JavaScript execution in Node.js is single threaded, so concurrency refers to the event loop's capacity to execute JavaScript callback functions after completing other work. Any code that is expected to run in a concurrent manner must allow the event loop to continue running as non-JavaScript operations, like I/O.

Sergio Bernal

Node.js foundations

Programming

Node.js

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What is Node.js?

Sergio Bernal

Why does Node.js exists?

Sergio Bernal

Blocking is when the execution of additional JavaScript in the Node.js process must wait until a non-JavaScript operation completes. This happens because the event loop is unable to continue running JavaScript while a blocking operation is occurring.

Sergio Bernal

Blocking methods execute synchronously and non-blocking methods execute asynchronously.

Sergio Bernal

In Node there is no such start-the-event-loop call. Node simply enters the event loop after executing the input script. Node exits the event loop when there are no more callbacks to perform. This behavior is like browser JavaScript

Sergio Bernal

The event loop is what allows Node.js to perform non-blocking I/O operations — despite the fact that JavaScript is single-threaded — by offloading operations to the system kernel whenever possible.

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Since most modern kernels are multi-threaded, they can handle multiple operations executing in the background. When one of these operations completes, the kernel tells Node.js so that the appropriate callback may be added to the poll queue to eventually be executed.

Sergio Bernal

When Node.js starts, it initializes the event loop, processes the provided input script (or drops into the REPL) which may make async API calls, schedule timers, or call process.nextTick(), then begins processing the event loop.

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These are the phases of the event loop. Each phase has his own queue. timers pending callbacks idle, prepare poll <- incoming: connections, data etc. check close callbacks

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Each phase has a FIFO queue of callbacks to execute.

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While each phase is special in its own way, generally, when the event loop enters a given phase, it will perform any operations specific to that phase, then execute callbacks in that phase's queue until the queue has been exhausted or the maximum number of callbacks has executed

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12:33 > This diagram looks basically identical for node, instead of web APIs we have C++ APIs and the threading is being hidden from you by C++

Sergio Bernal

Just because Node is designed without threads, doesn't mean you cannot take advantage of multiple cores in your environment. Child processes can be spawned by using our child_process.fork() API

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V8 The V8 library provides Node.js with a JavaScript engine, which Node.js controls via the V8 C++ API. V8 is maintained by Google, for use in Chrome.

Sergio Bernal

V8 is Google’s open source high-performance JavaScript and WebAssembly engine, written in C++. It is used in Google Chrome, the open source browser from Google, and in Node.js, among others.

Sergio Bernal

V8 implements ECMAScript and WebAssembly. Can run standalone, or can be embedded into any C++ application

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Libuv, a C library that is used to abstract non-blocking I/O operations to a consistent interface across all supported platforms. It provides mechanisms to handle file system, DNS, network, child processes, pipes, signal handling, polling and streaming.

Sergio Bernal

It's very hard to uphold individual liberty when the person you're representing is often a crook.

Jed S. Rakoff

I am not a spiritual guy, but all of a sudden I felt the need to really feel things.

Scott Baio

Good night Good night Far flies the light But still Gods love Shall shine above Making all bright Good night Good night

Victor Hugo

Theres more to us than the moment we made a bad decision.

Jenji Kohan

Record-breaking is not getting boring. I am definitely happy with that.

Katarina Johnson-Thompson

The real amazing thing about all of this is I think I've maintained the mentality of a musician throughout it all, which I'm proudest of. And I'm still playing on people's records and singing on people's records.

Vince Gill

Marxism does not make sense, and I am the first one to say this.

Todor Zhivkov

I'm persuaded today that the only way you can get into another country with a different culture from your own is to find a local partner who knows the market. Discovering this felt like small children discovering that if you put a bobby pin into an electric plug you get a shock!

Roberto Civita

I don't want to be involved in endless media gossip.

Kate Adie

Until 1956, America treated Israel not much differently from other friendly states.

George Ball

Stop being afraid of what could go wrong and think of what could go right.

Unknown

I've been very fortunate in the things I've had in my life. But, at the same time, I wish I had the same types of memories as everyone else.

Alfonso Ribeiro

Do your job and demand your compensation - but in that order.

Cary Grant

The essence of a democracy is a free electorate.

Arlen Specter

I knew what I wanted to do from the time I was 5.

Lenny Kravitz

I like being a mother. For some people, it's so much work that it can be a burden. But it's not for me, maybe because I had my daughter, Valentina, later on in life, at 41.

Salma Hayek

My first memory - at about four - was of numbers. The doctors who study me think a combination of mild autism and seizures I had when I was three have made me experience numbers the way I do.

Daniel Tammet

A Fiat Panda, it's the best car in the world.

Luca Cordero di Montezemolo

I see if I can make human beings look like reptiles.

Ralph Steadman

I love Andre 3000 from OutKast. I think we'd complement each other, but I'm hoping he's got a good sense of humour.

Paloma Faith

What influences our behavior, and what our level of responsibility is, are very complex issues. And anytime we try to make this simplistic, we don't serve people well.

John Ortberg

You know what I did? I turned down an offer to do 'Enemy of the People' with Steve McQueen. It doesn't matter that the film was never really released. A movie like that, successful or not, adds to your credits. It leads to other roles.

Diane Ladd

Hope is a belief in a better tomorrow.

Lailah Gifty Akita

Cooking is in an honest profession where you cannot hide and let others do the work for you. You have to show up, work hard and prove you can do it faster and better. And find a mentor who will recognize your talent and push you in the right direction.

Marcus Samuelsson