foreyez foreyez - 28 days ago 4
Node.js Question

Why is Node.js single threaded?

In PHP (or Java/ASP.NET/Ruby) based webservers every client request is instantiated on a new thread. But in Node.js all the clients run on the same thread (they can even share the same variables!) I understand that I/O operations are event based so they don't block the main thread loop.

What I don't understand is WHY the author of Node chose it to be single threaded? It makes things difficult. For example I can't run a CPU intensive function because it blocks the main thread (and new client requests are blocked) so I need to spawn a process (which means I need to create a separate JavaScript file and execute another node process on it). However in PHP cpu intensive tasks do not block other clients because as I mentioned each client is on a different thread. What are its advantages compared to multi-threaded web servers?

Note: I've used clustering to get around this, but it's not pretty.

Answer

Node.js was created explicitly as an experiment in async processing. The theory was that doing async processing on a single thread could provide more performance and scalability under typical web loads than the typical thread-based implementation.

And you know what? In my opinion that theory's been borne out. A node.js app that isn't doing CPU intensive stuff can run thousands more concurrent connections than Apache or IIS or other thread-based servers.

The single threaded, async nature does make things complicated. But do you honestly think it's more complicated than threading? One race condition can ruin your entire month! Or empty out your thread pool due to some setting somewhere and watch your response time slow to a crawl! Not to mention deadlocks, priority inversions, and all the other gyrations that go with multithreading.

In the end, I don't think it's universally better or worse; it's different, and sometimes it's better and sometimes it's not. Use the right tool for the job.

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