Adam Polak: Tworzenie oprogramowania to nie tylko implementacja nowych funkcjonalności, ale również utrzymanie istniejącego kodu oraz naprawianie potencjalnych błędów. Na prezentacji pokażę jak debugować zarówno uruchomioną wcześniej aplikację, jak i taką, nad którą dopiero pracujemy. Co to jest memory leak, po co nam debugger, co daje monitorowanie, czy dev tools to tylko frontend, a flame charts to coś więcej niż kolorowe wykresy – tego wszystkiego dowiecie się na prezentacji.

1. SHORT STORY ABOUT
NODE.JS DEBUGGING

2. SHORT STORY ABOUT NODE.JS DEBUGGING
AGENDA
▸ BASICS
▸ PROFILING
▸ MEMORY LEAK
▸ QUESTIONS

3. ADAM POLAK
HEAD OF NODE.JS
CREATOR OF KAKUNIN
ADAM.POLAK@THESOFTWAREHOUSE.PL
POLAK.ADAM1

4. LOOKING FOR AWESOME
NODE.JS DEVS

5. BASICS

6. CONSOLE.LOG()
ALL THE THINGS

7. THANK YOU

8. CONSOLE.LOG()
ALL THE THINGS

9. BASICS
const helloWorld = 'Hello World';
function hello() {
console.log(helloWorld);
}
hello();
CONSOLE.LOG / LOGGER

10. CONSOLE.LOG()
IS TRICKY

11. BASICS
CONSOLE.LOG
▸ NEITHER SYNC NOR ASYNC
▸ WRITES TO FILES ARE SYNC
▸ WRITES TO TERMINALS ARE ASYNC FOR
WINDOWS AND SYNC ON POSIX
▸ WRITES TO PIPES/SOCKETS ARE SYNC OF
WINDOWS AND ASYNC ON POSIX

12. CHROME DEV
TOOLS

13. BASICS
NODE INSPECT
node —inspect complicatedApp.js
node —inspect-brk complicatedApp.js

14. BASICS
INSPECT RUNNING PROCESS
kill -SIGUSR1 <process-id>
node> process._debugProcess(<process-id>)

15. BASICS
CHROME DEV TOOLS
▸ FULL DEBUGGER
▸ IDE INTEGRATION
▸ DECREASES PERFORMANCE
▸ CHECK OUT INSPECT-PROCESS LIB

16. PROFILING

17. HOW TO FIND
BOTTLENECKS?

18. FLAME GRAPHS

20. MEMORY
LEAKS

21. MEMORY LEAKS
MOST COMMON MEMORY LEAKS
▸ GLOBAL VARIABLES
▸ TIMERS / INTERVALS
▸ CLOSURES
▸ GROWING ARRAYS / OBJECTS

22. MEMORY LEAKS
const WebSocket = require('ws');
const clients = {};
let clientId = 0;
const wss = new WebSocket.Server({ port: 8080 });
wss.on('connection', function connection(ws) {
clients[++clientId] = {
connection: ws
};
ws.on('message', function incoming(message) {
console.log('received: %s', message);
});
ws.send('something');
});
EXAMPLE 1

23. MEMORY LEAKS
let handler;
function myFunction() {
const trololo = loremIpsum({
count: 200,
units: 'paragraphs'
});
const previousHandler = handler;
function innerFunction() {
if (previousHandler) return trololo;
}
return function(){};
}
setInterval(function() {
handler = myFunction();
}, 1000);
EXAMPLE 2

24. HOW TO FIND
MEMORY LEAK?

25. MEMORY LEAKS
const memwatch = require(‘memwatch-next');
const clients = [];
let clientId = 0;
const wss = new WebSocket.Server({ port: 8080 });
memwatch.on('leak', (stats) => {
console.log(‘Possible memory leak’);
});
OPTION 1 - MEMWATCH-NEXT

26. MEMORY LEAKS
OPTION 2 - HEAP DUMP

27. MEMORY LEAKS
const WebSocket = require('ws');
const clients = {};
let clientId = 0;
const wss = new WebSocket.Server({ port: 8080 });
wss.on('connection', function connection(ws) {
clients[++clientId] = {
connection: ws
};
ws.on('message', function incoming(message) {
console.log('received: %s', message);
});
ws.send('something');
});
LEAKY CODE

28. MEMORY LEAKS
BENCHMARKING TOOL
▸ WRK/WRK2
▸ JMETER
▸ SIEGE
▸ ARTILLERY

29. LETS FIND IT

30. QUESTIONS ?

31. THANK YOU