CODEWITHSUNDEEP
javascriptnode.jsasynchronousv8libuv
RT Bathula
RT Bathula

Reputation: 189

What happend in libuv when you make parallel requests

As Javascript is a single threaded, how libuv handles when i manage to make two requests parallely? Eg: Making array of promises and resolving latter

Upvotes: 0

Views: 633

Answers (2)

jfriend00
jfriend00

Reputation: 707238

I presume what you're really asking is how does libv8 handle two asynchronous requests that are "in flight" at the same time. Since Javascript is single thread, you can't start them at the same moment. One will be started, then your JS will be able to run some more and start the second one. They will both be "in process" at the same time.

First off, the library used in nodejs is generally called libuv, not libv8. Here's the doc for libuv.

The answer for how libuv does this is that it depends upon the type of asynchronous operation. Here's a diagram from the libuv site:

enter image description here

Disk I/O in libuv uses native threads via a thread pool. A native thread runs each disk I/O operation and then it completes, it then puts an event into the nodejs event queue so that when nodejs is available, it can pull that event from the event queue and call the callback registered for the async I/O operation. This functionality originally came from libeio, but is apparently its own implementation now.

Networking operations in libuv use native OS async capabilities such as epoll, kqueue and IOCP.

Upvotes: 3

Johnathan Ralls
Johnathan Ralls

Reputation: 141

technically you don't make the request parallel, one does come first. that one starts first, but it listens or checks for one if it is finished, and then the other, and back and forth until one finishes first.

Upvotes: 1

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