Why use node

Catalog

• Node What problems can be solved
  • What is a process
  • What is thread
  • What is multithreading
    • Advantages of multithreading
    • The disadvantages of multithreading
  • What is single thread
  • Synchronous and asynchronous
  • Synchronous asynchronous / Blocking non blocking
  • Node What is it?
  • Node Use scenarios

Node What problems can be solved

• Java It's a multithreaded language , There are some shortcomings in dealing with high concurrency ;Node It's single threaded , Can handle this problem well .
• When it comes to threads , Then let's talk about the concepts and differences between process and thread .

What is a process

When a program starts to run , It's a process , Processes include memory and system resources used by running programs and programs .

And a process is composed of multiple threads .

What is thread

A thread is an execution flow in a program , Each thread has its own special register ( Stack pointer 、 Program counter, etc ), But the code area is shared , That is, different threads can perform the same function .

What is multithreading

Multithreading refers to the program contains multiple execution flows , That is, you can run multiple different threads to perform different tasks in one program at the same time , That is to say, a single program is allowed to create multiple threads executing in parallel to complete their own tasks .

Advantages of multithreading

Can improve CPU Utilization ratio . In multithreaded programs , When a thread has to wait ,CPU You can run other threads instead of waiting , This greatly improves the efficiency of the program .

The disadvantages of multithreading

• Threads are also programs , So threads need to take up memory , More threads occupy more memory ;
• Multithreading needs coordination and management , So we need to CPU Time tracking thread ;
• Access to shared resources between threads will affect each other , We must solve the problem of competing for shared resources ;
• Too many threads lead to too complex control , In the end, it may cause a lot of problems Bug;

What is single thread

seeing the name of a thing one thinks of its function , There is only one thread in a program , Any operation is based on this thread , Then there is a blocking problem .

Synchronous and asynchronous

Synchronous and asynchronous focus on the message notification mechanism

• Synchronization is when a call is made , Before we get the results , The call does not return , Once called back , You get the return value . In short, the caller actively waits for the result of the call
• Asynchronous is the opposite , After the caller makes the call, the call returns directly , So no results returned . In other words, when an asynchronous procedure call is issued , Callers don't get immediate results , But after the call is made , The callee passes through the State 、 The notification or callback function handles the call .

Synchronous asynchronous / Blocking non blocking

The above is a boring concept in books , The following is an example in life to understand the relationship between synchronous asynchronous and blocking non blocking .

Now there's a scene , A boy confessed to a girl face to face . In the program, the boy corresponds to the client, that is, the caller , The girl corresponds to the caller on the server .

The following situations may happen after boys confess to girls ：

• The girl said that you wait for me to reply to you later . This waiting process for girls （ Callees ） It's synchronous , But for boys （ caller ） It is blocked .
• The girl said you should go back and do something else first , I'll think about it for two days and give you an answer . These two days for girls （ Callees ） It's asynchronous , For boys （ caller ） That is, non blocking , He can confess to other girls or do other things during this period , Let the girl know when she thinks about it .

The above mentioned synchronization blocking 、 Asynchronous non-blocking , Of course, there are two other situations （ Synchronous nonblocking 、 Asynchronous blocking ）, We won't discuss .

Node What is it?

stay Node I wrote one in libuv library , The idea of asynchronous non blocking is adopted , The bottom layer is actually implemented by multithreading .

Node Using event driven 、 Non-blocking type I/O Model of , Make it lightweight and efficient

Node One of the biggest reasons for this is the package manager npm, It is the largest open source library ecosystem in the world .

Node Use scenarios

• Now all companies are promoting Fore and aft end separation in , Use Node Make the middle layer .
  • Fore and aft end separation , Then there must be cross domain problems , Use Node Make a layer of interface encapsulation , This process will not cross domains ,Node Also in front-end control , For the front end, it will not span . That is to solve cross domain problems .
  • Of course, it can pass Nginx Solving cross domain problems . introduce Node It is also mainly to make the back-end responsibilities more focused on logical processing , Some data conversion can be handled by the front end , Make the responsibilities more clear .
• When applications need to deal with high concurrency scenarios , In multithreaded languages, such as Java It consumes a lot of memory , Is not recommended .
  • Chat server ： A lot of concurrent input and output
  • E-commerce website ： No complex logic , A lot of concurrent output （ A large number of users browse the website at the same time ）

Node Basics

todo

• nrm
• nvm

Node series - Next section Details of the event cycle