From 041839ceabbc67165512fde0d33c91347b758487 Mon Sep 17 00:00:00 2001
From: Jakub Kotur <qtr@google.com>
Date: Mon, 21 Dec 2020 17:28:15 +0100
Subject: Initial import of rayon-1.5.0.

Bug: 155309706
Change-Id: I6ff7de1cb89d093d7938abf78d586ed76da85b0d
---
 src/iter/flat_map.rs | 154 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 154 insertions(+)
 create mode 100644 src/iter/flat_map.rs

(limited to 'src/iter/flat_map.rs')

diff --git a/src/iter/flat_map.rs b/src/iter/flat_map.rs
new file mode 100644
index 0000000..f264e1e
--- /dev/null
+++ b/src/iter/flat_map.rs
@@ -0,0 +1,154 @@
+use super::plumbing::*;
+use super::*;
+
+use std::fmt::{self, Debug};
+
+/// `FlatMap` maps each element to a parallel iterator, then flattens these iterators together.
+/// This struct is created by the [`flat_map()`] method on [`ParallelIterator`]
+///
+/// [`flat_map()`]: trait.ParallelIterator.html#method.flat_map
+/// [`ParallelIterator`]: trait.ParallelIterator.html
+#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
+#[derive(Clone)]
+pub struct FlatMap<I: ParallelIterator, F> {
+    base: I,
+    map_op: F,
+}
+
+impl<I: ParallelIterator + Debug, F> Debug for FlatMap<I, F> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("FlatMap").field("base", &self.base).finish()
+    }
+}
+
+impl<I: ParallelIterator, F> FlatMap<I, F> {
+    /// Creates a new `FlatMap` iterator.
+    pub(super) fn new(base: I, map_op: F) -> Self {
+        FlatMap { base, map_op }
+    }
+}
+
+impl<I, F, PI> ParallelIterator for FlatMap<I, F>
+where
+    I: ParallelIterator,
+    F: Fn(I::Item) -> PI + Sync + Send,
+    PI: IntoParallelIterator,
+{
+    type Item = PI::Item;
+
+    fn drive_unindexed<C>(self, consumer: C) -> C::Result
+    where
+        C: UnindexedConsumer<Self::Item>,
+    {
+        let consumer = FlatMapConsumer::new(consumer, &self.map_op);
+        self.base.drive_unindexed(consumer)
+    }
+}
+
+/// ////////////////////////////////////////////////////////////////////////
+/// Consumer implementation
+
+struct FlatMapConsumer<'f, C, F> {
+    base: C,
+    map_op: &'f F,
+}
+
+impl<'f, C, F> FlatMapConsumer<'f, C, F> {
+    fn new(base: C, map_op: &'f F) -> Self {
+        FlatMapConsumer { base, map_op }
+    }
+}
+
+impl<'f, T, U, C, F> Consumer<T> for FlatMapConsumer<'f, C, F>
+where
+    C: UnindexedConsumer<U::Item>,
+    F: Fn(T) -> U + Sync,
+    U: IntoParallelIterator,
+{
+    type Folder = FlatMapFolder<'f, C, F, C::Result>;
+    type Reducer = C::Reducer;
+    type Result = C::Result;
+
+    fn split_at(self, index: usize) -> (Self, Self, C::Reducer) {
+        let (left, right, reducer) = self.base.split_at(index);
+        (
+            FlatMapConsumer::new(left, self.map_op),
+            FlatMapConsumer::new(right, self.map_op),
+            reducer,
+        )
+    }
+
+    fn into_folder(self) -> Self::Folder {
+        FlatMapFolder {
+            base: self.base,
+            map_op: self.map_op,
+            previous: None,
+        }
+    }
+
+    fn full(&self) -> bool {
+        self.base.full()
+    }
+}
+
+impl<'f, T, U, C, F> UnindexedConsumer<T> for FlatMapConsumer<'f, C, F>
+where
+    C: UnindexedConsumer<U::Item>,
+    F: Fn(T) -> U + Sync,
+    U: IntoParallelIterator,
+{
+    fn split_off_left(&self) -> Self {
+        FlatMapConsumer::new(self.base.split_off_left(), self.map_op)
+    }
+
+    fn to_reducer(&self) -> Self::Reducer {
+        self.base.to_reducer()
+    }
+}
+
+struct FlatMapFolder<'f, C, F, R> {
+    base: C,
+    map_op: &'f F,
+    previous: Option<R>,
+}
+
+impl<'f, T, U, C, F> Folder<T> for FlatMapFolder<'f, C, F, C::Result>
+where
+    C: UnindexedConsumer<U::Item>,
+    F: Fn(T) -> U + Sync,
+    U: IntoParallelIterator,
+{
+    type Result = C::Result;
+
+    fn consume(self, item: T) -> Self {
+        let map_op = self.map_op;
+        let par_iter = map_op(item).into_par_iter();
+        let consumer = self.base.split_off_left();
+        let result = par_iter.drive_unindexed(consumer);
+
+        let previous = match self.previous {
+            None => Some(result),
+            Some(previous) => {
+                let reducer = self.base.to_reducer();
+                Some(reducer.reduce(previous, result))
+            }
+        };
+
+        FlatMapFolder {
+            base: self.base,
+            map_op,
+            previous,
+        }
+    }
+
+    fn complete(self) -> Self::Result {
+        match self.previous {
+            Some(previous) => previous,
+            None => self.base.into_folder().complete(),
+        }
+    }
+
+    fn full(&self) -> bool {
+        self.base.full()
+    }
+}
-- 
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