, ConcurrentIterX, Next,
};
use std::sync::atomic::{AtomicUsize, Ordering};

/// A concurrent iterator over a slice yielding references to the elements.
pub struct ConIterOfSlice<'a, T: Send + Sync> {
    slice: &'a [T],
    counter: AtomicUsize,
}

impl<'a, T: Send + Sync> std::fmt::Debug for ConIterOfSlice<'a, T> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        super::helpers::fmt_iter(f, "ConIterOfSlice", Some(self.slice.len()), &self.counter)
    }
}

impl<'a, T: Send + Sync> ConIterOfSlice<'a, T> {
    /// Creates a concurrent iterator for the given `slice`.
    pub fn new(slice: &'a [T]) -> Self {
        Self {
            slice,
            counter: 0.into(),
        }
    }

    /// Returns a reference to the underlying slice.
    pub(crate) fn as_slice(&self) -> &'a [T] {
        self.slice
    }

    #[inline(always)]
    fn get(&self, item_idx: usize) -> Option<&'a T> {
        self.slice.get(item_idx)
    }

    #[inline(always)]
    pub(crate) fn progress_and_get_begin_idx(&self, number_to_fetch: usize) -> Option<usize> {
        let begin_idx = self.counter.fetch_add(number_to_fetch, Ordering::Relaxed);
        match begin_idx < self.slice.len() {
            true => Some(begin_idx),
            _ => None,
        }
    }
}

impl<'a, T: Send + Sync> From<&'a [T]> for ConIterOfSlice<'a, T> {
    /// Creates a concurrent iterator for the given `slice`.
    fn from(slice: &'a [T]) -> Self {
        Self::new(slice)
    }
}

impl<'a, T: Send + Sync> Clone for ConIterOfSlice<'a, T> {
    fn clone(&self) -> Self {
        let counter = self.counter.load(Ordering::SeqCst).into();
        Self {
            slice: self.slice,
            counter,
        }
    }
}

unsafe impl<'a, T: Send + Sync> Sync for ConIterOfSlice<'a, T> {}

unsafe impl<'a, T: Send + Sync> Send for ConIterOfSlice<'a, T> {}

// AtomicIter -> ConcurrentIter

impl<'a, T: Send + Sync> ConcurrentIterX for ConIterOfSlice<'a, T> {
    type Item = &'a T;

    type SeqIter = std::iter::Skip<std::slice::Iter<'a, T>>;

    type BufferedIterX = BufferedSlice<T>;

    fn into_seq_iter(self) -> Self::SeqIter {
        let current = self.counter.load(Ordering::Acquire);
        self.slice.iter().skip(current)
    }

    fn next_chunk_x(&self, chunk_size: usize) -> Option<impl ExactSizeIterator<Item = Self::Item>> {
        let begin_idx = self
            .progress_and_get_begin_idx(chunk_size)
            .unwrap_or(self.slice.len());
        let end_idx = (begin_idx + chunk_size)
            .min(self.slice.len())
            .max(begin_idx);

        match begin_idx < end_idx {
            true => Some(self.slice[begin_idx..end_idx].iter()),
            false => None,
        }
    }

    fn next(&self) -> Option<Self::Item> {
        let idx = self.counter.fetch_add(1, Ordering::Acquire);
        self.get(idx)
    }

    #[inline(always)]
    fn try_get_len(&self) -> Option<usize> {
        let current = self.counter.load(Ordering::Acquire);
        let initial_len = self.slice.len();
        let len = match current.cmp(&initial_len) {
            std::cmp::Ordering::Less => initial_len - current,
            _ => 0,
        };
        Some(len)
    }

    #[inline(always)]
    fn try_get_initial_len(&self) -> Option<usize> {
        Some(self.slice.len())
    }

    fn skip_to_end(&self) {
        let _ = self.counter.fetch_max(self.slice.len(), Ordering::Acquire);
    }
}

impl<'a, T: Send + Sync> ConcurrentIter for ConIterOfSlice<'a, T> {
    type BufferedIter = Self::BufferedIterX;

    #[inline(always)]
    fn next_id_and_value(&self) -> Option<Next<Self::Item>> {
        let idx = self.counter.fetch_add(1, Ordering::Acquire);
        self.get(idx).map(|value| Next { idx, value })
    }

    #[inline(always)]
    fn next_chunk(
        &self,
        chunk_size: usize,
    ) -> Option<NextChunk<Self::Item, impl ExactSizeIterator<Item = Self::Item>>> {
        let begin_idx = self
            .progress_and_get_begin_idx(chunk_size)
            .unwrap_or(self.slice.len());
        let end_idx = (begin_idx + chunk_size)
            .min(self.slice.len())
            .max(begin_idx);

        match begin_idx < end_idx {
            true => {
                let values = self.slice[begin_idx..end_idx].iter();
                Some(NextChunk { begin_idx, values })
            }
            false => None,
        }
    }
}