Improve extension API: C++ as better language for extension - Kouhei Sutou

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What I want to do
やりたいこと
Improve performance
with C/C++ libraries
C/C++のライブラリーを使った高速化
✓ Not create binding
バインディングを作りたいわけじゃない
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Point of improving perf
高速化するために大事なこと
Done in C/C++
as much as possible
できるだけC/C++内で完結させる
✓ Don't move between
C/C++ and Ruby
C/C++とRuby間でいったりきたりしない
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Example: #sum
例：#sum
numbers = (1..100000).to_a
# Move between C and Ruby: 25.1ms
numbers.inject(&:+)
# Done in C:
0.5ms
# 50x faster（50倍速い）
numbers.sum
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FYI: #inject(symbol)
参考情報：#inject(symbol)
numbers = (1..100000).to_a
# Move between C and Ruby: 25.1ms
numbers.inject(&:+)
# Done in C:
0.5ms
# 50x faster（50倍速い）
numbers.inject(:+)
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Extension and binding
拡張ライブラリーとバインディング
✓ Extension （拡張ライブラリー）
✓ Ruby library implemented in C
Cで実装されたRubyのライブラリー
✓ Binding （バインディング）
✓ Ruby library to use library
implemented in other languages
他言語実装のライブラリを使うためのRubyのライブラリ
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Binding usage
バインディングの使い方
✓ Export each API to Ruby
それぞれのAPIをRubyで使えるようにする
✓ Combine exported APIs in Ruby
バインディングが提供するAPIをRubyレベルで組み合わせる
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Binding usage example
バインディングの使い方例
require "cairo"
include Cairo
# Combine APIs
s = PDFSurface.new("red.pdf", 10, 10) # API
context = Context.new(s)
# API
context.set_source_color(:red)
# API
context.paint
# API
context.show_page
# API
s.finish
# API
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Perf improvement example
高速化例
# Don't combine APIs in Ruby
# RubyレベルでAPIを組み合わせない
## context.set_source_color(:red) # API
## context.paint
# API
## context.show_page
# API
# Just call higher level API in Ruby
# Rubyからはもっと高レベルなAPIを呼び出す
context.show_red_page # Implemented in C
# ここはCで実装
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Use case
高速化したい場面
✓ Machine learning
機械学習
✓ Combine array/matrix operations
配列・行列に対する演算をまとめる
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Raw C API for extension
拡張ライブラリー用の生のC API
Not bad but can be verbose
because of C
悪くないんだけどCなので冗長
✓ Need better approach
もっといい感じの方法を使いたい
Improve extension API - C++ as better language for extension
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Requirements
要件
✓ Easy to use C/C++ libraries
C/C++のライブラリーを簡単に使えること
✓ Easy to write
as much as possible
できるだけ書きやすいこと
✓ Easy to debug
as much as possible
できるだけデバッグしやすいこと
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Approaches （実現方法）
✓ Extend language to support
writing extension
拡張ライブラリーを書けるように言語を拡張
✓ Not based on C
C以外の言語を使う
✓ Provide convenient API
便利APIを提供
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Recommended approach
オススメの実現方法
✓ Extend language to support
writing extension
拡張ライブラリーを書けるように言語を拡張
✓ Not based on C
C以外の言語を使う
✓ Provide convenient API
便利APIを提供
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Provide convenient API
便利なAPIを提供
✓ Rice: C++ + Ruby
✓ Ext++: C++11 + Ruby
✓ Boost.Python: C++ + Python
✓ pybind11: C++11 + Python
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Useful C++ properties
C++の便利の性質
✓ C++ can use C API directory
C++ではCのAPIを直接使える
✓ No wrapper API or libffi
ラッパーAPIもlibffiもいらない
✓ C++11 or later has many
convenient features
C++11以降には便利機能がたくさんある
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C++ convenient feature1
C++の便利機能1
Type detection with "auto"
autoで型推論（C++11）
int n = 10;
auto square = n * n;
// square's type is "int"
// squareの型は「int」
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C++ convenient feature2
C++の便利機能2
Lambda expression (C++11)
ラムダ式（C++11）
// In Ruby: ->(n) {n * n}
auto square = [](int n) {
return n * n; // Return type is detected
};
square(10); // => 100
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C++ convenient feature3
C++の便利機能3
Default argument
デフォルト引数
// In Ruby: def square(n=10)
int square(int n=10) {
return n * n;
}
// square() == square(10)
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Convenient API example1
便利なAPI例1
# Ruby: Normal
class Sample
def hello
"Hello"
end
end
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Convenient API example1
便利なAPI例1
# Ruby: No syntax sugar
Sample = Class.new do
define_method(:hello) do
"Hello"
end
end
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$Convenient API example1 便利なAPI例1 // C++: Ext++ #include <ruby.hpp> extern "C" void Init_sample(void) { // Parent class (rb_cObject) is omittable rb::Class("Sample"). // class Sample in Ruby define_method("hello", // def hello in Ruby [](VALUE self) { // ->() {"Hello"} in Ruby return rb_str_new_static("Hello"); }); } Improve extension API - C++ as better language for extension Powered by Rabbit 2.2.2$ $Convenient API example1 便利なAPI例1 /* C */ #include <ruby.h> static VALUE rb_sample_hello(VALUE self) { return rb_str_new_static("Hello"); } /* ↑Definition. */ void Init_sample(void) { /* ↓Must specify parent class. */ VALUE sample = rb_define_class("Sample", rb_cObject); /* ↓Registration. They are separated. */ rb_define_method(sample, "hello", rb_sample_hello, 0); } Improve extension API - C++ as better language for extension Powered by Rabbit 2.2.2$ C++ convenient feature4
C++の便利機能4
Custom type conversion
型変換のカスタマイズ
✓ "Cast" is customizable
「キャスト」をカスタマイズできるということ
Improve extension API - C++ as better language for extension
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C++ convenient feature4
C++の便利機能4
Custom type conversion
型変換のカスタマイズ
✓ "Cast" is customizable
「キャスト」をカスタマイズできるということ
Improve extension API - C++ as better language for extension
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$Custom type conversion 型変換のカスタマイズ // Wrapper class of VALUE class Object { public: // def initialize(rb_object) // @rb_object_ = rb_object // end Object(VALUE rb_object) : rb_object_(rb_object) {} private: VALUE rb_object_; }; Improve extension API - C++ as better language for extension Powered by Rabbit 2.2.2$ $Custom type conversion 型変換のカスタマイズ class Object { operator bool() const { return RTEST(rb_object_); } }; // Object nil(Qnil); // Qnil wrapper // if (nil) { → if (RTEST(Qnil)) { Improve extension API - C++ as better language for extension Powered by Rabbit 2.2.2$ Custom type conversion
型変換のカスタマイズ
// Trap1（罠1）
// bool→int cast is available
// Implicit Object→bool→ int cast
// bool→intのキャストができるので
// 暗黙的にObject→bool→intとキャスト
Object(Qture) + 1; // → RTEST(Qtrue) + 1
// → 1 + 1
// → 2
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Custom type conversion
型変換のカスタマイズ
// Trap1（罠1）
// bool→int cast is available
// Implicit Object→bool→ int cast
// bool→intのキャストができるので
// 暗黙的にObject→bool→intとキャスト
Object(Qture) + 1; // → RTEST(Qtrue) + 1
// → 1 + 1
// → 2
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$Custom type conversion 型変換のカスタマイズ class Object { // Deny explicit cast (C++11) // 暗黙のキャストを禁止（C++11） explicit operator bool() const { return RTEST(rb_object_); } }; // Object(Qtrue) + 1; // → Compile error Improve extension API - C++ as better language for extension Powered by Rabbit 2.2.2$ $Custom type conversion 型変換のカスタマイズ // Trap2（罠2） class Object { public: // Used as implicit VALUE→Object cast // 暗黙のVALUE→Objectキャストに使われる Object(VALUE rb_object); }; Improve extension API - C++ as better language for extension Powered by Rabbit 2.2.2$ Custom type conversion
型変換のカスタマイズ
// Trap2（罠2）
// VALUE is just a number（VALUEはただの数値）
typedef unsigned long VALUE;
Object identify(Object x) {return x;}
// Implicit VALUE→Object cast
// 暗黙的にVALUE→Objectとキャスト
identify(100); // == identify(Object(100));
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Custom type conversion
型変換のカスタマイズ
// Trap2（罠2）
// VALUE is just a number（VALUEはただの数値）
typedef unsigned long VALUE;
Object identify(Object x) {return x;}
// Implicit VALUE→Object cast
// 暗黙的にVALUE→Objectとキャスト
identify(100); // == identify(Object(100));
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$Custom type conversion 型変換のカスタマイズ class Object { // Deny explicit cast // 暗黙のキャストを禁止 explicit Object(VALUE rb_object); }; // identify(100); // → Compile error Improve extension API - C++ as better language for extension Powered by Rabbit 2.2.2$ $Custom type conversion 型変換のカスタマイズ class Object { operator VALUE() const {return rb_object_;} }; // Convenient（便利） rb_p(Object(Qnil)); // → rb_p(Qnil); // Not compile error. Hmm... Object(Qnil) + 1; // → Qnil + 1; // → 8 + 1; // → 9; Improve extension API - C++ as better language for extension Powered by Rabbit 2.2.2$ C++ convenient feature5
C++の便利機能5
Template and specialization
テンプレートと特殊化
✓
Consistent cast API
一貫性のあるキャストAPIに使える
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C++ convenient feature5
C++の便利機能5
Template and specialization
テンプレートと特殊化
✓
Consistent cast API
一貫性のあるキャストAPIに使える
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$Consistent cast API 一貫性のあるキャストAPI namespace rb { // Consistent cast API // Example: rb::cast<int32_t>(Object(NUM2INT(10)); // Example: rb::cast<Object>(10); // FYI: C++ cast syntax: static_cast<TYPE>(expression) template <typename RETURN_TYPE, typename ARGUMENT_TYPE> inline RETURN_TYPE cast(ARGUMENT_TYPE object); } Improve extension API - C++ as better language for extension Powered by Rabbit 2.2.2$ $Consistent cast API 一貫性のあるキャストAPI template <> // rb::cast<int32_t>(Object(NUM2INT(10)); inline int32_t cast<int32_t, Object>(Object rb_object) { return NUM2INT(rb_object); } template <> // rb::cast<Object>(10); inline Object cast<Object, int32_t>(int32_t n) { return Object(INT2NUM(n)); } Improve extension API - C++ as better language for extension Powered by Rabbit 2.2.2$ $Consistent cast API 一貫性のあるキャストAPI // rb::cast<const char *>(Object(rb_str_new_cstr("X")); template <> inline const char *cast<const char *, Object>(Object rb_object) { VALUE rb_object_raw = rb_object; return StringValueCStr(rb_object_raw); } template <> inline // rb::cast<Object>("hello"); Object cast<Object, const char *>(const char *c_string) { return Object(rb_str_new_cstr(c_string)); } Improve extension API - C++ as better language for extension Powered by Rabbit 2.2.2$ C++ convenient feature6
C++の便利機能6
Initializer list (C++11)
初期化リスト（C++11）
✓ "{A,B,...}" is customizable
「{A, B, ...}」をカスタマイズできる
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C++ convenient feature6
C++の便利機能6
Initializer list (C++11)
初期化リスト（C++11）
✓ "{A,B,...}" is customizable
「{A, B, ...}」をカスタマイズできる
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$Initializer list 初期化リスト Object Object::send( ID name_id, std::initializer_list<VALUE> args); // Ruby: "hello".send(:tr, "e", "E") Object(rb_str_new_cstr("hello")). send(rb_intern("tr"), {rb_str_new_cstr("e"), rb_str_new_cstr("E")}); Improve extension API - C++ as better language for extension Powered by Rabbit 2.2.2$ $Initializer list 初期化リスト Object Object::send( ID name_id, std::initializer_list<VALUE> args, VALUE (*block)(VALUE data)); // Ruby: array.send(:collect) {true} Object(array). send(rb_intern("collect"), {}, // Clear API than variable arguments [](VALUE data) {return Qtrue;}); Improve extension API - C++ as better language for extension Powered by Rabbit 2.2.2$ $Convenient API example2 便利なAPI例2 // C++: Ext++ rb::Object(rb_n). send("step", // Implicit Object→VALUE cast {rb::cast<rb::Object>(10)}, [](VALUE i) {return rb_p(i)}); // n.step(10) {|i| p i} Improve extension API - C++ as better language for extension Powered by Rabbit 2.2.2$ $Convenient API example3 便利なAPI例3 // C++: Rice #include <rice/Class.hpp> static const char * // Not VALUE! (Auto convert) rb_sample_hello(Rice::Object self) { return "Hello"; } extern "C" void Init_sample() { Rice::define_class("Sample"). define_method("hello", &rb_sample_hello); } Improve extension API - C++ as better language for extension Powered by Rabbit 2.2.2$ C++ based API: Pros1
C++ベースのAPI：長所1
Easier to write than C
Cより書きやすい
✓ Require C++11 or later
C++11以降なら
Improve extension API - C++ as better language for extension
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C++ based API: Pros1
C++ベースのAPI：長所1
Easier to write than C
Cより書きやすい
✓ Require C++11 or later
C++11以降なら
Improve extension API - C++ as better language for extension
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C++ based API: Pros2
C++ベースのAPI：長所2
Easy to use for C API users
既存のC APIを使っている人なら使いやすい
✓ Use C directly incl macro
マクロも含めてCの機能を直接使える
✓ Don't need to migrate to all
convenient API at once
一気に書き換えるのではなく徐々に移行できる
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C++ based API: Pros3
C++ベースのAPI：長所3
Easy to debug for C API users
既存のC APIを使っている人ならデバッグしやすい
✓ Can use GDB/LLDB directly
GDB/LLDBを直接使える
✓ GDB/LLDB have built-in C++ support
GDB/LLDBは組み込みでC++をサポート
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C++ based API: Pros4
C++ベースのAPI：長所4
Easy to optimize
最適化しやすい
✓ [Feature #13434] better
method definition in C API
Cのメソッド定義APIの改良
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Better method definition
メソッド定義の改良
✓ Metadata for optimization
最適化のためにメタデータを付与
✓ e.g.: Reduce memory allocations
例：メモリーアロケーションを減らす
✓ Lazy method definition
必要になるまでメソッド定義を遅らせる
✓ e.g.: Reduce start-up time
例：起動時間の高速化
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Argument metadata
引数のメタデータ
class Hello
# Default argument is just for
# example. Other metadata will
# be more useful for optimization.
def hello(name, message="world")
end
end
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Argument metadata
引数のメタデータ
// C++: Rice
cHello.
define_method(
"hello",
&hello,
(Rice::Arg("name"), // ↓Default
Rice::Arg("message")="world"));
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Lazy method definition
遅延メソッド定義
class X
def a; end # Not define yet
def b; end # Not define yet
end
x = X.new
x.a # Define #a and #b
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$Lazy method definition 遅延メソッド定義 /* One of new C API ideas */ struct rb_method_entries entries[] = { "a", ..., "b", ..., }; /* The definitions aren't defined at once. */ /* They are defined when the next method call. */ rb_define_method_with_table(rb_cX, entries); Improve extension API - C++ as better language for extension Powered by Rabbit 2.2.2$ $Lazy method definition 遅延メソッド定義 // C++ implementation sample { rb::Class("X"). // Don't call rb_define_method() yet. define_method("a", ...). // Don't call rb_define_method() yet. define_method("b", ...); // Destructor is called. // Call rb_define_method_with_table() // in destructor. } Improve extension API - C++ as better language for extension Powered by Rabbit 2.2.2$

Lazy method definition
遅延メソッド定義
// Ext++ implementation is just for test
rb::Class("X").
// Call rb_define_method() immediately.
define_method("a", ...).
// Don't call rb_define_method() in
// the following define_method()s.
enable_lazy_define_method().
// Don't call rb_define_method() yet.
define_method("b", ...);
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$Lazy method definition 遅延メソッド定義 # Define only benchmark code in Ruby. # Benchmark target code is in C++. n = 10000 Bench = Class.new do n.times do |i| define_method("method#{i}") do end end end Improve extension API - C++ as better language for extension Powered by Rabbit 2.2.2$ $Lazy method definition 遅延メソッド定義 # Call benchmark code in Ruby. # Benchmark target code is in C++. n = 10000 bench = Bench.new n.times do |i| bench.__send__("method#{i}") end Improve extension API - C++ as better language for extension Powered by Rabbit 2.2.2$ Lazy method definition
遅延メソッド定義
Type
Normal
Lazy
Define only
5ms
1ms
Called
5ms
5ms
5x faster when any methods
aren't called
メソッドが呼ばれなければ5倍速い
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Lazy method definition
遅延メソッド定義
Type
Normal
Lazy
Define only
5ms
1ms
Called
5ms
5ms
5x faster when any methods
aren't called
メソッドが呼ばれなければ5倍速い
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C++ based API: Cons1
C++ベースのAPI：短所1
C++ is difficult
C++は難しい
✓ e.g.: Template
たとえばテンプレート
✓ Easy to write unreadable code
簡単にリーダブルじゃないコードを書ける
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C++ based API: Cons2
C++ベースのAPI：短所2
Slower build
ビルドが遅い
✓ It may reduce try&error cycle
試行錯誤しにくくなるかも
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C++ based API: Problem
C++ベースのAPI：課題
Exception
例外
✓ Ruby exception breaks C++
RAII (destructor)
(Resource Acquisition Is Initialization)
Rubyの例外発生→C++のRAII（デストラクター）が動かない
✓ Because it uses setjmp/longjmp
Rubyの例外はsetjmp/longjmpを使っているから
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Exception: Solution
例外：解決法
1. Rescue Ruby exception
Rubyの例外をrescue
2. Throw C++ exception
C++の例外にしてthrow
3. Re-raise the Ruby exception
安全な場所でRubyの例外を再raise
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Conclusion
まとめ
✓ C++ based API is useful
C++ベースのAPIは便利
✓ For writing ext uses C/C++ library
C/C++のライブラリを使う拡張ライブラリを書くとき
✓ For optimizing w/ easy to use API
例：使いやすいAPIを維持したまま最適化するとき
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Appendix
付録
Introduce easy to write
extension approaches
拡張ライブラリーを簡単に実装する方法を紹介
✓ The following contents are
used only when time is
remained
以降の内容は時間が残っている場合だけ使う
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Extend language
言語を拡張
✓ Rubex: Extended Ruby
Rubex：Rubyを拡張
✓ Cython: Extended Python
Cython：Pythonを拡張
Improve extension API - C++ as better language for extension
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How to run
動かし方
✓ Translate extension code to C
拡張言語で書かれたコードをCにコンパイル
✓ Compile C code
コンパイルされたCコードをビルド
✓ Load the built extension
ビルドした拡張ライブラリーを読み込む
Improve extension API - C++ as better language for extension
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Extended syntax
拡張された構文
✓ Type information
型情報を書ける
✓ C code snippet
Cのコードを書ける
Improve extension API - C++ as better language for extension
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How to run: Rubex
Rubexの動かし方
# fibonacci.rubex
class Fibonacci
# "int" is type information
def compute(int n)
# ...
end
end
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How to run: Rubex
Rubexの動かし方
%
%
%
%
rubex fibonacci.rubex
cd fibonacci
ruby extconf.rb
make
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How to run: Rubex
Rubexの動かし方
require_relative "fibonacci.so"
p Fibonacci.new.compute(100)
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Extend language: Pros1
拡張言語：長所1
Friendly syntax for
base language users
ベースの言語のユーザーにはなじみやすい構文
✓ Most syntax is the same
構文の大部分は同じだから
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Extend language: Pros2
拡張言語：長所2
Easy to migrate from base lang
ベースの言語からの移行が容易
✓ Because upward compatibility
上位互換だから
✓ Code for base language works
without modification
ベースの言語で書かれたコードは変更なしで動く
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Extend language: Pros3
拡張言語：長所3
Doesn't require much C knowledge
そんなにCの知識は必要ない
✓ Most code can be written with
base language knowledge
コードの大部分はベースの言語の知識で書ける
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Extend language: Cons1
拡張言語：短所1
You realize that it's not
friendly syntax when you use it
使うとそんなになじみやすい文法ではないと気づく
✓ Small differences will
confuse you
小さな違いがいろいろあってわかりにくい
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Extend language: Cons2
拡張言語：短所2
Difficult to debug
デバッグが難しい
✓ Need base language, extend
language and C knowledge
ベースの言語の知識も拡張言語の知識もCの知識も必要
Cython has GDB integration to solve this problem
Cythonはこの問題を解決するためにGDB用の便利機能を提供
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Extend language: Cons3
拡張言語：短所2
Hard to maintain
(For maintainers, not for users)
（ユーザーではなくメンテナーが）メンテナンスが大変
✓ Base language introduces a
new syntax then extend
language should implement it
ベースの言語が新しい構文を導入→拡張言語でも実装
Improve extension API - C++ as better language for extension
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Not based on C
C言語以外をベースにする
✓ JRuby: Java + Ruby
✓ Helix: Rust + Ruby
Improve extension API - C++ as better language for extension
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How to run: JRuby
JRubyでの動かし方
// Fibonacci.java
public class Fibonacci {
public long[] compute(int n) {
// ...
}
}
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How to run: JRuby
JRubyでの動かし方
% javac Fibonacci.java
% jar cf fibonacci.jar Fibonacci.class
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How to run: JRuby
JRubyでの動かし方
require "fibonacci.jar"
java_import "Fibonacci"
p Fibonacci.new.compute(100)
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Not based on C: Pros1
C言語以外をベースにする：長所1
Easier to write than C
Cより書きやすい
✓ Simpler syntax
洗練された構文
✓ Rich features compared to C
Cより機能が多い
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Not based on C: Pros2
C言語以外をベースにする：長所2
Can use libraries
in base language
ベース言語のライブラリーを使える
✓ Major languages have many libs
広く使われている言語はライブラリーも多い
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Not based on C: Cons1
C言語以外をベースにする：短所1
Need base language knowledge
ベース言語の知識が必要
✓ Java for JRuby （JRubyならJava）
✓ Rust for Helix （HelixならRust）
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Not based on C: Cons2
C言語以外をベースにする：短所2
May need C knowledge
(When Ruby implementation is MRI)
Rubyの実装がMRIならCの知識が必要かもしれない
✓ Base language wraps Ruby C API
ベースの言語はRubyのC APIをラップしている
✓ e.g.: sys::RSTRING_PTR on Helix
例：Helixならsys::RSTRING_PTRがラップしたAPI
Improve extension API - C++ as better language for extension
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Not based on C: Cons3
C言語以外をベースにする：短所3
Hard to maintain
(When Ruby implementation is MRI)
Rubyの実装がMRIならメンテナンスが大変かも
✓ Ruby introduces a new API
then base language may need
to implement it
Rubyが新しいAPIを追加→ベース言語でも実装？
✓ e.g.: rb_gc_adjust_memory_usage()
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$How to run: Rice Riceの動かし方 #include <rice/Class.hpp> static const char * // Not VALUE! rb_sample_hello(Rice::Object self) { return "Hello"; } extern "C" void Init_sample() { Rice::define_class("Sample"). define_method("hello", &rb_sample_hello); } Improve extension API - C++ as better language for extension Powered by Rabbit 2.2.2$ How to run: Rice
Riceの動かし方
# extconf.rb
require "mkmf-rice"
create_makefile("sample")
Improve extension API - C++ as better language for extension
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How to run: Rice
Riceの動かし方
# extconf.rb
require "mkmf-rice"
create_makefile("sample")
Improve extension API - C++ as better language for extension
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How to run: Rice
Riceの動かし方
% ruby extconf.rb
% make
Improve extension API - C++ as better language for extension
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How to run: Rice
Riceの動かし方
require_relative "sample.so"
p Sample.new.hello
# => "Hello"
Improve extension API - C++ as better language for extension
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Provide C++ API: Pros
C++ APIを提供：長所
Omit
省略
Improve extension API - C++ as better language for extension
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Provide C++ API: Cons
C++ APIを提供：短所
Omit
省略
Improve extension API - C++ as better language for extension
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Provide C++ API: ConsN
C++ APIを提供：短所N
Conv from Ruby may be a bother
Ruby実装の移植が面倒
✓ C++ with convenient Ruby C
API needs more code than Ruby
RubyのC APIにC++の便利APIがあっても
Rubyよりもたくさんコードが必要
Improve extension API - C++ as better language for extension
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From Ruby: Rice
RubyからRiceに移植
def fib(n)
prev = 1
current = 1
1.step(n - 1).collect do
prev, current = current, current + prev
prev
end
end
Improve extension API - C++ as better language for extension
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$From Ruby: Rice RubyからRiceに移植 std::vector<uint64_t> fib(Rice::Object self, int n) { uint64_t prev = 1, current = 1; std::vector<uint64_t> numbers; for (int i = 1; i < n; ++i) { auto temp = current; current += prev; prev = temp; numbers.push_back(prev); } return numbers; } Improve extension API - C++ as better language for extension Powered by Rabbit 2.2.2$