Question is − how Node.js process multiple http or any other requests and there can be question on performance, security as well?
Node.js starts event loop on application start and handles callback functions using it.Node.js maintains a worker pool. Long running operations are transferred to this worker pool and event pool only handles responses from this worker pool on completion of tasks.
Worker pool works with operating system to do the heavy lifting of work and managing scheduling of tasks.
Worker pool once finished task responds to event loop using callback functions.
Event loop maintains the order of execution for appropriate events.
Event loop −
It first checks for any timer events like setTimeout or setInterval.
Second, it checks for pending callbacks e.g. I/O related callbacks pending to execute.
Next step is Poll; Node will try to find new I/O for executing their callback functions.
Check phase, in this phase node will execute callback functions immediately. It uses setImmediate call
Close callback − In the end node will do the close callback functions which are registered.
If there are no registered events remaining for execution then only node will do process.exit .
Node maintains a ref variable to hold the counter for events, on each new event the counter will get incremented.
In server environment, we create a server using createServer which does not have a close event so it won’t get closed automatically by node.js unless process is stopped by manually.
By default node mainatsn scopes for each http request to avoid it from being mixed with other requests.
The global objects defined if any can be accessed by any requests and that requires to be taken care by developer.