Question

我需要在单个线程中编写Clojure中的merge-sort算法的实现，并使用带有2,4,8,16和32个线程的并行选项。
程序将从文本文件中读取大量整数（100万），并将它们放入列表中进行排序我是Clojure和函数式编程的新手。
我刚刚编写了阅读文件的代码......

(use 'clojure.java.io)
(defn get-lines [fname]
  (with-open [r (reader fname)]
    (doall (map read-string (line-seq r)))))
(def numbers (get-lines "numbers.dat"))

...找到单线程实现。
但我无法实现并行算法。这似乎超出了我的范围有人能帮助我吗？

Answer 1

如果有人在寻找......

(use 'clojure.java.io)

(defn get-lines [fname]
  (with-open [r (reader fname)]
    (doall (map read-string (line-seq r)))))

(def numbers (get-lines "numbers.dat"))

(defn merge-lists [left right]
  (loop [head [] L left R right]
    (if (empty? L) (concat head R)
    (if (empty? R) (concat head L)
    (if (> (first L) (first R))
      (recur (conj head (first R)) L (rest R))
      (recur (conj head (first L)) (rest L) R))))))

(defn naive-merge-sort [list]
  (if (< (count list) 2) list
    (apply merge-lists
      (map naive-merge-sort
        (split-at (/ (count list) 2) list)))))

(defn parallel-merge-sort-2 [list]
  (if (< (count list) 2) list
    (apply merge-lists
      (pmap naive-merge-sort
        (split-at (/ (count list) 2) list)))))

(defn parallel-merge-sort-4 [list]
  (if (< (count list) 2) list
    (apply merge-lists
      (pmap parallel-merge-sort-2
        (split-at (/ (count list) 2) list)))))

(defn parallel-merge-sort-8 [list]
  (if (< (count list) 2) list
    (apply merge-lists
      (pmap parallel-merge-sort-4
        (split-at (/ (count list) 2) list)))))

(defn parallel-merge-sort-16 [list]
  (if (< (count list) 2) list
    (apply merge-lists
      (pmap parallel-merge-sort-8
        (split-at (/ (count list) 2) list)))))

(defn parallel-merge-sort-32 [list]
  (if (< (count list) 2) list
    (apply merge-lists
      (pmap parallel-merge-sort-16
        (split-at (/ (count list) 2) list)))))

naive-merge-sort是单线程实现。并行实现将输入列表分成2-32个块，这些块使用naive-merge-sort进行排序。

Answer 2

这听起来很像家庭作业（如评论者所说），所以我对提供详细答案犹豫不决。我可以告诉你，你想要在Clojure中研究不同类型的并发性。从最简单到最复杂的顺序，您可能要考虑的一些方法是pmap，futures和core.async。我建议您查看basic docs for pmap， Clojure For the Brave and True 的章节concurrency和core.async以及clojure。 org＆＃39; page about concurrency

Clojure中的多线程合并排序算法

2 个答案: