在 JRuby 中使用带有 c 扩展的 gem，或者将它们移植到 Java？答案

【问题标题】：Use gems with c-extensions in JRuby, or port them to Java?在 JRuby 中使用带有 c 扩展的 gem，或者将它们移植到 Java？
【发布时间】：2016-09-03 22:25:14
【问题描述】：

我正在对输入字符串和一些以前输入的字符串进行模糊匹配测试。测试是在打字时实时进行的。

我已经有了一个非常准确的算法，叫做StrikeAMatch，它是has been translated into many languages。我发现最快的 Ruby 实现是amatch。但是，它与我的 JRuby 环境 because it crunches data in a C extension 不兼容，后者需要 C 语言解释器 (MRI)。不过速度很快：

a = "Lorem ipsum dolor"
b = "Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Nam cursus. Morbi ut mi. Nullam enim leo, egestas id, condimentum at, laoreet mattis, massa. Sed eleifend nonummy diam. Praesent mauris ante,"
puts Benchmark.measure {
  10000.times { a.pair_distance_similar(b) }
}
# => 0.130000   0.000000   0.130000 (  0.146347)

我希望我可以避免设置替代环境。另一种方法是尝试移植原始 Java 代码as suggested in the JRuby Wiki。不过不知道该怎么做。

关于如何解决这个问题的任何想法？

【问题讨论】：

标签： jruby fuzzy-search ruby-c-extension jruby-java-interop mri

【解决方案1】：

有两种方法可以解决这个问题：

从现有的 Ruby gem 中获取 C ext 代码并将其移植到 Java

... 有许多 gem 的示例具有 C-Ruby/JRuby 的特定扩展，例如 json/nokogiri

获取 Java 端口，加载 Java 类并使用 JRuby 的 Java 集成

【讨论】：

【解决方案2】：

该算法易于实现。例如，这是我用 Java 编写的一个快速实现：

import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

public class StrikeAMatch {

    protected int numPairs(final String string) {
        return Math.max(0, string.length() - 1);
    }

    protected Map<String, Integer> pairs(final String string) {
        if (string.isEmpty()) {
            return new HashMap<>(0);
        }

        final Map<String, Integer> pairs = new HashMap(2 * numPairs(string));

        for (int i = 1, j = string.length(); i < j; i += 1) {
            final char a = string.charAt(i - 1);
            final char b = string.charAt(i);
            final String pair = String.format("%c%c", a, b);
            if (pairs.containsKey(pair)) {
                pairs.put(pair, 1 + pairs.get(pair));
            }
            else {
                pairs.put(pair, 1);
            }
        }

        return pairs;
    }

    protected int intersectionSize(
            final Map<String, Integer> lhsPairs,
            final Map<String, Integer> rhsPairs) {
        final Set<String> lhsKeys = lhsPairs.keySet();
        final Set<String> rhsKeys = rhsPairs.keySet();
        final Set<String> pairIntersection = new HashSet<>(lhsKeys);
        pairIntersection.retainAll(rhsKeys);
        int sharedPairs = 0;
        for (final String pair : pairIntersection) {
            sharedPairs += Math.min(lhsPairs.get(pair), rhsPairs.get(pair));
        }
        return sharedPairs;
    }

    public double between(final String lhs, final String rhs) {
        if (lhs.isEmpty() && rhs.isEmpty()) {
            return 1.0;
        }
        final Map<String, Integer> lhsPairs = pairs(lhs.toUpperCase());
        final Map<String, Integer> rhsPairs = pairs(rhs.toUpperCase());
        return (2.0 * intersectionSize(lhsPairs, rhsPairs))
             / (numPairs(lhs) + numPairs(rhs));
    }

    public static void main(final String[] args) {
        final StrikeAMatch distance = new StrikeAMatch();
        for (final String lhs : args) {
            for (final String rhs : args) {
                System.out.printf("d(\"%s\", \"%s\") = [%.7f]%n",
                    lhs, rhs, distance.between(lhs, rhs));
            }
        }
    }
}

您甚至可以填充第一个和最后一个字符，以将其扩展到一个字符或零个字符的术语：

import java.util.HashMap;
import java.util.Map;

public class PaddedStrikeAMatch extends StrikeAMatch {

    protected int numPairs(final String string) {
        return string.length() + 1;
    }

    protected Map<String, Integer> pairs(final String string) {
        if (string.isEmpty()) {
            final Map<String, Integer> pairs = new HashMap<>(1);
            pairs.put("  ", 1);
            return pairs;
        }

        final Map<String, Integer> pairs = new HashMap(2 * numPairs(string));
        pairs.put(String.format(" %c", string.charAt(0)), 1);
        pairs.put(String.format("%c ", string.charAt(string.length() - 1)), 1);

        for (int i = 1, j = string.length(); i < j; i += 1) {
            final char a = string.charAt(i - 1);
            final char b = string.charAt(i);
            final String pair = String.format("%c%c", a, b);
            if (pairs.containsKey(pair)) {
                pairs.put(pair, 1 + pairs.get(pair));
            }
            else {
                pairs.put(pair, 1);
            }
        }

        return pairs;
    }

    public static void main(final String[] args) {
        final StrikeAMatch distance = new PaddedStrikeAMatch();
        for (final String lhs : args) {
            for (final String rhs : args) {
                System.out.printf("d(\"%s\", \"%s\") = [%.7f]%n",
                    lhs, rhs, distance.between(lhs, rhs));
            }
        }
    }
}

为了验证它，以下是您提供的链接中提出的示例：

% java StrikeAMatch France French
d("France", "France") = [1.0000000]
d("France", "French") = [0.4000000]
d("French", "France") = [0.4000000]
d("French", "French") = [1.0000000]

% java StrikeAMatch Healed Sealed Healthy Heard Herded Help Sold
d("Healed", "Healed") = [1.0000000]
d("Healed", "Sealed") = [0.8000000]
d("Healed", "Healthy") = [0.5454545]
d("Healed", "Heard") = [0.4444444]
d("Healed", "Herded") = [0.4000000]
d("Healed", "Help") = [0.2500000]
d("Healed", "Sold") = [0.0000000]
d("Sealed", "Healed") = [0.8000000]
d("Sealed", "Sealed") = [1.0000000]
d("Sealed", "Healthy") = [0.3636364]
d("Sealed", "Heard") = [0.2222222]
d("Sealed", "Herded") = [0.2000000]
d("Sealed", "Help") = [0.0000000]
d("Sealed", "Sold") = [0.0000000]
d("Healthy", "Healed") = [0.5454545]
d("Healthy", "Sealed") = [0.3636364]
d("Healthy", "Healthy") = [1.0000000]
d("Healthy", "Heard") = [0.4000000]
d("Healthy", "Herded") = [0.1818182]
d("Healthy", "Help") = [0.2222222]
d("Healthy", "Sold") = [0.0000000]
d("Heard", "Healed") = [0.4444444]
d("Heard", "Sealed") = [0.2222222]
d("Heard", "Healthy") = [0.4000000]
d("Heard", "Heard") = [1.0000000]
d("Heard", "Herded") = [0.4444444]
d("Heard", "Help") = [0.2857143]
d("Heard", "Sold") = [0.0000000]
d("Herded", "Healed") = [0.4000000]
d("Herded", "Sealed") = [0.2000000]
d("Herded", "Healthy") = [0.1818182]
d("Herded", "Heard") = [0.4444444]
d("Herded", "Herded") = [1.0000000]
d("Herded", "Help") = [0.2500000]
d("Herded", "Sold") = [0.0000000]
d("Help", "Healed") = [0.2500000]
d("Help", "Sealed") = [0.0000000]
d("Help", "Healthy") = [0.2222222]
d("Help", "Heard") = [0.2857143]
d("Help", "Herded") = [0.2500000]
d("Help", "Help") = [1.0000000]
d("Help", "Sold") = [0.0000000]
d("Sold", "Healed") = [0.0000000]
d("Sold", "Sealed") = [0.0000000]
d("Sold", "Healthy") = [0.0000000]
d("Sold", "Heard") = [0.0000000]
d("Sold", "Herded") = [0.0000000]
d("Sold", "Help") = [0.0000000]
d("Sold", "Sold") = [1.0000000]

...这是填充版本：

% java PaddedStrikeAMatch France French
d("France", "France") = [1.0000000]
d("France", "French") = [0.4285714]
d("French", "France") = [0.4285714]
d("French", "French") = [1.0000000]

% java PaddedStrikeAMatch Healed Sealed Healthy Heard Herded Help Sold
d("Healed", "Healed") = [1.0000000]
d("Healed", "Sealed") = [0.7142857]
d("Healed", "Healthy") = [0.5333333]
d("Healed", "Heard") = [0.6153846]
d("Healed", "Herded") = [0.5714286]
d("Healed", "Help") = [0.3333333]
d("Healed", "Sold") = [0.1666667]
d("Sealed", "Healed") = [0.7142857]
d("Sealed", "Sealed") = [1.0000000]
d("Sealed", "Healthy") = [0.2666667]
d("Sealed", "Heard") = [0.3076923]
d("Sealed", "Herded") = [0.2857143]
d("Sealed", "Help") = [0.0000000]
d("Sealed", "Sold") = [0.3333333]
d("Healthy", "Healed") = [0.5333333]
d("Healthy", "Sealed") = [0.2666667]
d("Healthy", "Healthy") = [1.0000000]
d("Healthy", "Heard") = [0.4285714]
d("Healthy", "Herded") = [0.2666667]
d("Healthy", "Help") = [0.3076923]
d("Healthy", "Sold") = [0.0000000]
d("Heard", "Healed") = [0.6153846]
d("Heard", "Sealed") = [0.3076923]
d("Heard", "Healthy") = [0.4285714]
d("Heard", "Heard") = [1.0000000]
d("Heard", "Herded") = [0.6153846]
d("Heard", "Help") = [0.3636364]
d("Heard", "Sold") = [0.1818182]
d("Herded", "Healed") = [0.5714286]
d("Herded", "Sealed") = [0.2857143]
d("Herded", "Healthy") = [0.2666667]
d("Herded", "Heard") = [0.6153846]
d("Herded", "Herded") = [1.0000000]
d("Herded", "Help") = [0.3333333]
d("Herded", "Sold") = [0.1666667]
d("Help", "Healed") = [0.3333333]
d("Help", "Sealed") = [0.0000000]
d("Help", "Healthy") = [0.3076923]
d("Help", "Heard") = [0.3636364]
d("Help", "Herded") = [0.3333333]
d("Help", "Help") = [1.0000000]
d("Help", "Sold") = [0.0000000]
d("Sold", "Healed") = [0.1666667]
d("Sold", "Sealed") = [0.3333333]
d("Sold", "Healthy") = [0.0000000]
d("Sold", "Heard") = [0.1818182]
d("Sold", "Herded") = [0.1666667]
d("Sold", "Help") = [0.0000000]
d("Sold", "Sold") = [1.0000000]

如果您想直接从 JRuby 中使用它，您只需将 StrikeAMatch.class 添加到您的 $CLASSPATH，并在您的脚本中添加 require 'java' 后跟 java_import 'StrikeAMatch：

require 'java'

java_import 'StrikeAMatch'

distance = StrikeAMatch.new
ARGV.each do |lhs|
  ARGV.each do |rhs|
    puts "d(\"#{lhs}\", \"#{rhs}\") = [#{distance.between(lhs, rhs)}]"
  end
end

调用它：

% jruby strike_a_match.rb France French
d("France", "France") = [1.0]
d("France", "French") = [0.4]
d("French", "France") = [0.4]
d("French", "French") = [1.0]

【讨论】：

我无语了，感谢您提供如此详尽的回答。我将在接下来的几天里尝试实施它。在速度方面，您认为这个 Java 实现与 C 实现相比如何？我可以看出 pure Ruby implementation 比 amatch C 实现慢 17 倍，所以显然执行字符串测试的语言有很大的不同。
大部分性能差异将归因于库对算法和数据结构的选择。其中一些还与原语与对象有关，因为 Ruby 没有原语，所以你的字符等都是装箱的（你不选择 Ruby 来获得原始性能）。我在映射值中编写了整数框的实现，因此您可能想要查看 fastutil，它具有映射到原始整数的 Object2IntMap 类型。如果您想要原始速度，还有很大的优化空间。稍后我将比较 C 和 Ruby 的实现。