The Node.js Event Loop, Timers, and process.nextTick()

Phases Overview

• timers: this phase executes callbacks scheduled by setTimeout() and setInterval().
• pending callbacks: executes I/O callbacks deferred to the next loop iteration.
• idle, prepare: only used internally.
• poll: retrieve new I/O events; execute I/O related callbacks (almost all with the exception of close callbacks, the ones scheduled by timers, and setImmediate()); node will block here when appropriate.
• check: setImmediate() callbacks are invoked here.
• close callbacks: some close callbacks, e.g. socket.on('close', ...).

Links

• https://nodejs.org/en/docs/guides/event-loop-timers-and-nexttick/
• https://nodejs.org/api/cli.html#cli_uv_threadpool_size_size
• https://www.youtube.com/watch?v=zphcsoSJMvM
• https://www.youtube.com/watch?v=P9csgxBgaZ8
• https://nodejs.org/uk/docs/guides/dont-block-the-event-loop/
• https://medium.com/the-node-js-collection/what-you-should-know-to-really-understand-the-node-js-event-loop-and-its-metrics-c4907b19da4c