summaryrefslogtreecommitdiffstats
path: root/vendor/rayon/src/iter/splitter.rs
blob: 40935ac2b0eeac50232856d5ce7354e50f0f802e (plain)
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
use super::plumbing::*;
use super::*;

use std::fmt::{self, Debug};

/// The `split` function takes arbitrary data and a closure that knows how to
/// split it, and turns this into a `ParallelIterator`.
///
/// # Examples
///
/// As a simple example, Rayon can recursively split ranges of indices
///
/// ```
/// use rayon::iter;
/// use rayon::prelude::*;
/// use std::ops::Range;
///
///
/// // We define a range of indices as follows
/// type Range1D = Range<usize>;
///
/// // Splitting it in two can be done like this
/// fn split_range1(r: Range1D) -> (Range1D, Option<Range1D>) {
///     // We are mathematically unable to split the range if there is only
///     // one point inside of it, but we could stop splitting before that.
///     if r.end - r.start <= 1 { return (r, None); }
///
///     // Here, our range is considered large enough to be splittable
///     let midpoint = r.start + (r.end - r.start) / 2;
///     (r.start..midpoint, Some(midpoint..r.end))
/// }
///
/// // By using iter::split, Rayon will split the range until it has enough work
/// // to feed the CPU cores, then give us the resulting sub-ranges
/// iter::split(0..4096, split_range1).for_each(|sub_range| {
///     // As our initial range had a power-of-two size, the final sub-ranges
///     // should have power-of-two sizes too
///     assert!((sub_range.end - sub_range.start).is_power_of_two());
/// });
/// ```
///
/// This recursive splitting can be extended to two or three dimensions,
/// to reproduce a classic "block-wise" parallelization scheme of graphics and
/// numerical simulations:
///
/// ```
/// # use rayon::iter;
/// # use rayon::prelude::*;
/// # use std::ops::Range;
/// # type Range1D = Range<usize>;
/// # fn split_range1(r: Range1D) -> (Range1D, Option<Range1D>) {
/// #     if r.end - r.start <= 1 { return (r, None); }
/// #     let midpoint = r.start + (r.end - r.start) / 2;
/// #     (r.start..midpoint, Some(midpoint..r.end))
/// # }
/// #
/// // A two-dimensional range of indices can be built out of two 1D ones
/// struct Range2D {
///     // Range of horizontal indices
///     pub rx: Range1D,
///
///     // Range of vertical indices
///     pub ry: Range1D,
/// }
///
/// // We want to recursively split them by the largest dimension until we have
/// // enough sub-ranges to feed our mighty multi-core CPU. This function
/// // carries out one such split.
/// fn split_range2(r2: Range2D) -> (Range2D, Option<Range2D>) {
///     // Decide on which axis (horizontal/vertical) the range should be split
///     let width = r2.rx.end - r2.rx.start;
///     let height = r2.ry.end - r2.ry.start;
///     if width >= height {
///         // This is a wide range, split it on the horizontal axis
///         let (split_rx, ry) = (split_range1(r2.rx), r2.ry);
///         let out1 = Range2D {
///             rx: split_rx.0,
///             ry: ry.clone(),
///         };
///         let out2 = split_rx.1.map(|rx| Range2D { rx, ry });
///         (out1, out2)
///     } else {
///         // This is a tall range, split it on the vertical axis
///         let (rx, split_ry) = (r2.rx, split_range1(r2.ry));
///         let out1 = Range2D {
///             rx: rx.clone(),
///             ry: split_ry.0,
///         };
///         let out2 = split_ry.1.map(|ry| Range2D { rx, ry, });
///         (out1, out2)
///     }
/// }
///
/// // Again, rayon can handle the recursive splitting for us
/// let range = Range2D { rx: 0..800, ry: 0..600 };
/// iter::split(range, split_range2).for_each(|sub_range| {
///     // If the sub-ranges were indeed split by the largest dimension, then
///     // if no dimension was twice larger than the other initially, this
///     // property will remain true in the final sub-ranges.
///     let width = sub_range.rx.end - sub_range.rx.start;
///     let height = sub_range.ry.end - sub_range.ry.start;
///     assert!((width / 2 <= height) && (height / 2 <= width));
/// });
/// ```
///
pub fn split<D, S>(data: D, splitter: S) -> Split<D, S>
where
    D: Send,
    S: Fn(D) -> (D, Option<D>) + Sync,
{
    Split { data, splitter }
}

/// `Split` is a parallel iterator using arbitrary data and a splitting function.
/// This struct is created by the [`split()`] function.
///
/// [`split()`]: fn.split.html
#[derive(Clone)]
pub struct Split<D, S> {
    data: D,
    splitter: S,
}

impl<D: Debug, S> Debug for Split<D, S> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("Split").field("data", &self.data).finish()
    }
}

impl<D, S> ParallelIterator for Split<D, S>
where
    D: Send,
    S: Fn(D) -> (D, Option<D>) + Sync + Send,
{
    type Item = D;

    fn drive_unindexed<C>(self, consumer: C) -> C::Result
    where
        C: UnindexedConsumer<Self::Item>,
    {
        let producer = SplitProducer {
            data: self.data,
            splitter: &self.splitter,
        };
        bridge_unindexed(producer, consumer)
    }
}

struct SplitProducer<'a, D, S> {
    data: D,
    splitter: &'a S,
}

impl<'a, D, S> UnindexedProducer for SplitProducer<'a, D, S>
where
    D: Send,
    S: Fn(D) -> (D, Option<D>) + Sync,
{
    type Item = D;

    fn split(mut self) -> (Self, Option<Self>) {
        let splitter = self.splitter;
        let (left, right) = splitter(self.data);
        self.data = left;
        (self, right.map(|data| SplitProducer { data, splitter }))
    }

    fn fold_with<F>(self, folder: F) -> F
    where
        F: Folder<Self::Item>,
    {
        folder.consume(self.data)
    }
}