Download - Lessons learned from Node.js - Callbacks / Promises

Lessons Learned from Node.js

Jason YauDirector of EngineeringSamsung Accelerator

Tuesday, October 8, 13

1. Node.js

2. Methodology

3. Callbacks

4. Promises


Node.js is javascript on the server side.

It’s event-driven, non-blocking I/O model makes it FAST and

scalable. Tuesday, October 8, 13

In most languages, the code we write is

synchronous.

aka Blocking


Blocking


Waiting


In javascript, we do things differently; asynchronously.

aka Non-blocking


Non-Blocking


Parallel


Fast

http://benchmarksgame.alioth.debian.org/u64/benchmark.php?test=all&lang=v8&lang2=yarv&data=u64




Javascript


Popular


Methodology


I/O Latency• L1: 3 cycles

• L2: 14 cycles

• RAM: 250 cycles

• DISK: 41,000,000 cycles

• NETWORK: 240,000,000 cycles


A theoretical request.Request Process Results

Query DB or Web Service Write to log file

Format Response

= blocking / waitingTuesday, October 8, 13

Scale with Threads

Scale with Processes

Thread 1Thread 2Thread 3Thread 4

Process 1Process 2Process 3Process 4


Scale with Event LoopHandles many concurrent requests in a single

process / thread

Process 1

Thread Pool


Analogy


Event Queue Thread Pool

Event Loop

FilesystemNetworkProcessOther

Scale with Event Loop


Challenges with Callbacks


Recurring Question


Callbacks Example


Pyramid of Doom


Debugging


Parallel Example


Promises


What are promises?

A promise is an object that represents a one-time event, typically the outcome of an async task like an AJAX call. When a promise is returned, at first it is in a pending state.

Eventually it’s either:1. resolved - The promise is fulfilled with a value2. rejected - The promise is broken


Instead of calling a passed callback, return a promise.


Callback example


Return a promise


Passed callback


Return a promise


Parallel I/O


Promises are cleaner


Instead of calling a passed callback, return a promise.

Promise me you’ll remember promises.


Thank YouJason Yau

Director of Engineering, Samsung work: [email protected]
