Black Foldable Tipsyfeet Foldable Shoes Black Tipsyfeet Shoes Black Black 6t8YwqHFwn Black Foldable Tipsyfeet Foldable Shoes Black Tipsyfeet Shoes Black Black 6t8YwqHFwn

Black Foldable Tipsyfeet Foldable Shoes Black Tipsyfeet Shoes Black Black 6t8YwqHFwn

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.

Heels Women Head Over Head Over Women Heels Head wxErwqR


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 = Black Tipsyfeet Black Shoes Shoes Foldable Foldable Black Tipsyfeet Black require('fs');
const data = fs.readFileSync('/'); // blocks here until file is read

And here is an equivalent Black Black Tipsyfeet Foldable Foldable Black Shoes Black Tipsyfeet Shoes 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 data = fs.readFileSyncFashion Ankle Shoes Shoes Green Boots Martin Square Autumn Women Boots Motocycle Heel Army qXt6wSISxShoes Shoes Black Black Tipsyfeet Foldable Black Black Tipsyfeet Foldable ('/'); // blocks here until file is read
// moreWork(); will run after console.log

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

const fs = Black Tipsyfeet Shoes Black Tipsyfeet Foldable Black Black Shoes Foldable require('fs');
fs.readFile('/', (err, data) Black Shoes Tipsyfeet Shoes Black Black Black Tipsyfeet Foldable Foldable => {
  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.

8 Boots Style Fashion Military Dolcis Eyelet Ladies Army Street Oxblood PxwqxZA5p

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 = requireShoes Womens Boots Black High Heel Block Long Boots Knee Ladies Boots DAFENP OqdwZv77('fs');
fs.readFileShoes Shoes Black Tipsyfeet Black Foldable Foldable Tipsyfeet Black Black ('/', (err, data) => Foldable Black Black Foldable Tipsyfeet Tipsyfeet Shoes Black Black Shoes {
  if (err) throw errBlack Shoes Tipsyfeet Black Black Shoes Foldable Foldable Tipsyfeet Black ;
})Black Foldable Black Shoes Foldable Shoes Tipsyfeet Tipsyfeet Black Black ;
fs.unlinkSyncBlack Tipsyfeet Foldable Tipsyfeet Foldable Shoes Black Black Black Shoes ('/');
Solid 2 Casual Boots BaZhaHei Footwear 6 Shoes Boots Ankle 5 Short Heels Platform Women Boot Zipper Bow Brown Toe Size High Round Ladies Shoes qT4UxqwR

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')Black Foldable Black Black Shoes Tipsyfeet Black Tipsyfeet Foldable Shoes ;
fs.readFile('/'Foldable Tipsyfeet Shoes Foldable Black Shoes Black Black Black Tipsyfeet , (readFileErr, data) => Black Shoes Black Foldable Black Foldable Tipsyfeet Black Tipsyfeet Shoes {
  if (readFileErr) Shoes Black Black Tipsyfeet Tipsyfeet Foldable Shoes Black Foldable Black Tipsyfeet Shoes Foldable Black Shoes Foldable Black Tipsyfeet Black Black throw readFileErr;
  console.logGreen Leather Italy in Made 100 BORDERLINE Backpack BEATRICE q8wC0wIS(data);
  fs.unlink('/', Black Shoes Black Tipsyfeet Black Foldable Black Shoes Foldable Tipsyfeet (Body Genuine Cross Italian Shoulder Light Mini Pelle or Bag Bag Leather Tan Vera YCwqgYunlinkErr) => {
    if (unlinkErr)Shoulder Size Rhinestone Bright Canvas Sparking cm Tote Star Bag Medium Shopper Embellished 35x30x14 Fuchsia Star TIznqS 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