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<main>
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<h1 id="任务并行处理"><a class="header" href="#任务并行处理">任务并行处理</a></h1>
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<h3 id="并行修改数组中的元素"><a class="header" href="#并行修改数组中的元素">并行修改数组中的元素</a></h3>
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<p><a href="https://docs.rs/rayon/1.5.1/rayon/index.html">rayon</a> 提供了一个 <a href="https://docs.rs/rayon/*/rayon/iter/trait.IntoParallelRefMutIterator.html#tymethod.par_iter_mut">par_iter_mut</a> 方法用于并行化迭代一个数据集合。</p>
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<pre><pre class="playground"><code class="language-rust editable edition2021">use rayon::prelude::*;
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fn main() {
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let mut arr = [0, 7, 9, 11];
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arr.par_iter_mut().for_each(|p| *p -= 1);
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println!("{:?}", arr);
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}
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</code></pre></pre>
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<h3 id="并行测试集合中的元素是否满足给定的条件"><a class="header" href="#并行测试集合中的元素是否满足给定的条件">并行测试集合中的元素是否满足给定的条件</a></h3>
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<p><a href="https://docs.rs/rayon/*/rayon/iter/trait.ParallelIterator.html#method.any">rayon::any</a> 和 <a href="https://docs.rs/rayon/*/rayon/iter/trait.ParallelIterator.html#method.all">rayon::all</a> 类似于 <a href="https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.any">std::any</a> / <a href="https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.all">std::all</a> ，但是是并行版本的。</p>
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<ul>
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<li><code>rayon::any</code> 并行检查迭代器中是否有任何元素满足给定的条件，一旦发现符合条件的元素，就立即返回</li>
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<li><code>rayon::all</code> 并行检查迭代器中的所有元素是否满足给定的条件，一旦发现不满足条件的元素，就立即返回</li>
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</ul>
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<pre><pre class="playground"><code class="language-rust editable edition2021">use rayon::prelude::*;
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fn main() {
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let mut vec = vec![2, 4, 6, 8];
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assert!(!vec.par_iter().any(|n| (*n % 2) != 0));
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assert!(vec.par_iter().all(|n| (*n % 2) == 0));
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assert!(!vec.par_iter().any(|n| *n > 8 ));
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assert!(vec.par_iter().all(|n| *n <= 8 ));
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vec.push(9);
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assert!(vec.par_iter().any(|n| (*n % 2) != 0));
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assert!(!vec.par_iter().all(|n| (*n % 2) == 0));
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assert!(vec.par_iter().any(|n| *n > 8 ));
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assert!(!vec.par_iter().all(|n| *n <= 8 ));
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}
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</code></pre></pre>
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<h3 id="使用给定条件并行搜索"><a class="header" href="#使用给定条件并行搜索">使用给定条件并行搜索</a></h3>
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<p>下面例子使用 <a href="https://docs.rs/rayon/*/rayon/iter/trait.IntoParallelRefIterator.html#tymethod.par_iter">par_iter</a> 和 <a href="https://docs.rs/rayon/*/rayon/iter/trait.ParallelIterator.html#method.find_any">rayon::find_any</a> 来并行搜索一个数组，直到找到任意一个满足条件的元素。</p>
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<p>如果有多个元素满足条件，<code>rayon</code> 会返回第一个找到的元素，注意：第一个找到的元素未必是数组中的顺序最靠前的那个。</p>
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<pre><pre class="playground"><code class="language-rust editable edition2021">use rayon::prelude::*;
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fn main() {
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let v = vec![6, 2, 1, 9, 3, 8, 11];
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// 这里使用了 `&&x` 的形式，大家可以在以下链接阅读更多 https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.find
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let f1 = v.par_iter().find_any(|&&x| x == 9);
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let f2 = v.par_iter().find_any(|&&x| x % 2 == 0 && x > 6);
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let f3 = v.par_iter().find_any(|&&x| x > 8);
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assert_eq!(f1, Some(&9));
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assert_eq!(f2, Some(&8));
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assert!(f3 > Some(&8));
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}
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</code></pre></pre>
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<h3 id="对数组进行并行排序"><a class="header" href="#对数组进行并行排序">对数组进行并行排序</a></h3>
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<p>下面的例子将对字符串数组进行并行排序。</p>
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<p><a href="https://docs.rs/rayon/*/rayon/slice/trait.ParallelSliceMut.html#method.par_sort_unstable">par_sort_unstable</a> 方法的排序性能往往要比<a href="https://docs.rs/rayon/1.5.1/rayon/slice/trait.ParallelSliceMut.html#method.par_sort">稳定的排序算法</a>更高。</p>
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<pre><pre class="playground"><code class="language-rust editable edition2021">use rand::{Rng, thread_rng};
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use rand::distributions::Alphanumeric;
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use rayon::prelude::*;
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fn main() {
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let mut vec = vec![String::new(); 100_000];
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// 并行生成数组中的字符串
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vec.par_iter_mut().for_each(|p| {
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let mut rng = thread_rng();
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*p = (0..5).map(|_| rng.sample(&Alphanumeric)).collect()
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});
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//
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vec.par_sort_unstable();
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}
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</code></pre></pre>
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<h3 id="并行化-map-reuduce"><a class="header" href="#并行化-map-reuduce">并行化 Map-Reuduce</a></h3>
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<p>下面例子使用 <a href="https://docs.rs/rayon/*/rayon/iter/trait.ParallelIterator.html#method.filter">rayon::filter</a>, <a href="https://docs.rs/rayon/*/rayon/iter/trait.ParallelIterator.html#method.map">rayon::map</a>, 和 <a href="https://docs.rs/rayon/*/rayon/iter/trait.ParallelIterator.html#method.reduce">rayon::reduce</a> 来超过 30 岁的 <code>Person</code> 的平均年龄。</p>
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<ul>
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<li><code>rayon::filter</code> 返回集合中所有满足给定条件的元素</li>
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<li><code>rayon::map</code> 对集合中的每一个元素执行一个操作，创建并返回新的迭代器，类似于<a href="https://course.rs/advance/functional-programing/iterator.html#%E8%BF%AD%E4%BB%A3%E5%99%A8%E9%80%82%E9%85%8D%E5%99%A8">迭代器适配器</a></li>
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<li><code>rayon::reduce</code> 则迭代器的元素进行不停的聚合运算，直到获取一个最终结果，这个结果跟例子中 <code>rayon::sum</code> 获取的结果是相同的</li>
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</ul>
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<pre><pre class="playground"><code class="language-rust editable edition2021">use rayon::prelude::*;
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struct Person {
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age: u32,
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}
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fn main() {
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let v: Vec<Person> = vec![
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Person { age: 23 },
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Person { age: 19 },
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Person { age: 42 },
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Person { age: 17 },
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Person { age: 17 },
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Person { age: 31 },
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Person { age: 30 },
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];
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let num_over_30 = v.par_iter().filter(|&x| x.age > 30).count() as f32;
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let sum_over_30 = v.par_iter()
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.map(|x| x.age)
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.filter(|&x| x > 30)
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.reduce(|| 0, |x, y| x + y);
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let alt_sum_30: u32 = v.par_iter()
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.map(|x| x.age)
|
|
.filter(|&x| x > 30)
|
|
.sum();
|
|
|
|
let avg_over_30 = sum_over_30 as f32 / num_over_30;
|
|
let alt_avg_over_30 = alt_sum_30 as f32/ num_over_30;
|
|
|
|
assert!((avg_over_30 - alt_avg_over_30).abs() < std::f32::EPSILON);
|
|
println!("The average age of people older than 30 is {}", avg_over_30);
|
|
}
|
|
</code></pre></pre>
|
|
<h3 id="并行生成缩略图"><a class="header" href="#并行生成缩略图">并行生成缩略图</a></h3>
|
|
<p>下面例子将为目录中的所有图片并行生成缩略图，然后将结果存到新的目录 <code>thumbnails</code> 中。</p>
|
|
<p><a href="https://docs.rs/glob/*/glob/fn.glob_with.html">glob::glob_with</a> 可以找出当前目录下的所有 <code>.jpg</code> 文件，<code>rayon</code> 通过 <a href="https://docs.rs/image/*/image/enum.DynamicImage.html#method.resize">DynamicImage::resize</a> 来并行调整图片的大小。</p>
|
|
<pre><pre class="playground"><code class="language-rust editable edition2021"><span class="boring">use error_chain::error_chain;
|
|
</span>
|
|
use std::path::Path;
|
|
use std::fs::create_dir_all;
|
|
|
|
<span class="boring">use error_chain::ChainedError;
|
|
</span>use glob::{glob_with, MatchOptions};
|
|
use image::{FilterType, ImageError};
|
|
use rayon::prelude::*;
|
|
|
|
<span class="boring">error_chain! {
|
|
</span><span class="boring"> foreign_links {
|
|
</span><span class="boring"> Image(ImageError);
|
|
</span><span class="boring"> Io(std::io::Error);
|
|
</span><span class="boring"> Glob(glob::PatternError);
|
|
</span><span class="boring"> }
|
|
</span><span class="boring">}
|
|
</span>
|
|
fn main() -> Result<()> {
|
|
let options: MatchOptions = Default::default();
|
|
// 找到当前目录中的所有 `jpg` 文件
|
|
let files: Vec<_> = glob_with("*.jpg", options)?
|
|
.filter_map(|x| x.ok())
|
|
.collect();
|
|
|
|
if files.len() == 0 {
|
|
error_chain::bail!("No .jpg files found in current directory");
|
|
}
|
|
|
|
let thumb_dir = "thumbnails";
|
|
create_dir_all(thumb_dir)?;
|
|
|
|
println!("Saving {} thumbnails into '{}'...", files.len(), thumb_dir);
|
|
|
|
let image_failures: Vec<_> = files
|
|
.par_iter()
|
|
.map(|path| {
|
|
make_thumbnail(path, thumb_dir, 300)
|
|
.map_err(|e| e.chain_err(|| path.display().to_string()))
|
|
})
|
|
.filter_map(|x| x.err())
|
|
.collect();
|
|
|
|
image_failures.iter().for_each(|x| println!("{}", x.display_chain()));
|
|
|
|
println!("{} thumbnails saved successfully", files.len() - image_failures.len());
|
|
Ok(())
|
|
}
|
|
|
|
fn make_thumbnail<PA, PB>(original: PA, thumb_dir: PB, longest_edge: u32) -> Result<()>
|
|
where
|
|
PA: AsRef<Path>,
|
|
PB: AsRef<Path>,
|
|
{
|
|
let img = image::open(original.as_ref())?;
|
|
let file_path = thumb_dir.as_ref().join(original);
|
|
|
|
Ok(img.resize(longest_edge, longest_edge, FilterType::Nearest)
|
|
.save(file_path)?)
|
|
}
|
|
</code></pre></pre>
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