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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58
3
章 コールバックを用いた非同期パターン
3.2.4
並行処理
複数の非同期処理を実行する際に、処理の順番は特に重要ではなく、すべての処理が完了した際に
通知してくれさえすればそれで事足りる場合があります。そのような場合には逐次処理である必要は
なく、すべてのタスクを並行に実行するほうがよいでしょう（図3-2）。
開始
タスク
1
タスク
2
タスク
3
終了
図3-2 並行処理
Node
はシングルスレッドアーキテクチャなのに、どうやってタスクを並行処理するのでしょうか。
これに関しては、
1
章で説明したとおり、
Node
はそのノンブロッキング
API
のおかげで、単一のスレッ
ドでも並行性を実現できます。実際にはタスクは同時に処理されるわけではなく、イベントループによ
りインタリーブ
＊
1
される形で複数のタスクが交互に実行されます。
1
章で詳しく見たとおり、あるタスク内で非同期処理が実行されると、いったんイベントループに制
御が戻り、別のタスクのイベントが実行されます。そういう意味では、あくまでも並行処理（
concurrent
processing
。論理的に、順 不同にあるいは同時に起こりうる処理 ）であって並 列処 理（
parallel
processing
。複数の
CPU
で同時に処理を行う）ではありません。
図3-3は
Node
のアプリケーションで
2
つの非
同期タスクが並行処理される様子を表したものです。
＊
1 interleave
は「 交 互 に 挿 入 する」「本に白 紙 を挟 み 込 む 」などの意味をもつ言葉。 ...
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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.