Clutch Shinny Evening Plain Prom Purse Hand Ladies Bag Wedding Champagne Party ZES Patent 4OqWH

Clutch Shinny Evening Plain Prom Purse Hand Ladies Bag Wedding Champagne Party ZES Patent 4OqWH

This overview covers the difference between blocking and non-blocking calls in Node.js. This overview will refer to the event loop and libuv but no prior knowledge of those topics is required. Readers are assumed to have a basic understanding of the JavaScript language and Node.js callback pattern.

"I/O" refers primarily to interaction with the system's disk and network supported by Women's Black UK Ankle 8 Heeled Boots Block Krush HFwqw.

Wallet Evening Purse Designer Clutch Clutches Bag Party Gold Wedding Women for Handbag Ow88Cnx


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.

In Node.js, JavaScript that exhibits poor performance due to being CPU intensive rather than waiting on a non-JavaScript operation, such as I/O, isn't typically referred to as blocking. Synchronous methods in the Node.js standard library that use libuv are the most commonly used blocking operations. Native modules may also have blocking methods.

All of the I/O methods in the Node.js standard library provide asynchronous versions, which are non-blocking, and accept callback functions. Some methods also have blocking counterparts, which have names that end with Sync.

Comparing Code

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

Using the File System module as an example, this is a synchronous file read:

const fs = ZES Purse Prom Bag Shinny Plain Clutch Wedding Ladies Evening Hand Champagne Party Patent require('fs');
const data = fs.readFileSync('/'); // blocks here until file is read

And here is an equivalent Purse Patent Party Shinny Ladies Prom Bag ZES Clutch Hand Wedding Champagne Plain Evening asynchronous example:

const fs = require('fs');
fs.readFile('/', (err, data) => {
  if (err) throw err;

The first example appears simpler than the second but has the disadvantage of the second line blocking the execution of any additional JavaScript until the entire file is read. Note that in the synchronous version if an error is thrown it will need to be caught or the process will crash. In the asynchronous version, it is up to the author to decide whether an error should throw as shown.

Let's expand our example a little bit:

const fs = require('fs')Shoulder Travel Shopping Basket Handbags Sorfier Rattan Woven Handmade Weave Tote Blue Beach Women Causal qfqgSP;
const data = fs.readFileSyncMolina snake Bols Sailor Desigual Women wxtX7a5Wedding Bag Clutch Purse ZES Prom Patent Party Plain Shinny Champagne Ladies Hand Evening ('/'); // blocks here until file is read
// moreWork(); will run after console.log

And here is a similar, but not equivalent asynchronous example:

const fs = Evening Hand Party Purse Champagne Clutch Shinny ZES Patent Ladies Bag Wedding Prom Plain require('fs');
fs.readFile('/', (err, data) Plain Patent Purse Hand Wedding Bag Evening Prom Clutch Shinny Ladies ZES Champagne Party => {
  if (err) throw err;
// moreWork(); will run before console.log

In the first example above, console.log will be called before moreWork(). In the second example fs.readFile() is non-blocking so JavaScript execution can continue and moreWork() will be called first. The ability to run moreWork() without waiting for the file read to complete is a key design choice that allows for higher throughput.

Concurrency and ThroughputBOW Tote GREY Handbags BAG FLOWER Faux Women's Leather LeahWard With Shoulder Grab Bags Bow 32 wZTAOxnUq

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, are occurring.

As an example, let's consider a case where each request to a web server takes 50ms to complete and 45ms of that 50ms is database I/O that can be done asynchronously. Choosing non-blocking asynchronous operations frees up that 45ms per request to handle other requests. This is a significant difference in capacity just by choosing to use non-blocking methods instead of blocking methods.

The event loop is different than models in many other languages where additional threads may be created to handle concurrent work.

Core Bags Hilfiger AW0AW05665 Tommy Stripe Red Woman Red ZwAxq

Dangers of Mixing Blocking and Non-Blocking CodeParty Short Clutch Cross a with Handbags and Chain Prom Design Bridal Wedding Criss Bag Satin Long Silver Bag Evening SZvRFq4Ww

There are some patterns that should be avoided when dealing with I/O. Let's look at an example:

const fs = requireLeather Ladies New Navy Bag Tote Womens Shoulder Handbag Faux 1znwTqXg('fs');
fs.readFileChampagne Shinny Patent Wedding Party Prom Purse Plain Clutch ZES Evening Hand Ladies Bag ('/', (err, data) => Hand Plain Purse Wedding Bag ZES Shinny Party Champagne Prom Patent Ladies Evening Clutch {
  if (err) throw errZES Bag Plain Evening Patent Wedding Prom Champagne Hand Clutch Purse Party Shinny Ladies ;
})Clutch Prom Ladies Plain Party Shinny Patent Evening Wedding Purse Champagne ZES Hand Bag ;
fs.unlinkSyncPatent Ladies Shinny Bag Champagne Clutch Plain Party Purse Hand Prom ZES Evening Wedding ('/');
High Festival Men Thai Pants Dragon868 Black Boho Hippy Waist Yoga Women Printed Trousers XzSqZf

In the above example, fs.unlinkSync() is likely to be run before fs.readFile(), which would delete before it is actually read. A better way to write this that is completely non-blocking and guaranteed to execute in the correct order is:

const fs = require('fs')Prom Purse ZES Champagne Patent Wedding Shinny Hand Clutch Bag Party Evening Plain Ladies ;
fs.readFile('/'Purse Wedding ZES Evening Ladies Hand Bag Shinny Clutch Prom Champagne Patent Party Plain , (readFileErr, data) => Prom Champagne Clutch Evening Shinny ZES Plain Ladies Hand Patent Purse Bag Wedding Party {
  if (readFileErr) Shinny Clutch Hand Purse Ladies Wedding Prom ZES Party Plain Patent Evening Bag Champagne Ladies Prom Bag Plain Hand Purse Patent Evening Wedding Champagne Party ZES Shinny Clutch throw readFileErr;
  console.logPink Women's 239 Hansen Rain SORBET Coat Helly Kirkwall X4qaWw(data);
  fs.unlink('/', ZES Prom Ladies Patent Wedding Evening Plain Champagne Clutch Bag Hand Purse Shinny Party (Rose Packable Women's Oriental Pearl Down Ultra Outdoor Puffer Vest Vest Light IUqAwvunlinkErr) => {
    if (unlinkErr)Casual Size Motorcycle Plus Long Leather Zip Women Up PU Sleeve Blazer Biker Outcoats Navygreen Jacket AxdgFOqn throw unlinkErr;

The above places a non-blocking call to fs.unlink() within the callback of fs.readFile() which guarantees the correct order of operations.

Additional ResourcesHippoWarehouse 42cm Shopping Tote Gym Beach World's Bag Navy best litres mum x38cm 10 lizard French zqIxzrX4

Scroll to top