Initial import of rayon-1.5.0. am: 041839ceab am: d836dd6404 am: 7522a9ba00

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/rayon/+/1622436

Change-Id: I94b0e06d9da131d6f98db436ad1a178dfff2ec90

1 files changed, 86 insertions, 0 deletions

diff --git a/src/iter/take.rs b/src/iter/take.rs
new file mode 100644
index 0000000..52d15d8
--- /dev/null
+++ b/src/iter/take.rs
@@ -0,0 +1,86 @@
+use super::plumbing::*;
+use super::*;
+use std::cmp::min;
+
+/// `Take` is an iterator that iterates over the first `n` elements.
+/// This struct is created by the [`take()`] method on [`IndexedParallelIterator`]
+///
+/// [`take()`]: trait.IndexedParallelIterator.html#method.take
+/// [`IndexedParallelIterator`]: trait.IndexedParallelIterator.html
+#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
+#[derive(Debug, Clone)]
+pub struct Take<I> {
+    base: I,
+    n: usize,
+}
+
+impl<I> Take<I>
+where
+    I: IndexedParallelIterator,
+{
+    /// Creates a new `Take` iterator.
+    pub(super) fn new(base: I, n: usize) -> Self {
+        let n = min(base.len(), n);
+        Take { base, n }
+    }
+}
+
+impl<I> ParallelIterator for Take<I>
+where
+    I: IndexedParallelIterator,
+{
+    type Item = I::Item;
+
+    fn drive_unindexed<C>(self, consumer: C) -> C::Result
+    where
+        C: UnindexedConsumer<Self::Item>,
+    {
+        bridge(self, consumer)
+    }
+
+    fn opt_len(&self) -> Option<usize> {
+        Some(self.len())
+    }
+}
+
+impl<I> IndexedParallelIterator for Take<I>
+where
+    I: IndexedParallelIterator,
+{
+    fn len(&self) -> usize {
+        self.n
+    }
+
+    fn drive<C: Consumer<Self::Item>>(self, consumer: C) -> C::Result {
+        bridge(self, consumer)
+    }
+
+    fn with_producer<CB>(self, callback: CB) -> CB::Output
+    where
+        CB: ProducerCallback<Self::Item>,
+    {
+        return self.base.with_producer(Callback {
+            callback,
+            n: self.n,
+        });
+
+        struct Callback<CB> {
+            callback: CB,
+            n: usize,
+        }
+
+        impl<T, CB> ProducerCallback<T> for Callback<CB>
+        where
+            CB: ProducerCallback<T>,
+        {
+            type Output = CB::Output;
+            fn callback<P>(self, base: P) -> CB::Output
+            where
+                P: Producer<Item = T>,
+            {
+                let (producer, _) = base.split_at(self.n);
+                self.callback.callback(producer)
+            }
+        }
+    }
+}