Concurrency in Node.js is primarily achieved through the use of the event loop and non-blocking I/O operations. Despite JavaScript being single-threaded, Node.js can perform non-blocking tasks by offloading operations to the system kernel whenever possible. Since most modern kernels are multi-threaded, they can handle multiple operations executing in the background. When one of these operations completes, the kernel informs Node.js so that the appropriate callback may be added to the poll queue and eventually executed by the event loop[5].
The event loop is a loop that runs as long as the Node.js application is running. It has several queues for different types of tasks, and it processes these tasks in a specific order. The event loop allows Node.js to perform I/O operations asynchronously, which means that the system can continue to handle other tasks while waiting for I/O operations to complete[1].
Node.js also provides the option to use worker threads for CPU-intensive tasks. Worker threads are separate threads that can run alongside the main thread, allowing for parallel execution of JavaScript code. This feature was introduced as an experimental feature in Node.js version 10 and became stable in version 12. Worker threads allow Node.js to perform CPU-intensive computations without blocking the main event loop, thus enabling concurrent processing[2][3].
In summary, concurrency in Node.js is managed through the event loop for I/O-bound tasks and worker threads for CPU-bound tasks, ...
