Node event loop

Node Event Loop

Wants to see if his team member Pam should get a raise

Alan

Wants to schedule a 2 week vacation

Bob

● Check Pam’s sales figures● Compare to company performance● Give her the raiseAla

n

● Check available vacation hours● Schedule his vacation

Bob

IIS

Alan

Bob (Empty)

JimCome into my office

IIS

Alan

Bob (Empty)

JimI need Pam’s sales figures

IIS

Alan

Bob (Empty)

JimJim logs into sales tracker and looks up info

IIS

Alan

Bob (Empty)

Jimfew min latergives answer

IIS

Alan

Bob (Empty)

JimHow much vacation do I have left?

IIS

Alan

Bob (Empty)

JimJim logs out of sales tracker and into vacay tracker

IIS

Alan

Bob (Empty)

Jimfew min latergives answer

IIS

Alan

Bob (Empty)

JimFew more rounds of Jim logging in/out. Alan and Bob wait it out

Alan

Bob

An hour later they’re back at their desks

IIS

oh no, their work has piled up! :(

Threads take up resources

Threads cause context switching

Synchronous operations must wait to continue working

IIS

Node

Intern 1

Jim

Intern 2

Door slot

Node

Intern 1

Jim

Intern 2

Sales queryfrom Alan

Node

Intern 1

Jim

Intern 2

Node

Intern 1

Jim

Intern 2

Vacay queryfrom Bob

Node

Intern 1

Jim

Intern 2

Node

Intern 1

Jim

Intern 2

Answer

Node Jim calls Alan with the answer for his query

Meanwhile, Alan has been productive with his work

Single thread saves RAM and CPU

Queue for incoming I/O requests

Asynchronous ops, your code can keep working while you wait for a callback

Node