![sync op vs. async op
const dinner = ['pasta', 'meat', 'tiramisù'];
dinner.forEach((food) => console.log(food));
const fs = require('fs');
dinner.forEach((food) => {
fs.readdir('.', () => {
console.log(food);
});
});
console.log('prosecco');
12
pasta
meat
tiramisù
prosecco
meat
tiramisù
pasta](https://image.slidesharecdn.com/node-161111090730/85/Node-js-concurrency-12-320.jpg)
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Node.js concurrency
- 1. Node.js concurrency Giacomo Fornari University of Padua, Sistemi concorrenti e distribuiti, 2016 - 2017
- 3. Two theses 1. waiting an I/O operation is a waste of time 2. thread-per-connection is memory-expensive “Non-blocking” L1-cache L2-cache RAM Disk Network The cost of I/O 3 cycles 14 cycles 250 cycles 41 000 000 cycles 240 000 000 cycles “Blocking” 3 Ryan Dahl: Introduction to Node.js, https://www.youtube.com/watch?v=M-sc73Y-zQA
- 4. Features ● Single-thread ● Highly concurrent ● No parallelism ● Event-driven Programmer’s point of view 4 “everything runs in parallel except your code” 1 1. http://blog.mixu.net/2011/02/01/understanding-the-node-js-event-loop/
- 5. Architecture Node Bindings Node Standard Library V8 Thread Pool Event Loop JavaScript C 5
- 6. Event Loop ● Has a sequential queue of functions linked with events ● Runs on single-thread ○ it has only one stack ● The functions are defined by callbacks ○ short execution time ○ they can yield events and asynchronous operations ● Implicit usage 6
- 7. Event Loop diagram Node.js Application Node.js Event Loop Thread 1 Thread 2 Thread n … (function, callback) Task 1 Task 2 Task 3 Return 1 Task 4 Callback 1 7
- 8. Thread Pool ● The strategy to achieve asynchronous I/O is not always a thread pool ○ Yes file-system operation ○ No network operations ● It has a fixed number of 4 thread ○ It is possible to set the number of thread before it is requested and created ● It has an internal queue of ○ function to execute ○ data for the function ○ function to call with the result 8
- 9. Thread delegation 9 Call function with callback Submit a work request Return to JS codeContinue processing Process the work request Finish processing and return result Call the callback Execute the callback of the function JavaScript C++ Main thread Worker thread
- 10. Event Loop and Thread Pool diagram 10https://strongloop.com/strongblog/node-js-is-faster-than-java/
- 11. return vs. callback function add(a, b) { return a + b; } function add(a, b, cb) { cb(a + b); } 11
- 12. sync op vs. async op const dinner = ['pasta', 'meat', 'tiramisù']; dinner.forEach((food) => console.log(food)); const fs = require('fs'); dinner.forEach((food) => { fs.readdir('.', () => { console.log(food); }); }); console.log('prosecco'); 12 pasta meat tiramisù prosecco meat tiramisù pasta
- 13. ● Concurrency reasoning easy ● No concurrent access of the state ● No locks ● No deadlock ● Still possible ○ starvation ○ race condition Conclusions 13
- 14. 14 References ● http://blog.mixu.net/2011/02/01/understanding-the-node-js-event-loop/ ● http://www.journaldev.com/7462/node-js-architecture-single-threaded-event-loop ● http://neilk.net/blog/2013/04/30/why-you-should-use-nodejs-for-CPU-bound-tasks/ ● https://oparu.uni-ulm.de/xmlui/bitstream/handle/123456789/2450/vts_8082_11772.pdf, ch. 5.5 ● https://strongloop.com/strongblog/node-js-is-faster-than-java/ ● http://www.slideshare.net/RonPerlmuter/nodejs-meetup-at-palo-alto-networks-tel-aviv ● http://www.slideshare.net/ganeshiyer7/nodejs-event-driven-concurrency-for-web-applications ● http://stackoverflow.com/questions/10680601/nodejs-event-loop ● http://stackoverflow.com/questions/22644328/when-is-the-thread-pool-used ● https://www.youtube.com/watch?v=M-sc73Y-zQA