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1 //! Parallel iterator types for [standard collections][std::collections]
2 //!
3 //! You will rarely need to interact with this module directly unless you need
4 //! to name one of the iterator types.
5 //!
6 //! [std::collections]: https://doc.rust-lang.org/stable/std/collections/
7 
8 /// Convert an iterable collection into a parallel iterator by first
9 /// collecting into a temporary `Vec`, then iterating that.
10 macro_rules! into_par_vec {
11     ($t:ty => $iter:ident<$($i:tt),*>, impl $($args:tt)*) => {
12         impl $($args)* IntoParallelIterator for $t {
13             type Item = <$t as IntoIterator>::Item;
14             type Iter = $iter<$($i),*>;
15 
16             fn into_par_iter(self) -> Self::Iter {
17                 use std::iter::FromIterator;
18                 $iter { inner: Vec::from_iter(self).into_par_iter() }
19             }
20         }
21     };
22 }
23 
24 pub mod binary_heap;
25 pub mod btree_map;
26 pub mod btree_set;
27 pub mod hash_map;
28 pub mod hash_set;
29 pub mod linked_list;
30 pub mod vec_deque;
31 
32 use self::drain_guard::DrainGuard;
33 
34 mod drain_guard {
35     use crate::iter::ParallelDrainRange;
36     use std::mem;
37     use std::ops::RangeBounds;
38 
39     /// A proxy for draining a collection by converting to a `Vec` and back.
40     ///
41     /// This is used for draining `BinaryHeap` and `VecDeque`, which both have
42     /// zero-allocation conversions to/from `Vec`, though not zero-cost:
43     /// - `BinaryHeap` will heapify from `Vec`, but at least that will be empty.
44     /// - `VecDeque` has to shift items to offset 0 when converting to `Vec`.
45     #[allow(missing_debug_implementations)]
46     pub(super) struct DrainGuard<'a, T, C: From<Vec<T>>> {
47         collection: &'a mut C,
48         vec: Vec<T>,
49     }
50 
51     impl<'a, T, C> DrainGuard<'a, T, C>
52     where
53         C: Default + From<Vec<T>>,
54         Vec<T>: From<C>,
55     {
new(collection: &'a mut C) -> Self56         pub(super) fn new(collection: &'a mut C) -> Self {
57             Self {
58                 // Temporarily steal the inner `Vec` so we can drain in place.
59                 vec: Vec::from(mem::replace(collection, C::default())),
60                 collection,
61             }
62         }
63     }
64 
65     impl<'a, T, C: From<Vec<T>>> Drop for DrainGuard<'a, T, C> {
drop(&mut self)66         fn drop(&mut self) {
67             // Restore the collection from the `Vec` with its original capacity.
68             *self.collection = C::from(mem::replace(&mut self.vec, Vec::new()));
69         }
70     }
71 
72     impl<'a, T, C> ParallelDrainRange<usize> for &'a mut DrainGuard<'_, T, C>
73     where
74         T: Send,
75         C: From<Vec<T>>,
76     {
77         type Iter = crate::vec::Drain<'a, T>;
78         type Item = T;
79 
par_drain<R: RangeBounds<usize>>(self, range: R) -> Self::Iter80         fn par_drain<R: RangeBounds<usize>>(self, range: R) -> Self::Iter {
81             self.vec.par_drain(range)
82         }
83     }
84 }
85