Python server programming skills: implementing asynchronous I/O programming

As an interpreted programming language, Python has very powerful library support, including various libraries related to network programming. In the field of server programming in Python, asynchronous I/O programming is a very important technology. This article will introduce what asynchronous I/O programming is, why using asynchronous I/O is more efficient, and introduce the techniques for implementing asynchronous I/O programming in Python.

What is asynchronous I/O programming?

In traditional synchronous I/O programming, the program usually blocks to wait for one operation to complete before proceeding to the next operation. Due to the slow network transmission speed, such waiting will cause the program execution efficiency to be extremely low and the computer resources cannot be fully utilized.

Asynchronous I/O programming is a programming method that no longer blocks and waits. It can continue to execute subsequent code while waiting for the I/O operation to complete. This is achieved using an asynchronous event loop mechanism and non-blocking I/O operations.

Through asynchronous I/O programming, multiple I/O operations (such as reading and writing files, network requests, etc.) can be executed simultaneously and wait for all I/O operations to be completed before proceeding to the next step. This enables efficient concurrent processing.

Why use asynchronous I/O programming?

Compared with synchronous I/O programming, asynchronous I/O programming has some very obvious advantages:

1. Higher efficiency: Asynchronous I/O programming can make full use of the computer resources to improve program execution efficiency. This is because when an I/O operation is waiting, you can immediately switch to another operation instead of waiting to be blocked, thus avoiding the waste of waiting time.
2. Better scalability: In asynchronous I/O programming, applications can handle multiple connections simultaneously without blocking or exhausting thread resources. This makes asynchronous I/O programming easier to support large numbers of concurrent connections.
3. Better responsiveness: Asynchronous I/O programming can make the program more flexible, respond to user requests in a timely manner, and complete I/O operations faster when handling a large number of concurrent connections.

Tips for implementing asynchronous I/O programming

In Python, implementing asynchronous I/O programming requires the use of relevant libraries. The following libraries are commonly used asynchronous I/O libraries in Python:

1. asyncio: The asynchronous I/O library in the Python standard library provides operating system-level asynchronous I/O support and can handle Asynchronous network connections and IPC (inter-process communication).
2. Tornado: A very powerful Web framework and an asynchronous I/O library with high-performance asynchronous network library and asynchronous I/O functions.
3. gevent, etc.: In addition to the asynchronous I/O library in the Python standard library, there are some third-party libraries that also provide very good asynchronous I/O support.

Next, we will take the asyncio library as an example to introduce the techniques of asynchronous I/O programming in Python.

1. Coroutine definition

In the asyncio library, coroutine is the basic unit of asynchronous programming. It is a lightweight thread that can be used in a thread. Execute multiple coroutines concurrently. A coroutine can be viewed as a function that can pause and resume execution. It can use the yield statement to pause its execution. In Python 3.5 and above, the async/await keyword makes it easier to create and manage coroutines.

The following is a simple coroutine example:

import asyncio

async def coroutine_demo():
    print("Start")
    await asyncio.sleep(1)
    print("End")

The above code defines a coroutine named coroutine_demo, and the await statement is used in the coroutine to indicate that the coroutine is running Execution will be paused while waiting for the asynchronous I/O operation to complete. The sleep function in the asyncio library is used here to simulate the waiting time during I/O operations.

2. Event loop

The event loop in the asyncio library is the core of asynchronous I/O operations. The event loop uses an infinite loop to listen for asynchronous events. When an event occurs, it can be processed and returned immediately. The event loop can be understood as a message system, where messages are the results of asynchronous I/O operations.

The following is an example of a simple event loop:

import asyncio

async def coroutine_demo():
    print("Start")
    await asyncio.sleep(1)
    print("End")

loop = asyncio.get_event_loop()
loop.run_until_complete(coroutine_demo())
loop.close()

In this example, a coroutine named coroutine_demo is first defined. Then, an event loop is created and the coroutine_demo coroutine is run using the run_until_complete() method. After running, the coroutine will output "Start" on the first line, and then wait for 1 second before outputting "End".

It should be noted that the event loop must run in the main thread. If we call the run_loop() method in other threads, the program will throw an exception.

3. Callback function

In asynchronous I/O programming, when an asynchronous event occurs, the event loop will notify the coroutine to execute the corresponding callback function (callback function). The callback function is an ordinary function used to handle the results of asynchronous I/O operations.

The following is a simple callback function example:

import asyncio

async def coroutine_demo():
    print("Start")
    await asyncio.sleep(1)
    print("End")

def callback_func(future):
    print("Callback function")

loop = asyncio.get_event_loop()
future = asyncio.ensure_future(coroutine_demo())
future.add_done_callback(callback_func)
loop.run_until_complete(future)
loop.close()

In this example, the function callback_func is a callback function that is called when the coroutine finishes running.

4. Asynchronous I/O operations

In asynchronous I/O programming, almost all I/O operations need to be encapsulated into coroutines using the async/await keyword . For example, you can use the open function in the asyncio library to read and write files asynchronously:

import asyncio

async def read_file(path):
    async with aiohttp.ClientSession() as session:
    async with session.get(path) as response:
        return await response.text()

loop = asyncio.get_event_loop()
result = loop.run_until_complete(read_file("http://example.com"))
loop.close()

In this example, we use the ClientSession object of the aiohttp library to make an asynchronous HTTP request, and after getting the response, use the await keyword to get the response. text() is the key to making asynchronous I/O wait.

Summarize

Как упоминалось выше, асинхронное программирование ввода-вывода — это эффективная модель программирования, которая может значительно повысить эффективность выполнения и скорость реагирования программы. Язык Python имеет очень богатую библиотеку асинхронного ввода-вывода, включая библиотеку asyncio стандартной библиотеки Python и сторонние библиотеки Tornado и gevent. Изучение навыков программирования асинхронного ввода-вывода очень важно для серверных программистов Python.

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