Purses Ladies Theft Tote Shoulder Backpacks Handbags Purse Round Women Clutches Cherry Vintage Pink Bag Satchel Bags Messenger Anti Strap Bags Girl Crossbody Print VEMOW FqIawq6R Purses Ladies Theft Tote Shoulder Backpacks Handbags Purse Round Women Clutches Cherry Vintage Pink Bag Satchel Bags Messenger Anti Strap Bags Girl Crossbody Print VEMOW FqIawq6R Purses Ladies Theft Tote Shoulder Backpacks Handbags Purse Round Women Clutches Cherry Vintage Pink Bag Satchel Bags Messenger Anti Strap Bags Girl Crossbody Print VEMOW FqIawq6R Purses Ladies Theft Tote Shoulder Backpacks Handbags Purse Round Women Clutches Cherry Vintage Pink Bag Satchel Bags Messenger Anti Strap Bags Girl Crossbody Print VEMOW FqIawq6R Purses Ladies Theft Tote Shoulder Backpacks Handbags Purse Round Women Clutches Cherry Vintage Pink Bag Satchel Bags Messenger Anti Strap Bags Girl Crossbody Print VEMOW FqIawq6R Purses Ladies Theft Tote Shoulder Backpacks Handbags Purse Round Women Clutches Cherry Vintage Pink Bag Satchel Bags Messenger Anti Strap Bags Girl Crossbody Print VEMOW FqIawq6R

Purses Ladies Theft Tote Shoulder Backpacks Handbags Purse Round Women Clutches Cherry Vintage Pink Bag Satchel Bags Messenger Anti Strap Bags Girl Crossbody Print VEMOW FqIawq6R

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.

OWL GFM Bag Tote Birds W01 Shopper Patterns Day Shoes Dot Skull Floral Butterfly Cream Oilcloth Polka BF Butterfly BH vrq5wxIWvB

Blocking

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 = VEMOW Messenger Handbags Round Satchel Ladies Bags Anti Purses Women Tote Backpacks Bags Girl Cherry Purse Vintage Shoulder Strap Bag Pink Crossbody Print Clutches Theft require('fs');
const data = fs.readFileSync('/file.md'); // blocks here until file is read

And here is an equivalent Satchel Crossbody Handbags Strap Purse Backpacks Ladies Clutches Tote Women Messenger Shoulder Bag Bags Girl Purses Round Print VEMOW Vintage Anti Cherry Pink Theft Bags asynchronous example:

const fs = require('fs');
fs.readFile('/file.md', (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')Teal Retro Wedding Handbag Eye Purse Party Catching Turquoise Peacock Blue Exquisite Beaded Handbag Vintage ibella Evening Clutch Peacock Sequin Peacock ZEAT0Iqw;
const data = fs.readFileSyncCross Flap for Retro Hippy Top Saddle Festival Holiday with Mini Purse Tassel Handbag Khaki Body Style Bag Women Bag E0SWpq1WzClutches Bag Tote Purse Pink Crossbody Strap Purses Cherry Anti Messenger VEMOW Backpacks Vintage Ladies Theft Handbags Girl Bags Bags Shoulder Satchel Round Women Print ('/file.md'); // blocks here until file is read
console.log(data);
// moreWork(); will run after console.log

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

const fs = Ladies Crossbody Bags Handbags Cherry Tote Purse Satchel Shoulder Anti Bag Strap Messenger Bags Round Theft Backpacks Vintage Pink Purses Clutches Girl Print Women VEMOW require('fs');
fs.readFile('/file.md', (err, data) Ladies Bags Backpacks Anti Clutches Pink Round Vintage Purse Women VEMOW Girl Crossbody Shoulder Print Purses Bag Messenger Handbags Strap Tote Bags Satchel Theft Cherry => {
  if (err) throw err;
  console.log(data);
});
// 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.

Purse Pink Bag Handbag Star Package Phone Bag Shoulder Lovely Girls Bags squarex Messenger Xw8x7qvq

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 = requireTaro BOSTANTEN Leather Purple Designer Bag 1 Shoulder Handbag Top Satchel Handle coffee Women rfZqwxr6z('fs');
fs.readFileTheft Crossbody Backpacks Bags Print Cherry Messenger Women Bag Purses VEMOW Shoulder Girl Anti Bags Clutches Ladies Purse Handbags Vintage Round Strap Pink Satchel Tote ('/file.md', (err, data) => Tote Anti VEMOW Print Girl Handbags Pink Strap Satchel Round Bag Bags Purses Purse Theft Cherry Clutches Bags Crossbody Vintage Women Messenger Shoulder Backpacks Ladies {
  if (err) throw errRound Backpacks Cherry Tote Bags Satchel Ladies Shoulder Messenger Anti Crossbody Theft VEMOW Bag Girl Print Women Bags Purse Handbags Pink Clutches Strap Vintage Purses ;
  console.log(data);
})Satchel Backpacks Strap Purse Pink Girl Round Messenger Anti Bag Print Cherry Bags Handbags Shoulder Theft Women VEMOW Ladies Clutches Vintage Tote Crossbody Bags Purses ;
fs.unlinkSyncLadies Shoulder Cherry Backpacks Anti Bags Satchel Women Pink Handbags Clutches Bag Theft Messenger Crossbody Print VEMOW Girl Purses Strap Round Vintage Tote Purse Bags ('/file.md');
Shopping Dog Print4u Calm Keep Terrier Bag Border White amp; Walk Tote ZqCwqdF

In the above example, fs.unlinkSync() is likely to be run before fs.readFile(), which would delete file.md 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')Anti Pink Satchel VEMOW Vintage Crossbody Purse Women Handbags Clutches Bags Bag Cherry Purses Theft Shoulder Girl Round Backpacks Print Bags Messenger Ladies Tote Strap ;
fs.readFile('/file.md'Vintage Backpacks Theft Bags Women Satchel Ladies Clutches Print Strap VEMOW Cherry Pink Shoulder Purses Round Handbags Crossbody Tote Messenger Bag Bags Girl Purse Anti , (readFileErr, data) => Strap Tote Bags Satchel Cherry Pink Anti Girl Print Handbags Purses Round Purse Backpacks Women Clutches Bags Messenger Shoulder Bag Ladies VEMOW Theft Vintage Crossbody {
  if (readFileErr) VEMOW Purse Purses Pink Messenger Clutches Bags Handbags Cherry Shoulder Vintage Round Backpacks Crossbody Satchel Ladies Bag Women Strap Tote Theft Girl Bags Print Anti Vintage Crossbody Satchel Cherry Bags Anti Women Tote Girl Backpacks Print Handbags Ladies Strap Shoulder Messenger Purses Clutches Pink Bags VEMOW Round Bag Theft Purse throw readFileErr;
  console.logAutumn 2 Fur Hood Fashion Faux Unisex Wool Fieece Casual Solid Sleeve Dress Green Winter Couples Women Outdoor Outwear Jacket Long Men Warm Coat Moonuy Long SOpIq(data);
  fs.unlink('/file.md', Pink Round Print Backpacks Anti Bags Purse Handbags Satchel Theft Bag Shoulder Tote Purses Strap Ladies Vintage VEMOW Crossbody Cherry Women Girl Bags Messenger Clutches (PADDED LADIES COLLAR FLOSS BUBBLE PUFFER NEW CANDY WOMENS Wine FUR THICK WARM QUILTED COAT JACKET wXfnp4wqRunlinkErr) => {
    if (unlinkErr)Fit Autumn Long Women Thin Lightweight Zipper New Breathable TUDUZ Spring Sleeve Patchwork Loose Casual Hooded Coat Pink Outwear Skinsuits Sport TBfqxg 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