rayon/iter/
chunks.rs

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1use std::cmp::min;
2
3use super::plumbing::*;
4use super::*;
5use crate::math::div_round_up;
6
7/// `Chunks` is an iterator that groups elements of an underlying iterator.
8///
9/// This struct is created by the [`chunks()`] method on [`IndexedParallelIterator`]
10///
11/// [`chunks()`]: trait.IndexedParallelIterator.html#method.chunks
12/// [`IndexedParallelIterator`]: trait.IndexedParallelIterator.html
13#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
14#[derive(Debug, Clone)]
15pub struct Chunks<I>
16where
17    I: IndexedParallelIterator,
18{
19    size: usize,
20    i: I,
21}
22
23impl<I> Chunks<I>
24where
25    I: IndexedParallelIterator,
26{
27    /// Creates a new `Chunks` iterator
28    pub(super) fn new(i: I, size: usize) -> Self {
29        Chunks { i, size }
30    }
31}
32
33impl<I> ParallelIterator for Chunks<I>
34where
35    I: IndexedParallelIterator,
36{
37    type Item = Vec<I::Item>;
38
39    fn drive_unindexed<C>(self, consumer: C) -> C::Result
40    where
41        C: Consumer<Vec<I::Item>>,
42    {
43        bridge(self, consumer)
44    }
45
46    fn opt_len(&self) -> Option<usize> {
47        Some(self.len())
48    }
49}
50
51impl<I> IndexedParallelIterator for Chunks<I>
52where
53    I: IndexedParallelIterator,
54{
55    fn drive<C>(self, consumer: C) -> C::Result
56    where
57        C: Consumer<Self::Item>,
58    {
59        bridge(self, consumer)
60    }
61
62    fn len(&self) -> usize {
63        div_round_up(self.i.len(), self.size)
64    }
65
66    fn with_producer<CB>(self, callback: CB) -> CB::Output
67    where
68        CB: ProducerCallback<Self::Item>,
69    {
70        let len = self.i.len();
71        return self.i.with_producer(Callback {
72            size: self.size,
73            len,
74            callback,
75        });
76
77        struct Callback<CB> {
78            size: usize,
79            len: usize,
80            callback: CB,
81        }
82
83        impl<T, CB> ProducerCallback<T> for Callback<CB>
84        where
85            CB: ProducerCallback<Vec<T>>,
86        {
87            type Output = CB::Output;
88
89            fn callback<P>(self, base: P) -> CB::Output
90            where
91                P: Producer<Item = T>,
92            {
93                self.callback.callback(ChunkProducer {
94                    chunk_size: self.size,
95                    len: self.len,
96                    base,
97                })
98            }
99        }
100    }
101}
102
103struct ChunkProducer<P>
104where
105    P: Producer,
106{
107    chunk_size: usize,
108    len: usize,
109    base: P,
110}
111
112impl<P> Producer for ChunkProducer<P>
113where
114    P: Producer,
115{
116    type Item = Vec<P::Item>;
117    type IntoIter = ChunkSeq<P>;
118
119    fn into_iter(self) -> Self::IntoIter {
120        ChunkSeq {
121            chunk_size: self.chunk_size,
122            len: self.len,
123            inner: if self.len > 0 { Some(self.base) } else { None },
124        }
125    }
126
127    fn split_at(self, index: usize) -> (Self, Self) {
128        let elem_index = min(index * self.chunk_size, self.len);
129        let (left, right) = self.base.split_at(elem_index);
130        (
131            ChunkProducer {
132                chunk_size: self.chunk_size,
133                len: elem_index,
134                base: left,
135            },
136            ChunkProducer {
137                chunk_size: self.chunk_size,
138                len: self.len - elem_index,
139                base: right,
140            },
141        )
142    }
143
144    fn min_len(&self) -> usize {
145        div_round_up(self.base.min_len(), self.chunk_size)
146    }
147
148    fn max_len(&self) -> usize {
149        self.base.max_len() / self.chunk_size
150    }
151}
152
153struct ChunkSeq<P> {
154    chunk_size: usize,
155    len: usize,
156    inner: Option<P>,
157}
158
159impl<P> Iterator for ChunkSeq<P>
160where
161    P: Producer,
162{
163    type Item = Vec<P::Item>;
164
165    fn next(&mut self) -> Option<Self::Item> {
166        let producer = self.inner.take()?;
167        if self.len > self.chunk_size {
168            let (left, right) = producer.split_at(self.chunk_size);
169            self.inner = Some(right);
170            self.len -= self.chunk_size;
171            Some(left.into_iter().collect())
172        } else {
173            debug_assert!(self.len > 0);
174            self.len = 0;
175            Some(producer.into_iter().collect())
176        }
177    }
178
179    fn size_hint(&self) -> (usize, Option<usize>) {
180        let len = self.len();
181        (len, Some(len))
182    }
183}
184
185impl<P> ExactSizeIterator for ChunkSeq<P>
186where
187    P: Producer,
188{
189    #[inline]
190    fn len(&self) -> usize {
191        div_round_up(self.len, self.chunk_size)
192    }
193}
194
195impl<P> DoubleEndedIterator for ChunkSeq<P>
196where
197    P: Producer,
198{
199    fn next_back(&mut self) -> Option<Self::Item> {
200        let producer = self.inner.take()?;
201        if self.len > self.chunk_size {
202            let mut size = self.len % self.chunk_size;
203            if size == 0 {
204                size = self.chunk_size;
205            }
206            let (left, right) = producer.split_at(self.len - size);
207            self.inner = Some(left);
208            self.len -= size;
209            Some(right.into_iter().collect())
210        } else {
211            debug_assert!(self.len > 0);
212            self.len = 0;
213            Some(producer.into_iter().collect())
214        }
215    }
216}
rayon/iter/chunks.rs

rayon/iter/
chunks.rs
