NodeJS: Who does the asynchronous work when a async function is called?

Question

I will explain my question with example.

fs.readFile('somefilename', function(err, data) {
    ...doSomething...
});

When this line of code is executed readFile will start reading the file. On success or failure this callback will be pushed into queue for execution with appropriate arguments.

Reading of file is happening asynchronously, but who's doing it if NodeJS is single threaded, non-blocking?

Answer 1

User code is executed in a single thread. However, behind the scenes nodejs uses libuv/libio to handle any io which does use threads.

https://github.com/libuv/libuv

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