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
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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.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.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.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.
3.3
非同期パターン（
async
ライブラリ編）
71
3.3.3
同時実行数を制限した並行処理パターン
最後になりますが、
async
には並行処理の同時実行数を制御する機能はあるのでしょうか。答えは
Yes
です。
eachLimit()
、
mapLimit()
、
parallelLimit()
、
queue()
、そして
cargo()
がその目
的に使えます。
ここでは、バージョン
4
のウェブスパイダーを
async.queue()
を使って書き換えます。
async.
queue()
は我々の実装した
TaskQueue
クラスと似ており、関数
worker()
と、タスク数の上限値であ
る
concurrency
を引数として取り、キューのインスタンスを生成します。
const q = async.queue(worker, concurrency);
関数
worker()
は次のシグニチャをもちます。この関数はタスクおよび処理完了時に呼び出すコー
ルバックを引数として受け取ります。
function worker(task, callback)
ここで
task
は特に関数である必要はなく、関数
worker()
が扱える形式であれば何でもかまいませ
ん。また、新しいタスクは
q.push(task, callback)
で追加できます。ここで渡しているコールバッ
クは
worker()
により、タスクが完了した際に呼び出されます。
では、実際にバージョン
4
のウェブスパイダーを、
async.queue()
を使って書き換えてみましょう。
まず、次のように
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Read now
Unlock full access
More than 5,000 organizations count on O’Reilly
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.