如何满足 Iterator trait bound 以便在这里使用 Rayon?
How to satisfy the Iterator trait bound in order to use Rayon here?
我试图通过使用 Rayon 的 par_iter
而不是 iter
来并行化 Ramer–Douglas-Peucker 线简化算法:
extern crate num_traits;
use num_traits::{Float, ToPrimitive};
extern crate rayon;
use self::rayon::prelude::*;
#[derive(PartialEq, Clone, Copy, Debug)]
pub struct Coordinate<T>
where T: Float
{
pub x: T,
pub y: T,
}
#[derive(PartialEq, Clone, Copy, Debug)]
pub struct Point<T>(pub Coordinate<T>) where T: Float;
impl<T> Point<T>
where T: Float + ToPrimitive
{
pub fn new(x: T, y: T) -> Point<T> {
Point(Coordinate { x: x, y: y })
}
pub fn x(&self) -> T {
self.0.x
}
pub fn y(&self) -> T {
self.0.y
}
}
unsafe impl<T> Send for Point<T> where T: Float {}
unsafe impl<T> Sync for Point<T> where T: Float {}
fn distance<T>(a: &Point<T>, p: &Point<T>) -> T
where T: Float
{
let (dx, dy) = (a.x() - p.x(), a.y() - p.y());
dx.hypot(dy)
}
// perpendicular distance from a point to a line
fn point_line_distance<T>(point: &Point<T>, start: &Point<T>, end: &Point<T>) -> T
where T: Float
{
if start == end {
distance(point, start)
} else {
let numerator = ((end.x() - start.x()) * (start.y() - point.y()) -
(start.x() - point.x()) * (end.y() - start.y()))
.abs();
let denominator = distance(start, end);
numerator / denominator
}
}
// Ramer–Douglas-Peucker line simplification algorithm
fn rdp<T>(points: &[Point<T>], epsilon: &T) -> Vec<Point<T>>
where T: Float + Send + Sync
{
if points.is_empty() {
return points.to_vec();
}
let mut dmax = T::zero();
let mut index: usize = 0;
let mut distance: T;
for (i, _) in points.par_iter().enumerate().take(points.len() - 1).skip(1) {
distance = point_line_distance(&points[i], &points[0], &*points.last().unwrap());
if distance > dmax {
index = i;
dmax = distance;
}
}
if dmax > *epsilon {
let mut intermediate = rdp(&points[..index + 1], &*epsilon);
intermediate.pop();
intermediate.extend_from_slice(&rdp(&points[index..], &*epsilon));
intermediate
} else {
vec![*points.first().unwrap(), *points.last().unwrap()]
}
}
#[cfg(test)]
mod test {
use super::{Point};
use super::{rdp};
#[test]
fn rdp_test() {
let mut vec = Vec::new();
vec.push(Point::new(0.0, 0.0));
vec.push(Point::new(5.0, 4.0));
vec.push(Point::new(11.0, 5.5));
vec.push(Point::new(17.3, 3.2));
vec.push(Point::new(27.8, 0.1));
let mut compare = Vec::new();
compare.push(Point::new(0.0, 0.0));
compare.push(Point::new(5.0, 4.0));
compare.push(Point::new(11.0, 5.5));
compare.push(Point::new(27.8, 0.1));
let simplified = rdp(&vec, &1.0);
assert_eq!(simplified, compare);
}
}
我已经 impl
d Send
和 Sync
用于 Point<T>
,但是当我切换到 par_iter
时,我收到以下错误:
error[E0277]: the trait bound rayon::par_iter::skip::Skip<rayon::par_iter::take::Take<rayon::par_iter::enumerate::Enumerate<rayon::par_iter::slice::SliceIter<'_, Point<T>>>>>: std::iter::Iterator is not satisfied
--> lib.rs:107:5
= note: rayon::par_iter::skip::Skip<rayon::par_iter::take::Take<rayon::par_iter::enumerate::Enumerate<rayon::par_iter::slice::SliceIter<'_, Point<T>>>>> is not an iterator; maybe try calling .iter() or a similar method
= note: required by std::iter::IntoIterator::into_iter
我不明白它在问什么。是我操作元组的问题吗?
Rayon 的并行迭代器实现 ParallelIterator
,而不是 Iterator
。特别是,这意味着您不能只将 par_iter()
放在 for-loop header 中并期望它突然平行。 for
是连续的。
由于您的原始代码不是根据迭代器函数编写的,而是关于循环的,因此您不能简单地通过切换到 par_iter()
来并行化它,而必须实际重新设计代码。
特别是,代码的失败部分似乎是在实现 max_by_key
函数。
我试图通过使用 Rayon 的 par_iter
而不是 iter
来并行化 Ramer–Douglas-Peucker 线简化算法:
extern crate num_traits;
use num_traits::{Float, ToPrimitive};
extern crate rayon;
use self::rayon::prelude::*;
#[derive(PartialEq, Clone, Copy, Debug)]
pub struct Coordinate<T>
where T: Float
{
pub x: T,
pub y: T,
}
#[derive(PartialEq, Clone, Copy, Debug)]
pub struct Point<T>(pub Coordinate<T>) where T: Float;
impl<T> Point<T>
where T: Float + ToPrimitive
{
pub fn new(x: T, y: T) -> Point<T> {
Point(Coordinate { x: x, y: y })
}
pub fn x(&self) -> T {
self.0.x
}
pub fn y(&self) -> T {
self.0.y
}
}
unsafe impl<T> Send for Point<T> where T: Float {}
unsafe impl<T> Sync for Point<T> where T: Float {}
fn distance<T>(a: &Point<T>, p: &Point<T>) -> T
where T: Float
{
let (dx, dy) = (a.x() - p.x(), a.y() - p.y());
dx.hypot(dy)
}
// perpendicular distance from a point to a line
fn point_line_distance<T>(point: &Point<T>, start: &Point<T>, end: &Point<T>) -> T
where T: Float
{
if start == end {
distance(point, start)
} else {
let numerator = ((end.x() - start.x()) * (start.y() - point.y()) -
(start.x() - point.x()) * (end.y() - start.y()))
.abs();
let denominator = distance(start, end);
numerator / denominator
}
}
// Ramer–Douglas-Peucker line simplification algorithm
fn rdp<T>(points: &[Point<T>], epsilon: &T) -> Vec<Point<T>>
where T: Float + Send + Sync
{
if points.is_empty() {
return points.to_vec();
}
let mut dmax = T::zero();
let mut index: usize = 0;
let mut distance: T;
for (i, _) in points.par_iter().enumerate().take(points.len() - 1).skip(1) {
distance = point_line_distance(&points[i], &points[0], &*points.last().unwrap());
if distance > dmax {
index = i;
dmax = distance;
}
}
if dmax > *epsilon {
let mut intermediate = rdp(&points[..index + 1], &*epsilon);
intermediate.pop();
intermediate.extend_from_slice(&rdp(&points[index..], &*epsilon));
intermediate
} else {
vec![*points.first().unwrap(), *points.last().unwrap()]
}
}
#[cfg(test)]
mod test {
use super::{Point};
use super::{rdp};
#[test]
fn rdp_test() {
let mut vec = Vec::new();
vec.push(Point::new(0.0, 0.0));
vec.push(Point::new(5.0, 4.0));
vec.push(Point::new(11.0, 5.5));
vec.push(Point::new(17.3, 3.2));
vec.push(Point::new(27.8, 0.1));
let mut compare = Vec::new();
compare.push(Point::new(0.0, 0.0));
compare.push(Point::new(5.0, 4.0));
compare.push(Point::new(11.0, 5.5));
compare.push(Point::new(27.8, 0.1));
let simplified = rdp(&vec, &1.0);
assert_eq!(simplified, compare);
}
}
我已经 impl
d Send
和 Sync
用于 Point<T>
,但是当我切换到 par_iter
时,我收到以下错误:
error[E0277]: the trait bound rayon::par_iter::skip::Skip<rayon::par_iter::take::Take<rayon::par_iter::enumerate::Enumerate<rayon::par_iter::slice::SliceIter<'_, Point<T>>>>>: std::iter::Iterator is not satisfied
--> lib.rs:107:5
= note: rayon::par_iter::skip::Skip<rayon::par_iter::take::Take<rayon::par_iter::enumerate::Enumerate<rayon::par_iter::slice::SliceIter<'_, Point<T>>>>> is not an iterator; maybe try calling .iter() or a similar method
= note: required by std::iter::IntoIterator::into_iter
我不明白它在问什么。是我操作元组的问题吗?
Rayon 的并行迭代器实现 ParallelIterator
,而不是 Iterator
。特别是,这意味着您不能只将 par_iter()
放在 for-loop header 中并期望它突然平行。 for
是连续的。
由于您的原始代码不是根据迭代器函数编写的,而是关于循环的,因此您不能简单地通过切换到 par_iter()
来并行化它,而必须实际重新设计代码。
特别是,代码的失败部分似乎是在实现 max_by_key
函数。