How the single threaded non blocking IO model works in Node.js

Question

I\'m not a Node programmer, but I\'m interested in how the single threaded non blocking IO model works. After I read the article understanding-the-node-js-e

Answer 1

Okay, most things should be clear so far... the tricky part is the SQL: if it is not in reality running in another thread or process in it’s entirety, the SQL-execution has to be broken down into individual steps (by an SQL processor made for asynchronous execution!), where the non-blocking ones are executed, and the blocking ones (e.g. the sleep) actually can be transferred to the kernel (as an alarm interrupt/event) and put on the event list for the main loop.

That means, e.g. the interpretation of the SQL, etc. is done immediately, but during the wait (stored as an event to come in the future by the kernel in some kqueue, epoll, ... structure; together with the other IO operations) the main loop can do other things and eventually check if something happened of those IOs and waits.

So, to rephrase it again: the program is never (allowed to get) stuck, sleeping calls are never executed. Their duty is done by the kernel (write something, wait for something to come over the network, waiting for time to elapse) or another thread or process. – The Node process checks if at least one of those duties is finished by the kernel in the only blocking call to the OS once in each event-loop-cycle. That point is reached, when everything non-blocking is done.

Clear? :-)

I don’t know Node. But where does the c.query come from?