[Use AI to systematize knowledge] Unlock a new world of asynchronous programming!

Article directory

I. Preface
- Introduction
- Application of Asynchrony in Computer Programming
II. Synchronous and asynchronous
- Definition and Difference
- Disadvantages of synchronous programming
III. Asynchronous programming
- definition
- Application Scenario
- Callback
- Promise object
- async/await keyword
- event loop
IV. Asynchronous programming example
- Using asynchronous programming in Node.js
- Asynchronous HTTP request implementation
- Asynchronous file operations
V. Advantages of Asynchronous Programming
VI. Challenges and Solutions of Asynchronous Programming
VII. Conclusion

I. Preface

Introduction

Asynchronous programming is a programming method in computer programming, which is different from traditional synchronous programming. It allows the program to continue to perform other operations while waiting for a certain operation to complete , so as to achieve asynchronous execution.

In traditional synchronous programming, the program will be executed in the order of the code, but when performing some operations, such as network request, file reading or database query, etc., these operations need to wait for the response or read At this time, the program will be blocked and can only be in a waiting state until the operation is completed before continuing to execute the following statement.

In this case, if the operation takes a long time, it will cause the program to respond slowly, or even crash. Asynchronous programming can solve these problems through technologies such as callback function, Promise object, async and await, so that the program can perform other operations while waiting for some operations to complete, which is more efficient, flexible and scalable .

Application of asynchrony in computer programming

Asynchronous programming is widely used in computer programming, the following are some common examples:

Network request: When making a network request, if the synchronous method is used, the program will be blocked. But using the asynchronous method, you can continue to execute the following code after sending the request, without wasting time waiting for the server to respond.
File reading and writing: File IO will block the program if it uses synchronous mode, but using asynchronous mode can make the program perform other operations while waiting for the completion of file reading and writing.
Database query: The database query may be performed on the network and requires a certain amount of processing time. If you use the synchronous method, you must wait for the response returned by the query. But use the asynchronous way to perform other tasks while waiting for the response.
GUI application: Through asynchronous programming, it can prevent the interface from being stuck due to the long processing time of a single event, thereby improving the response speed and user experience of the application.
Game development: Game development requires a lot of calculations and input and output operations. Using asynchronous methods can avoid problems such as freezes and delays, thus making the game smoother.

In short, asynchronous programming has important application value in computer programming. It can avoid program blocking, improve program efficiency and response speed while performing calculation tasks, thereby improving the user experience of the application program.

II. Synchronous and asynchronous

Definition and difference

Synchronous and asynchronous are two different modes or ways of execution in computer programming.

Synchronous (Synchronous) refers to when performing an operation, you need to wait for the completion of the previous operation before starting the subsequent operation. Synchronous code execution is controlled by the program, and only one task is executed at a time, and each task must be executed after the previous task is completed. In synchronous mode, when an operation takes a lot of time, the execution of the program will stall and wait for the operation to complete. This method is usually used to solve some simple tasks, such as data processing and graphical user interface operations, but it will cause the program to block, and for operations with large time overhead, it will seriously affect the performance of the entire program.

Asynchronous (Asynchronous) refers to you can perform subsequent operations without waiting for the completion of the previous operation. Asynchronous code execution is not controlled by the program, because it is usually driven by events, and the execution of each task will not block the previous operations, that is to say, it will not hinder the execution of other codes while waiting for data. The program only needs to register a callback function when calling an asynchronous operation, and the callback function will be executed automatically when the operation is completed. This method is usually used to solve some tasks with background processing, such as network requests, file reading and GUI applications, etc., which can improve the efficiency and response speed of the program.

Summary: The main difference between synchronous and asynchronous is whether the program can perform other operations while waiting for the operation to complete. Synchronous operations will block the program, resulting in a fixed program execution order, while asynchronous operations will not block the program, and other operations can be performed at the same time, improving the efficiency and response speed of the program.

Disadvantages of synchronous programming

The main disadvantage of synchronous programming is that the program will be blocked while waiting for some operation to complete until the operation is completed, which will cause the program to appear inefficient or even freeze.

Specifically, the disadvantages of synchronous programming include:

Blocking the main thread: In synchronous programming, when an operation takes a lot of time, the entire program will be blocked, waiting for the operation to complete, which will cause the main thread to be unable to be released and other operations to be performed. Task.
Complicated code structure: In synchronous programming, in order to ensure that the code can be executed correctly in order, multiple operations need to be nested and called, which will make the code structure complex and difficult to read and maintain.
Slow program performance: In synchronous programming, the performance of your program suffers because it waits for operations to complete before continuing. If you wait too long, the program may freeze and crash.
Not easy to expand: In synchronous programming, adding new tasks will cause the execution sequence of the program to change, which will affect the correctness of the entire program. At the same time, synchronous programming often needs to write a whole piece of code completely, so that it is not easy to segment the code.

To sum up, although synchronous programming is easy to understand and implement, its shortcomings also make it difficult to adapt to large-scale, high-concurrency modern application scenarios, so asynchronous programming came into being.

III. Asynchronous programming

Definition

In the field of computer programming, asynchronous programming means that when executing code, it does not need to wait for the result of an operation, but responds to it after the operation is completed, so as to realize asynchronous operation and multi-task concurrent execution. Different from synchronous programming, asynchronous programming can not block the main thread when performing time-consuming operations, but triggers relevant responses as soon as possible when the operation is completed through technologies such as callback functions, Promise objects, async, and await.

Asynchronous programming is widely used in scenarios involving network IO, disk IO, and massive computation, such as web applications, game development, data mining, machine learning, etc. Through asynchronous programming, the program can perform other tasks while waiting for certain operations to complete, thereby improving the performance and efficiency of the program, and making the code more flexible, scalable, and maintainable.

In short, asynchronous programming is an efficient, flexible, and scalable programming method, which can bring great benefits when dealing with a large number of complex I/O operations and computationally intensive tasks.

Application scenario

Asynchronous programming has many broad application scenarios in modern computer programming. Here are some common application scenarios:

Network programming: In client and server-side network programming, multi-user concurrent requests and processing can be realized through asynchronous programming. When processing network requests and responses, the main thread does not need to be blocked, which improves the response of the program speed and efficiency.
File processing: For the read and write operations of large files, asynchronous programming allows the program to perform other operations while waiting for the IO operation to complete, avoiding program blocking and improving program efficiency.
GUI application: Asynchronous programming can prevent GUI applications from being stuck and unresponsive when performing computationally intensive or network request operations, thereby improving the user experience of the application.
Database query: Database query may involve the associated query of multiple tables and the processing of a large amount of data. Using asynchronous programming, you can perform other tasks while waiting for the query results, avoiding program blocking and unresponsive situations.
Game development: In game development, a large amount of game data, game logic calculation and network data communication operations can be processed through asynchronous programming, improving the efficiency and response speed of the game.
Data mining and machine learning: Data mining and machine learning need to deal with a large amount of data and computing tasks. Asynchronous programming can help programs not get stuck in a blocked state while waiting for IO operations when processing these tasks, thereby improving Computational efficiency.

Overall, asynchronous programming has a very wide application and an important role in many fields of computer programming, which can improve the efficiency, response speed and user experience of programs.

Callback function

In asynchronous programming, callback function is a common implementation.

The callback function points to a function called by the asynchronous operation. When the asynchronous operation is completed, the function will be called to notify the relevant code of the processing result.

Callback functions are often used to process responses to asynchronous requests, such as network communication, file reading, and database query. For example, when performing an asynchronous network request, it is usually necessary to register a callback function to process the request result. When the request is completed, the callback function will be called to process the response result of the request.

The callback function is usually passed as a function parameter, which can be an anonymous function or a named function, and can also contain any number of parameters. Once the asynchronous operation completes, the callback function is called, returning information about the result of the asynchronous operation.

Although the callback function is a common pattern in asynchronous programming, it has some disadvantages. Too many nested levels of callback functions are prone to callback hell, the code is poorly readable, and it is difficult to debug and maintain. Therefore, modern asynchronous programming techniques usually use Promise and async/await instead of callback functions to improve code readability and maintainability.

Promise object

Promise is a technology that decouples callback functions from asynchronous operations. It can connect asynchronous operations, reduce the number of nested layers of callback functions, and improve the readability and maintainability of asynchronous code.

In JavaScript, Promise objects represent the final state of an asynchronous operation (i.e. completed or failed), and callback functions can be bound to these states. It has three states: pending (in progress), resolved (completed), and rejected (failed). When the asynchronous task is completed, the Promise object will be marked as completed by calling the resolve function, and the result of the asynchronous operation processing will be returned; if the asynchronous task fails, the Promise will be marked as rejected by calling the reject function, and an error message will be returned.

The Promise object has two important methods, then() and catch(). Among them, the then() method calls the callback function when the Promise object is successfully completed, and the catch() method calls the callback function when the Promise object fails. Use the then() and catch() methods to gracefully handle the success and failure of asynchronous operations without excessive nesting of callback functions.

The sample code is as follows:

function asyncFunction() {<!-- -->
  return new Promise(function(resolve, reject) {<!-- -->
    // asynchronous task code
    if (/* async task completed successfully */) {<!-- -->
      resolve(result); // success condition
    } else {<!-- -->
      reject(error); // failure condition
    }
  });
}

asyncFunction()
  .then(function(result) {<!-- -->
    console.log(result); // the result of a successful asynchronous operation
  })
  .catch(function(error) {<!-- -->
    console.log(error); // The reason why the asynchronous operation failed
  });

In short, Promise is an elegant and maintainable asynchronous programming technique that can greatly improve the way asynchronous callback functions are used.

async/await keyword

async/await is an asynchronous programming technology introduced in ES2017. It is a more concise, more readable, and easier to maintain programming method, which can make asynchronous code look like synchronous code.

The async keyword is used to define an asynchronous function, and the await keyword is used to suspend the execution of the asynchronous function and wait for the Promise object to return the result, thereby avoiding the nesting of callback functions. When the await keyword is used to wait for the Promise object, the execution of the asynchronous function will be suspended until the Promise object returns the result before continuing to execute the following code. During the suspension of execution, the JavaScript engine will continue to execute other codes, making the program more efficient.

The sample code is as follows:

async function fetchData() {<!-- -->
  try {<!-- -->
    const response = await fetch('/api/data');
    const data = await response. json();
    return data;
  } catch (error) {<!-- -->
    console. log(error);
  }
}

fetchData()
  .then(data => {<!-- -->
    console. log(data);
  })
  .catch(error => {<!-- -->
    console. log(error);
  });

In the above sample code, the fetchData() function is defined with the async keyword and waits for the result of the asynchronous operation through the await keyword. When the data is successfully obtained, the status of the returned Promise object becomes completed, thus triggering the then() callback function; if an error occurs, the status of the returned Promise object becomes rejected, thereby triggering the catch() callback function.

In short, the async/await technique simplifies the operation of asynchronous programming and improves readability and maintainability by making asynchronous code execute more like synchronous code, which makes it an important part of modern programming practice. One of the techniques.

Event loop

The event loop is a programming model common in front-end programming and asynchronous IO. The core idea of the event loop is: during the execution of the program, let a piece of code be in a waiting state (asynchronous), wait for an event to occur, then add the event to the event queue, wait for the event loop to detect this event and execute the corresponding Callback.

Event loops are very common in programming, such as the Event Loop of browsers, the Event Loop of Node.js, and so on.

In front-end development, the event loop can be used to handle asynchronous requests and user interaction events on the page, such as click events, keyboard events, etc. In back-end programming, the event loop can be used to handle asynchronous operations such as network IO.

In general, the event loop can improve the concurrency performance of the program, reduce the blocking and waiting time of the program, and improve the operating efficiency of the program.

IV. Asynchronous programming example

Asynchronous programming in Node.js

In Node.js, most of the core modules are in the form of asynchronous IO, such as file reading and writing, network requests and so on. This is because Node.js is based on event-driven, and its event loop mechanism allows the program to process other things while waiting for a certain IO to complete, which improves the efficiency and performance of the program.

In order to take advantage of the asynchronous nature of Node.js, developers can use the following common asynchronous programming methods:

Callback function: The most basic and common asynchronous programming method in Node.js is the callback function. Pass the callback function into the asynchronous function, and call this callback function when the asynchronous operation completes.
Promise: Promise is a kind of encapsulation of callback function. Promise is used to handle the results of asynchronous operations, which can make the code look clearer and more concise.
async/await: async/await is a syntax introduced by ES2017, which can make asynchronous programming easier and easier to read. async/await makes asynchronous operations look like synchronous operations, and the code is more readable.

In general, there are many options for asynchronous programming in Node.js. Developers can choose a suitable method according to their needs to improve the efficiency and maintainability of the program.

Asynchronous HTTP request implementation

In Node.js, you can use the built-in http/https module to implement asynchronous HTTP requests. Here is a simple example:

const https = require('https');

const options = {<!-- -->
  hostname: 'www.example.com',
  port: 443,
  path: '/api/something',
  method: 'GET'
};

const req = https.request(options, (res) => {<!-- -->
  console.log(`statusCode: ${<!-- -->res.statusCode}`);

  res.on('data', (d) => {<!-- -->
    process.stdout.write(d);
  });
});

req.on('error', (error) => {<!-- -->
  console. error(error);
});

req. end();

In this example, the https.request function can initiate an HTTP/HTTPS request and return a ClientRequest object. The result of the request can be obtained through event monitoring, such as calling the res.on(‘data’, …) function to monitor the return of data.

When an error occurs with the request, the error can be handled by listening to the error event on the req object.

It should be noted that if you are sending large-scale requests in Node.js, you can consider using third-party modules in Node.js such as axios and request. They support multiple requests at the same time and control the number of concurrent requests. Take advantage of the concurrency of asynchronous requests.

Asynchronous file operations

In Node.js, you can use the fs module for asynchronous operations on files. Here’s an example of a basic asynchronous file read:

const fs = require('fs');

fs.readFile('/path/to/file', (err, data) => {<!-- -->
  if (err) {<!-- -->
    console. error(err);
    return;
  }

  console.log(data.toString());
});

In this code fragment, the file is read through the readFile function, and the data is returned after the file is read, and then the operation is performed in the callback function.

If you need to write to a file asynchronously, you can use the writeFile function:

const fs = require('fs');

const content = 'hello world';

fs.writeFile('/path/to/file', content, (err) => {<!-- -->
  if (err) {<!-- -->
    console. error(err);
    return;
  }
  
  console.log('write file success');
});

In addition to the readFile and writeFile functions, the fs module also provides many other asynchronous operations, such as asynchronously creating directories (mkdir), asynchronously reading directories (readdir), and so on.

V. Advantages of asynchronous programming

The main advantages of asynchronous programming are as follows:

Improve program performance: The biggest advantage of asynchronous programming is that it can improve program performance. In traditional synchronous programming, if some operations need to wait for the result before continuing to execute, other operations will have to wait forever and cannot be executed concurrently. In asynchronous programming, the program can continue to perform other tasks while waiting for an asynchronous operation to complete, which greatly improves the operating efficiency and throughput of the program.
Reduce resource waste: Asynchronous programming can handle multiple asynchronous operations at the same time, reducing resource waste. Because the synchronous operation will make the program wait forever, wasting CPU time and system resources. While waiting for the result, the asynchronous operation can allow the program to continue to perform other operations, reducing the waste of resources.
Improve code readability: Asynchronous programming usually uses methods such as callback, Promise, async/await, etc., which can make the code look more concise and easy to read. Especially when dealing with complex logic and multiple asynchronous operations, compared with synchronous programming, asynchronous programming can better organize the code and control the flow of the program, and improve the readability and maintainability of the code.

In general, asynchronous programming is an indispensable and important feature in modern programming, which can make programs more efficient, resource utilization higher, and code more concise and understandable.

Others: improve user experience / avoid blocking the main thread

VI. Challenges and Solutions of Asynchronous Programming

Asynchronous programming also brings some challenges, such as:

Callback Hell: If callbacks are used for asynchronous programming, the problem of callback hell may arise. That is, nesting too many callback functions will greatly reduce the readability and maintainability of the code, making the code confusing and difficult to maintain.

Solution: Using Promise or async/await can effectively solve the problem of callback hell, improve the readability and maintainability of asynchronous programming code to a new level, and it is more in line with modern programming standards.

Exception handling: In asynchronous programming, since asynchronous operations are executed asynchronously, it is difficult to catch exceptions of asynchronous operations. If there is no proper exception handling method, abnormal errors are easy to occur, resulting in program crash or data loss.

Solution: For asynchronous programming in the form of callbacks, you can use the try-catch method in the callback function to catch exceptions. For Promises and async/await, you can use the catch method to catch exceptions. At the same time, log output and alarms can be used to detect and solve abnormal problems in time.

Concurrency control: Asynchronous programming often involves concurrency control. If there are too many concurrent operations, system resources will be strained, and program operation efficiency will decrease, thereby affecting program performance.

Solution: You can use some tools to control the amount of concurrency, such as async.js, bluebird, axios, etc. These tools have the ability to handle asynchronous request concurrency control.

Difficult to debug: In asynchronous programming, when a problem occurs, it is difficult to locate the location and cause of the problem, which makes debugging difficult.

Solution: You can use Node.js debugging tools, such as Node.js inspector, and use log output to capture and output detailed information about program errors in a timely manner, thereby improving the efficiency of troubleshooting. At the same time, you can also use some debugging tools for asynchronous programming, such as Node-Async-Debugger, etc.

VII. Conclusion

The future of asynchronous programming is bright. With the continuous growth and complexity of modern applications, asynchronous programming has become a necessary programming style. Asynchronous programming will be more common in the future because it can significantly improve application performance, reduce resource waste, and improve code readability and maintainability.

Therefore, future asynchronous programming will face the following challenges:

More popular asynchronous programming methods: With the development and development of technology, asynchronous programming will adopt more and more popular programming methods, such as Reactive Programming and Event Sourcing, to improve the scalability and performance.
Better error handling and debugging: Developers will increasingly demand better error handling, including better error stacks, application performance monitoring, and better debugging mechanisms.
Better concurrency handling: As the performance of applications continues to improve, developers need better concurrency control mechanisms to ensure that applications can effectively handle concurrent requests and high loads.

In general, asynchronous programming is an important part of application performance and maintainability, and it will continue to evolve and grow to ensure that applications are more stable and efficient in the future.