Is uWebSockets single threaded?

[mrinvicto]

Node.js is single threaded, but since uWebSockets is written in c/c++ is it still single threaded?

[Jacob-Burckhardt]

Yes.

https://github.com/uNetworking/uWebSockets/blob/master/misc/READMORE.md#threading

says:

The library is single threaded. You cannot, absolutely not, mix threads. A socket created from an App on thread 1 cannot be used in any way from thread 2. The only function in the whole entire library which is thread-safe and can be used from any thread is Loop:defer. Loop::defer takes a function (such as a lambda with data) and defers the execution of said function until the specified loop's thread is ready to execute the function in a single-threaded fashion on correct thread. So in case you want to publish a message under a topic, or send on some other thread's sockets you can, but it requires a bit of indirection. You should aim for having as isolated apps and threads as possible.

That page has some other helpful mentions of the word "thread".