Tadpole Biography: Principles and implementation of module hot deployment on nodeJS

Twelve o ‘clock at night, in bed

Rich woman: Here’s 500 yuan for you. Thank you

Tadpole: No hard work, master

Rich woman: My husband is coming home. You can go now

Tadpole: Yes, master

Then the tadpole jumped down from the third floor villa

Tadpole is a programmer, but also a technician

Code by day, foot by night

Because of years of knocking code, so superb fingering

Always push the customer to the sun dragon

The rich woman is young and rich, but short of love

For being married to an 80-year-old husband

Little tadpole obedient live not sticky people

Won the heart of a rich woman

See you again

Rich woman: so boring, please me quickly

Tadpole: Master, LET me use my finger to type “Dijkstra shortest Path algorithm” on your leg

Rich woman: You’ve done that before

Tadpole: I’ll write javascript Advanced Programming on your back with my chest hair.

Rich woman: No

Tadpole: Then I will show you a ventriloquism with my tongue

Rich woman: Tongue? A room?

Tadpole: Don’t think too much about it. It’s a regular performance

Then the little tadpole performed a piece of tongue broken rock

The rich woman rejoiced, and the applause was prolonged

After the performance, the rich woman blushed

Rich woman: I like you

Tadpole: I like myself, too

Woman: Do you love me

Tadpole: I can’t fall for clients

Rich woman: How can I get your heart

Tadpole: kill me, pull out your heart, hee hee

Rich woman: Hee hee

Rich woman: By the way, come to my girls’ party next week

Tadpole: Won’t you take your husband

Rich woman: He’s 80 years old. He’s a disgrace

Tadpole: That will cost me more

Rich woman: How much

Tadpole: 200 yuan for two hours

Women: deal

Girlfriends party

8:00 p.m., fancy hotels, ostentatious displays of wealth

Bestie A: I bought A bag, only 100,000 yuan, so cheap

Bestie B: I packed three little milk dogs and let them fight the landlord all night

Bestie C: My husband has many small animals, such as BMWS, Land Rovers and Jaguars

Rich woman silently forward: I bought a siheyuan in Beijing

The other girls stopped talking

“The tadpole realized

This was no ordinary meal

But a feast to pack to force between girlfriends

Tadpole: What do you need me to do

Rich woman: I need you to beat their boy pet

After drinking three cruise

It’s time to show off your boy’s pet

Each girl brought her own boy pet

There are muscle men, high-class ducks, male models and so on

Muscle guy goes on stage with an eight-pack and a crotch the size of a punching bag

Male models go straight for long legs and ugly faces

The senior duck sticks out his tongue on the stage and says, “Slightly slightly…” The sound of

Boys and girls have different strengths

She won applause from her girlfriends

It’s the tadpole’s turn

A plaid shirt in shit-green

stupefied

The host ask: hot chicken, you want to show what specialty

Tadpole: Tongue broken rock

Host: Other than that

Tadpole: Chest hair broken rock

Host rage: I suspect you are to smash the field

Tadpole: Yeah, I’m just here to crash

The host called in 20 security guards

Ten seconds later the guards all fell to the ground convulsing

Tadpole chest hair covered in cryptic javascript code

Host: I’m sorry, Dad, I offended you just now

Host: Dad, please introduce yourself to the audience

Tadpole from the bag out of ten million dollars (rich woman sent)

Lit and thrown out of the 98th floor

Burning money flew in the air

The tadpole said, “I am a man of different colors who cheaters and plays with women’s feelings.”

All the women in the audience were screaming

He bled from his seven orifice because of excessive excitement

Boys and girls see their masters licking tadpoles like crazy

I feel green

Compere: dad you still have what gentle point of special skill show to everybody

Tadpole: I want to sing a song of Sun Yanzhi’s “green light” for all the male hot chicken present here

“

“Green light”

Love is like a green light

All over your head

I blame my sister-in-law for being too pretty

Don’t blame dad for being heartless

It’s your spicy chicken

Ah, green light, ah, green light

To illuminate you and me

“

Boys: Tadpole, you’ve gone too far

Tadpole: each according to his ability to be scum

Boys: What are you trying to do

Tadpole: I want to dance on your grave

Male pets explode and scratch their heads like crazy

He jumped off the 98th floor

The tadpole won the race

Became the number one boy pet

Hotel balcony, breeze blowing

Rich woman: Thank you for tonight

Tadpole: For the money, I should

Rich woman: I like you

Tadpole: I like myself, too

Woman: Do you love me

Tadpole: I can’t fall for clients

Rich woman: How can I get your heart

Tadpole: kill me, pull out your heart, hee hee

Rich woman: Hee hee

The gang bosses

Inside, pinch your feet

Rich woman: I’m dying

Tadpole: What’s wrong

Rich woman: My husband has a woman outside

Rich woman: he’s a gangster, trying to kill me, with my mistress

Tadpole gently caresses rich woman’s face: fool, before this, I will kill him

Little tadpole and rich woman embrace kiss together

Pull a thread between your mouths

The tadpole disappears into the night sky

The assassination of bosses

Twelve o ‘clock at night

Outside the hotel room of a mob boss

A small card was tucked in

It says “Miss Bao”

And a picture of a tadpole in a speedo

Mob bosses have weird quirks

Like a little milk dog with a hairy chest

The tadpole fulfilled all his fantasies about being a Suckling dog

Sure enough, the door opened

The tadpole stuck a thousand chest hairs into the big guy

Big Guy: You… Who are you

Tadpole: I’m your father

Big guy: Why did you kill me

Tadpole: Because I’m your father

Big man: Can we not mention dad

Tadpole: I had an affair with your wife

Gang leader, Cu, died at 80

For the assassination of a mob boss

On the way back that night

Little tadpole being hunted by 1,000 killers

I used up my last chest hair

The tadpole is outnumbered

She was dying in a pool of blood

As he was dying, the rich woman emerged from the killers

She smiled and stabbed the tadpole with a knife

I tore my heart out

The tadpole looked at her in horror

Rich woman: I finally got your heart, hee hee

(after)

Author: The tadpole in the first place

Wechat official account: Front-end Diaosi

Making: github.com/airuikun/bl…

Principle and Implementation of Hot Deployment of Modules on NodeJS

background

As you all know, if there is any code change in the back-end service started by NodeJS, the process must be restarted for the code to take effect.

When the NodeJS process is restarted, fathers will access the service, and there will be 502 bad Gateway for a short time. Fathers will not be happy

If you have a watch mechanism on your server

When the code on the server changes frequently, or frequently in a short period of time, it stays 502 bad Gateway

The so-called “restart for a while, keep restarting straight.”

Recently, when making relevant requirements for cloud compilation, frequent changes of service codes and frequent updates of code function modules occurred in a short period of time, and the updated codes took effect when the service could not be restarted.

This involves the concept of hot deployment, where newly deployed code takes effect without restarting the service.

Let me explain the principles and implementation of hot deployment to dads

Why code doesn’t work in real time

When loading a function module via require(‘xx/xx.js’), Node will cache the result of require(‘xx/xx.js’) in require.cache(‘xx/xx.js’)

When we call require(‘xx/xx.js’) multiple times, node does not reload and instead reads directly from the require.cache(‘xx/xx.js’)

So when dad changes the xx/xx.js file on the server, Node only reads the cache and does not load dad’s latest code

Source code address and use

In order to implement this hot deployment mechanism, it is necessary to look up information on the Internet and dig holes everywhere

The following code is refined, fully operational, hot deployment fundamentals that you can extend on your own: Smart-Node-reload

Note The latest version of Node 12 May cause an error. The require.cache has been modified and the problem has been reported to the authorities

Git Clone will run directly without installation

    npm start
Copy the code

This is when hot deployment change listening is turned on

How do you see the effect

Dad, look at the /hots/hot.js file

    const hot = 1
    module.exports = hot
Copy the code

Change the first line of code to const hot = 111

    const hot = 111
    module.exports = hot
Copy the code

You can see that the terminal is listening for code changes, and then dynamically loading your latest code and getting the result of execution:

Hot deployment file: hot.js, result: {'hot.js': 111 }
Copy the code

The hot deployment service listens for the code changes, reloads the code, and the dads can get the latest code execution results in real time, all while running online without the Node process restarting

The source code parsing

LoadHandlers main function

const handlerMap = {};/ / cache
const hotsPath = path.join(__dirname, "hots");

// Load the file code and listen for changes in the contents of the specified folder
const loadHandlers = async() = > {// Iterate over all files in the specified folder
  const files = await new Promise((resolve, reject) = > {
    fs.readdir(hotsPath, (err, files) => {
      if (err) {
        reject(err);
      } else{ resolve(files); }}); });// Initialize all files and cache the results of each file in the handlerMap variable
  for (let f in files) {
    handlerMap[files[f]] = await loadHandler(path.join(hotsPath, files[f]));
  }

  // Listen for changes in file contents in the specified folder
  await watchHandlers();
};
Copy the code

LoadHandlers are the main function of the whole hot deployment service. We specify that the hoTS folder in the server root is used to listen for changes and hot deployment

Use fs.readdir to scan all files in the HOTS folder, loadHandler method to load and run each scanned file, and cache the result in handlerMap

File change listening is then turned on using the watchHandlers method

WatchHandlers listen for file changes

// Monitor file changes under the specified folder
const watchHandlers = async() = > {// It is recommended to use chokidar's NPM package instead of folder listening
  fs.watch(hotsPath, { recursive: true }, async (eventType, filename) => {
    // Get the absolute path to each file
    // Require. Resolve. After the path has been concatenated, it will take the initiative to determine whether the file in this path exists
    const targetFile = require.resolve(path.join(hotsPath, filename));
    // When you load a module in require, the module's data will be cached in require.cache. The next time you load the same module, it will go directly to require.cache
    // The first thing we do in a hot load deployment is clear the require.cache of the corresponding file
    const cacheModule = require.cache[targetFile];
    // Remove parent's references to the current module in require.cache, otherwise it will cause memory leaks
	/ / the record once triggered by a single line of code "attack", "https://cnodejs.org/topic/5aaba2dc19b2e3db18959e63
	/ / the line of the delete the require. Cache memory leak caused by murder, https://zhuanlan.zhihu.com/p/34702356
    if (cacheModule.parent) {    
        cacheModule.parent.children.splice(cacheModule.parent.children.indexOf(cacheModule), 1);
    }
    // Clear the require.cache cache of the module corresponding to the specified path
    require.cache[targetFile] = null;

    // Reload the changed module file to achieve hot loading deployment effect and update the reloaded result to the handlerMap variable
    const code = await loadHandler(targetFile)
    handlerMap[filename] = code;
    console.log("Hot deployment file:", filename, ", execution result:, handlerMap);
  });
};
Copy the code

The watchHandlers function listens for changes to files in the specified folder, cleans and updates the cache.

Use fs.watch native function to listen for file changes under hoTS folder. When the file changes, calculate the absolute path targetFile of the file

Cache [targetFile] = null; require. Cache [targetFile] = null;

Cache [targetFile].parent is a reference to the parent level of the cache

    if (cacheModule.parent) {    
        cacheModule.parent.children.splice(cacheModule.parent.children.indexOf(cacheModule), 1);
    }
Copy the code

LoadHandler Loads the file

// Load the code for the specified file
const loadHandler = filename= > {
  return new Promise((resolve, reject) = > {
    fs.readFile(filename, (err, data) => {
      if (err) {
        resolve(null);
      } else {
        try {
          // Use the Script method of the VM module to precompile the changed file code, check for syntax errors, and find out whether there are syntax errors and other errors in advance
          new vm.Script(data);
        } catch (e) {
          // Syntax error, failed to compile
          reject(e);
          return;
        }
        // After the compile passes, re-require to load the latest code
        resolve(require(filename)); }}); }); };Copy the code

The loadHandler function loads the specified file and verifies the syntax of the new file.

Read the contents of the file with fs.readfile

Use the node native VM module vm.Script method to precompile the changed file code, check syntax errors, and find out whether there are syntax errors and other errors in advance

If the check passes, use the resolve(require(filename)) method to load the file require again and automatically add the file to require.cache

The end:

That’s all for hot deployment, smart-Node-reload

This code is my minimalist code, easy for everyone to read and understand, interested partners can use this code to further expand

Well… After writing this article, it is already two o ‘clock in the morning. It is not easy to write this article. Please star, follow, like and follow me