Understanding the nodejs event loop
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This document discusses the event loop in Node.js, which allows JavaScript to perform non-blocking I/O operations and asynchronous code. It explains that the event loop handles pending callbacks, timers, and incoming connections in different phases. Common asynchronous functions like setTimeout(), setImmediate(), and process.nextTick() are explained in terms of how they interact with the event loop. Finally, some common misconceptions about the event loop and asynchronous operations in Node.js are addressed.
Understanding the nodejs event loop
- 1. Understanding the Nodejs Event loop myths and magic Saurabh kumar, nuLL_Programmer saurav1431@gmail.com
- 2. What is Event loop??
- 4. What is Node.JS and does it Works?
- 5. Well, Node.js is a single threaded, non-blocking, asynchronous, event driven, JavaScript runtime built on V8 engine
- 6. index.js Output: Call Stack function foo(b){ var a = 3; return a* b + 5; } function bar(x){ var y = 2; return foo(x * y); } console.log(bar(4)); main();
- 7. index.js Output: Call Stack function foo(b){ var a = 3; return a* b + 5; } function bar(x){ var y = 2; return foo(x * y); } console.log(bar(4)); main();
- 8. index.js Output: Call Stack function foo(b){ var a = 3; return a* b + 5; } function bar(x){ var y = 2; return foo(x * y); } console.log(bar(4)); main(); console.log(bar(4));
- 9. index.js Output: Call Stack function foo(b){ var a = 3; return a* b + 5; } function bar(x){ var y = 2; return foo(x * y); } console.log(bar(4)); main(); console.log(bar(4)); bar(4)
- 10. index.js Output: Call Stack function foo(b){ var a = 3; return a* b + 5; } function bar(x){ var y = 2; return foo(x * y); } console.log(bar(4)); main(); console.log(bar(4)); bar(4) foo(8)
- 11. index.js Output: Call Stack function foo(b){ var a = 3; return a* b + 5; } function bar(x){ var y = 2; return foo(x * y); } console.log(bar(4)); main(); console.log(bar(4)); bar(4)
- 12. index.js Output: Call Stack function foo(b){ var a = 3; return a* b + 5; } function bar(x){ var y = 2; return foo(x * y); } console.log(bar(4)); main(); console.log(bar(4));
- 13. index.js Output: Call Stack function foo(b){ var a = 3; return a* b + 5; } function bar(x){ var y = 2; return foo(x * y); } console.log(bar(4)); main();
- 15. Example: console.log(“Hello”); setTimeout( function() { console.log(“geekle.us”); }, 3000); console.log(“Good Morning”); Stack
- 16. Example: console.log(“Hello”); setTimeout( function() { console.log(“geekle.us”); }, 3000); console.log(“Good Morning”); Stack main(); main(); console.log(“Hello”);
- 17. Example: console.log(“Hello”); setTimeout( function() { console.log(“geekle.us”); }, 3000); console.log(“Good Morning”); Stack main(); main(); console.log(“Good Morning”);
- 18. Example: console.log(“Hello”); setTimeout( function() { console.log(“geekle.us”); }, 3000); console.log(“Good Morning”); Stack main(); main();
- 19. Example: console.log(“Hello”); setTimeout( function() { console.log(“geekle.us”); }, 3000); console.log(“Good Morning”); Stack main(); main(); console.log(“geekle.us”);
- 20. Event loop is in picture
- 21. Event loop explained ┌───────────────────────────┐ ┌─>│ timers │ │ └─────────────┬─────────────┘ │ ┌─────────────┴─────────────┐ │ │ pending callbacks │ │ └─────────────┬─────────────┘ │ ┌─────────────┴─────────────┐ │ │ idle, prepare │ │ └─────────────┬─────────────┘ ┌───────────────┐ │ ┌─────────────┴─────────────┐ │ incoming: │ │ │ poll │<─────┤ connections, │ │ └─────────────┬─────────────┘ │ data, etc. │ │ ┌─────────────┴─────────────┐ └───────────────┘ │ │ check │ │ └─────────────┬─────────────┘ │ ┌─────────────┴─────────────┐ └──┤ close callbacks │ └───────────────────────────┘
- 22. SetImmediate() vs SetTimeout() setImmediate() is designed to execute a script once the current poll phase completes. SetTimeout() schedules a script to be run after a minimum threshold has elapsed
- 23. Process.NextTick() process.nextTick(() => { console.log(“execute in next iteration.”); }) console.log(“execute in current iteration.”); Output: execute in current iteration. execute in next iteration.
- 24. When to use Process.nextTick() 1. To allow users to handle errors. 2. Run a request before starting the next iteration of event loop, or the other event loop continues. 3. Clean unwanted resources. 4. Allow callback to run after call stack and before next iteration of event loop.
- 25. Misconception of NodeJS Event loop
- 26. Misconception 1: Everything that’s asynchronous like talking with database, working with filesystems is handled by a thread pool Reality: Libuv by default creates a thread poll with multiple thread to offload asynchronous work. Today’s operating system already provide asynchronous interfaces for many I/O tasks. Whenever possible libuv will use those interfaces avoiding usage of thread pool. But if there is no other option the thread pool will be used for asynchronous I/O/
- 27. Misconception 2: EventEmitter and Event loop are related. NodeJs event loop is the heart of Nodejs which provide non-blocking and asynchronous behaviour of an application, while eventemitter is extensively used when writing the NodeJs application.
- 28. That’s All