Node family - understanding of blocking and non blocking

Endl 2021-05-03 14:43:25
node family understanding blocking non


original text :nodejs.org/en/docs/gui…

You should have some understanding of the concepts of blocking and non blocking :

Just to be brief , Most of the blocking is due to synchronous mode , Non blocking can be understood as asynchronous mode processing some time-consuming operations

Then again Node.js How to describe blocking and non blocking in ? The following is mainly about this problem :

Node What's blocking in ?

I/O Operation can be understood as the interaction with the system disk ( Data reading and writing ) Or network requests, etc

Blocking is everything else JS Code execution has to wait until the previous time-consuming I/O operation Or some network requests, etc . because Node There is an event loop to solve this problem , Let's say js In the process of re execution , The event loop has not been opened , In fact, it will cause congestion .

Actually in Node.js Under normal circumstances, there is also a blocking situation , as a result of Node Asynchronous processing for I/O The operation is friendly 【 Using the event loop 】, But for JavaScript There may be some CPU Intensive operation performance is relatively low . Some students may say , Why? CPU Intensive operation Node.js It can't be supported asynchronously ? Because you can understand these CPU Intensive operation , It's all synchronization code , Like a lot of for loop , Massive data computing, etc .

Node.js There are also some synchronization methods in the standard library of , Most of these methods are based on libuv To achieve the blocking effect .Node There are also some blocking methods in the native module of . But at the same time Node The corresponding asynchronous version of API.

What's up? libuv Well ? It's a multi platform, asynchronous I/O The library of operations . See the official website for details :libuv.org/

Node What's non blocking in ?

First of all, think about not limited to Node How to achieve non blocking in the context of ( asynchronous ) Well ?

To put it simply, two :

1) You can open multiple threads to handle concurrent operations

2) The pattern of the event cycle , If there are asynchronous operations in the event queue , After the end of the asynchronous operation , Call the corresponding callback function to process the asynchronous return result

Node.js It's single threaded , as a result of :Node.js The outer layer is made up of JavaScript Realized ,JavaScript The interpretation of execution is through V8`` engine To do the .

since JS The execution of is single threaded , Then we can't be JS During the process of interpretation and execution, open another thread to interpret and execute , therefore Node.js It's the second way to achieve non blocking ( Asynchronous operations ) Of .

Be careful not to mix Node Blocked and non-blocked API

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