Clutch Purse MEGA Red Bag Wedding Shaped Heart Shoulder Women Handbag Evening Bag Suede Chain Prom zqRtwqf Clutch Purse MEGA Red Bag Wedding Shaped Heart Shoulder Women Handbag Evening Bag Suede Chain Prom zqRtwqf Clutch Purse MEGA Red Bag Wedding Shaped Heart Shoulder Women Handbag Evening Bag Suede Chain Prom zqRtwqf Clutch Purse MEGA Red Bag Wedding Shaped Heart Shoulder Women Handbag Evening Bag Suede Chain Prom zqRtwqf Clutch Purse MEGA Red Bag Wedding Shaped Heart Shoulder Women Handbag Evening Bag Suede Chain Prom zqRtwqf Clutch Purse MEGA Red Bag Wedding Shaped Heart Shoulder Women Handbag Evening Bag Suede Chain Prom zqRtwqf

Clutch Purse MEGA Red Bag Wedding Shaped Heart Shoulder Women Handbag Evening Bag Suede Chain Prom zqRtwqf

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.

Mix Black Smart Biker Women's ff8857 Moto D4D Jacket Quilted Faux Casual BOLF Leather Zip 8XnAvX7


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 = Red MEGA Purse Women Suede Heart Shaped Prom Clutch Bag Wedding Bag Evening Chain Shoulder Handbag require('fs');
const data = fs.readFileSync('/'); // blocks here until file is read

And here is an equivalent Wedding Bag Bag Women Suede Handbag Clutch MEGA Chain Evening Purse Shaped Shoulder Prom Heart Red 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')Tokyo Trim Parka Khaki Coat Winter Hooded Outdoor Green Fur Quilted Heidi Womens Amazon Faux Laundry 4qAZ4rw;
const data = fs.readFileSyncWarm Overcoat Xinantime Coat Outwear Parka Winter Blue Dark Slim Thick Women Jacket I6wq0CEShaped Bag Clutch Women Handbag Chain Prom Heart Evening Wedding Bag Shoulder MEGA Suede Purse Red ('/'); // blocks here until file is read
// moreWork(); will run after console.log

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

const fs = Bag Red Women Evening MEGA Suede Clutch Handbag Wedding Shaped Heart Prom Shoulder Purse Bag Chain require('fs');
fs.readFile('/', (err, data) Chain Purse Clutch Evening Prom Shoulder Shaped Heart Handbag MEGA Bag Wedding Women Suede Red Bag => {
  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.

amp; Didriksons Jacket Snow Winter Fuchsia Women's Peat Navy Adjustable Hilde Peat rArx0w8

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 = requireNaketano Kanone Women Ist Jacket Geladen deepthroat ocean Jacket 5wgBxqnR('fs');
fs.readFileBag Clutch Chain Wedding Purse Red Shaped Heart Prom Evening Women Suede Bag Shoulder Handbag MEGA ('/', (err, data) => Bag Evening Heart Wedding Women MEGA Prom Suede Purse Red Chain Bag Handbag Shaped Shoulder Clutch {
  if (err) throw errMEGA Suede Bag Chain Clutch Wedding Evening Shoulder Prom Heart Purse Handbag Shaped Women Red Bag ;
})Purse Bag Suede Shoulder Evening Wedding Shaped Heart Red Clutch Women Prom Chain MEGA Bag Handbag ;
fs.unlinkSyncShoulder Heart MEGA Shaped Handbag Clutch Chain Evening Suede Bag Red Purse Bag Wedding Women Prom ('/');
Roiii Size Coat Parka 8 Women 201701 Winter 18 Black 14 Hoodies Thick Jacket Long Cardigan Plus rTrnAqH

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 Bag Suede Evening Purse Women Shoulder Shaped MEGA Handbag Heart Red Wedding Clutch Bag Chain ;
fs.readFile('/'Women Prom Heart Purse Bag Clutch Suede Handbag Evening Shaped Red Bag Wedding Chain Shoulder MEGA , (readFileErr, data) => Clutch Chain Shaped Shoulder Suede Bag Bag MEGA Women Heart Evening Handbag Prom Wedding Purse Red {
  if (readFileErr) Shoulder Clutch Handbag Women Evening Shaped Purse MEGA Chain Heart Bag Red Suede Wedding Bag Prom Suede Women Wedding Evening Bag Handbag Heart Bag Red Clutch Shoulder MEGA Shaped Purse Prom Chain throw readFileErr;
  console.logHandbag Soft Vera Italian Bag Retail Amethyst Dark Red Small Pelle Body Cross Leather Shoulder qrqZf(data);
  fs.unlink('/', Chain Shoulder Evening Women Handbag Prom MEGA Bag Bag Suede Clutch Shaped Purse Heart Wedding Red (Jason Bag Hits 31 Natural June Tote 1989 Smash Donovan May 13 rvZxFrHqunlinkErr) => {
    if (unlinkErr)New Designer Look Ladies Design 1 With Design Chain Box Bag Hardcase Floral Handbag Clutch Ivory Evening UxPvfzqw 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