May 2019
Intermediate to advanced
464 pages
9h 22m
Japanese
Content preview from Node.jsデザインパターン 第2版
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5.3
非同期プログラミングにおけるストリームの活用
127
関数
concatFiles()
によって、ストリームだけを使って非同期の逐次的イテレーションが可能に
なったわけです。
3
章で見たように、
ES6
以前の
JavaScript
ならばイテレータが必要だったところです
（
ES2015
あるいは
async
ライブラリなどが必要）。コンパクトかつエレガントな別の方法で同じ効果を
得ることができたわけです。
パターン
ストリームを組み合わせることで、一群の非同期タスクのイテレーションを簡潔に記述で
きる。
5.3.2
順序なしの並行実行
データチャンクを順に処理するのにストリームを使うことができますが、このような処理は
Node
の
並列性を有効に利用しておらず、ボトルネックになる場合があります。各データチャンクに対して遅い
非同期の操作を実行しなければならないとすると、
Paralle
ストリームを使って実行を並行化し全体の
処理速度を上げたほうがよいことになります。もちろん、この操作はデータの各チャンクの間の関係が
ない場合に限り可能になります（オブジェクトストリームに対してはこのようなケースが多いでしょう
が、バイナリストリームに関しては稀でしょう）。
Parallel
ストリームはデータが処理される順番に意味がある場合は使えません。
Transform
ストリームの実行を並行化するには、
3
章で見たのと同じようなパターンを適用できます
（少し変更が必要です）。
5.3.2.1
順序なし
Parallel
ストリームの実装
例を見ま ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.