25. Asynchronous programming

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Asynchronous programming is a programming paradigm that focuses on executing tasks independently of the main flow of program execution. This type of programming is extremely useful when dealing with operations that can take considerable time to complete, such as network requests, reading files from disk, interacting with databases, and other I/O operations.

In traditional synchronous programming, the program runs from top to bottom, line by line. Each line of code must complete before the next one is executed. This can lead to performance issues, especially when a time-consuming task is running. While this task is being processed, the entire program is effectively blocked, which can result in a poor user experience, especially in web applications.

Asynchronous programming solves this problem by allowing time-consuming tasks to run in parallel with the rest of the program. This is done by starting the time-consuming task and then continuing with the rest of the program, without waiting for the time-consuming task to finish. When the time-consuming task completes, it can return the result to the main program or execute some callback code.

There are several techniques for implementing asynchronous programming, including callbacks, promises, and async/await.

Callbacks are functions that are passed as arguments to other functions. When the main function finishes executing a task, it calls the callback function with the result. This allows the program to continue executing other tasks while it waits for the long-running task to complete.

Promises are objects that represent the eventual result of an asynchronous operation. A promise is in one of three states: pending, fulfilled, or rejected. When the asynchronous operation completes, the promise is fulfilled with the result value, or rejected with a failure reason. Promises can be chained, allowing asynchronous operations to be executed in sequence.

Async/await is a special syntax introduced in many modern programming languages ​​that makes asynchronous code easier to write and understand. A function marked async always returns a promise. The await keyword can be used inside an async function to pause code execution until a promise resolves or rejects.

Although asynchronous programming can be more complex than synchronous programming, it offers many benefits. It can significantly improve a program's performance and responsiveness, especially in web applications. However, it is also important to understand the pitfalls and challenges of asynchronous programming, such as error handling and task synchronization.

In summary, asynchronous programming is a powerful tool in a programmer's toolbox. With a good understanding of how it works and when to use it, you can write more efficient and responsive code that provides a better user experience.

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2626. Concurrent and parallel programming